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A2 Biology Revision
Transcript of A2 Biology Revision
are essential for monitoring changes in conditions within an organism or environment. they detect the changes in the conditions but will only respond if and when the condition/conditions change, such a change is known as a
. one example of this is when the pressure of an insect , such as a fly, on the surface of a Venus flytrap, causes the receptor cells on the surface of the plant to trigger a
(a change in the
as a result in a change in environment), in this case the snapping shut of the "trap" in order capture the insect
the need for communication between cells
multi-cellular organisms have many differentiated cells specialized for particular functions, allowing them to perform tasks more efficiently. groups of cells form tissues and organs. as one cell would be unable to perform all the tasks for survival a
is required to allow them to work together
one example of such a process is the excretion of waste products from metabolic activity, firstly from the tissue fluid into the blood and then from the body altogether , the stimulus is the waste products that are noticed by receptor cells (which are responsible for detecting changes in the internal and external environment) so they dont reach toxic levels , one response may be a temporary drop in metabolic activity to help reduce the buildup of these products
introduction to communication
cell signaling is the process in which a cell interacts with the environment around it , this involves a cell releasing a molecule that's detected by another cell provoking a response.
the molecules are collected to trigger a response by the target cell (the cell the molecule is being sent to) using a receptor (such as a glycolipid/ glycoprotine) embedded in the cell membrane that is complimentary to the shape of the molecule involved, so that other hormones/ molecules used by the body cant activate it.
cell signaling pathways are the distances/routes that the the chemicals are released to travel , they can be split into three categories:
Endocrine signaling where chemicals are release in order to travel long distances usually through the circulatory system
Paracrine signaling which occurs between cells that are close together , ether directly or by and extracellular fluid
Autocrine Signalling is where the cell releases molecules in order to trigger a response from itself
some medicinal drugs work by ether activating/ blocking a cells receptor sites by imitating the shape of the molecule used to activate it to ether inhibit or trigger a specific bodily process.
is the maintenance of a consistent
, the factors that are monitored and maintained include
temperature, water potential of the blood, blood glucose concentration, pH, blood pressure , ion concentrations within the blood. receptor cells are used to monitor these conditions. one specific example is tissue fluid composition is controlled by regulating the composition of the blood.
positive and negative feedback
occurs in many
(organisms that take small inorganic molecules and convert them into larger organic molecules), these organisms are known as
this reaction takes place in the
(specialist organelles found inside the plant cells), it has too stages the
light dependent stage
light independant stage
receptor detects the change
change away from optimum
communication system informs effector
effector reacts to reverse the change
return to optimum conditions
change away from optimum
receptor detects the change
informs the effector
effector reacts to
used to maintain a fairly constant internal environment by activation of a control system when a change occurs to return conditions to there optimum level
a process in which a condition changes and is detected by the receptors, however the actions taken by the body brings about a further increase in that change, though usually harmful there are a number of occasions in which its helpful.
another example is excretion which is the removal of waste products of the
Ectotherms are organisms that rely on their surroundings to gain body heat, so therefore there body temperature is always dependent on the surrounding environmental temperature. however many ectotherms are able to regulate there body temperature through behavioral adaptations (e.g. lizards sun basking or hiding in the shade to raise or lower there temperature).
Endotherms are organisms that use internal mechanisms in order to regulate there body temperature , this is known as thermoregulation , receptors detect changes in the temperature of the environment (peripheral temperature receptors in the skin), and in the internal core temperature (core temperature receptors in the hypothalamus of the brain). The control system (also in the hypothalamus of the brain) then sends out instructions to effectors to reverse the changes.
may have been formed by
that created a symbiotic relationship with primeval eukaryotic cells , evidence for this includes the spiral DNA found in chloroplasts and similar ribosomes, the structure of a chloroplast is seen below
methods used my endotherms to conserve body heat
capilleries widen so more blood flows flows close to the skin surface to lose heat radiation by convection , this helps to cool you down
blood is diverted to flow further from the surface by narrowing capillaries so radiation and convection are reduced, this helps to conserve heat
produce sweat that evaporates from the skin cooling the organism
homeostasis for body heat regulation
rise in core temp
drop in core temp
thermoregulatory system in
hypothalamus detects change
nervous system and
hormonal system carry
signals to the skin, liver and
less heat generated
and more heat lost
this ensures that a steady optimum state can be maintained .
for it to occur
a change must be detected
a change must be signaled to other cells
there must be a response to reverse the change
nervous system and
hormonal system carry
signals to the skin, liver and
thermoregulatory system in
hypothalamus detects change
less heat generated
and more heat lost
optimum body temperature (37 degrees C)
photosynthsis, a breif A2 summary
light dependent stage (thylakoid membranes)
light indipendant stage (stroma)
the light dependent stage
in the light dependent stage....
synthesis of ATP (photophosphorylation)
two types of photophosphorylation ,non- cyclic which involves both photosystems and cyclic which uses only one photosystem
splitting of water (photolysis) to produce H+ hydrogen ions and electrons e-
picking up of H+ by NADP to form NADPH (also known as reduced NADP)
This occurs in the tylakoid membrain
Both photosystems are part of this stage (see later slide) :
Photosystem one occur mainly on intergranal Lamellae
Photosystem two Occur almost exclusivly on granal lamellae
Pigments in Photosystems trap light energy to convert it into Chemical Energy (ATP)
Light independent stage
in the light independent stage
fixation of carbon dioxide occurs
and conversion to carbohydrates using ATP and Reduced NATP
ADP + pi
ADP + Pi
Light Dependent stage : the role of water
Water is the source of:
Hydrogen ions used to make ATP then accepted by NADP
Electrons to replace those lost by chlorophyll
water also provides the by product of photosynthesis (oxygen)
it is also used to keep the plant cells turgid and therefore able to function efficiently
Photolysis of water occurs on PSII (contains the relevant enzyme)
4H+ + 4e- + O2
types of receptors
light sensitive cells in the retina of the eye that detect light intensity changes and the changes in the range of wavelengths
Olfactory cells lining the inner surface of the nasal cavity detect the changes in the presence of volatile chemicals
taste buds in the tongue, hard palate, epiglottis and the first part of the oesophagus detect changes in the presence of soluble chemicals
pressure receptors in the skin detect pressure on the skin
sound receptors in the inner ear detect vibrations in the air
muscle spindles detect changes in the length of muscle fibers
Generating nerve impulses
neurones are specialized channel proteins that are specific to the moving of potassium and sodium ions. They also posses a gate that can open or close the channel, when the gate is open, permeability to that particular ions is increased , when closed its decreased, though usually there closed.
nerve cell membranes also have carrier proteins , but these transport sodium ions out of the cell and potassium ions into the cell. these are known as sodium potassium ion pumps. as more sodium ions are transported out of the cell than potassium into the cell, the cell becomes negatively charged as a result and is known as a
nerve impulses are produced by increasing the permeability of sodium ions to the cell, this happens by causing the sodium channels to open allowing sodium ions to go down there concentration gradient into the cell, this causes the charge of the cell to become less negative than usual
Table to compare Sensory and Motor Neurones
sensory receptors -
specialized cells that detect changes in the environment , they are energy transducers that convert one form of energy into another
carry's action potential from the sensory receptor to the CNS
carry's an action potential from the CNS to an effector
connects sensory and motor neurones
transmits action potential from one part of the body to another
the z scheme (flow of electrons in the light dependent reaction), non-cyclic photophosphorilation
light (a photon) hits photosystem 2 (containing P680), the energy is transferred to 2E-'s and they become exited (raised to a higher level) , this also causes the photolysis of water molecules in the photosystem
these electrons are emitted and captured by electron acceptors and passed along a series of electron carriers (proteins that carry iron atoms ) embedded in the thylakoid membrane.
the energy released is used to make ATP from ADP + Pi
light is absorbed by photosystem 1 (containing P700) and passed to two e- 's that become exited and are then emitted from the photosystem
P680's electrons replace P700's
P680 is reduced by the electrons from Photolysis
(for those that do Chemistry its similar to O.I.L.R.I.G)
the hydrogen ions combine with the electrons held by the second electron acceptor to give NADPH
no photolysis of water
no generation of reduced NADP
Small amounts of ATP made
Guard cells only contain PhotoSystem 1's
photosynthetic pigments are large organic molecules that absorb some wavelengths of light , for use in photosynthesis , and reflect others.
different photosynthetic pigments absorb different wavelengths of light and each also has a specific peak absorption rate which is the wavelength that they can absorb the easiest and the quickest.
(composed of inner and
when a neurone is at resting potential it maintains a potential difference in charge across the cell membrane (the membrane is polarized ) , the inside of the cell is maintained at -60 to -70v compared to the outside of the cell (this is known as threshold potential ), the neuronal membranes contain potassium ion pumps that maintain the potential difference by pumping three sodium ions out of the cell for every two potassium ions taken in , it uses ATP to power the process. this also means that the neurone is not transmitting and is said to be at rest.
the membrane is also permeable to potassium ions so some potassium ions are lost from the cell via diffusion , the sodium ion channels remain closed to prevent the sodium ions access into the cell.
transmittion of nerve impulses
neurones transmit impulses as a series of
when a neurone is stimulated by ether technology, chemical the axon becomes
(loses its normal polarization) . the voltage gated sodium ion channels then open ,due to the change in potential difference across the cell, to allow sodium ions into the cell , as a result of this the inside of the cell becomes less negative compared to the outside. if enough sodium ions flow into the cell it will reach threshold potential which will open more sodium ion channels (this is an example of positive feedback) , more sodium ions flow into the neurone , causing the interior cell have +40mv compared to the outside , this is known as
. after the sodium ions enter the cell the channels allow potassium ions out of the cell this reduces the
across the cell again returning it to - 60mv
, this is known as
(the membrane also falls temporarily below normal resting potential, this is called
the light independent stage
ATP: adonosine triphosphate
GP: Glycerate 3-phosphate
NADP: nicotinamide adenine dinucleotide phosphate
PSI & PSII: photosystems 1 or 2
Rubisco : ribulose biphosphate carboxylase
RuBP : 1,5 biphosphate
occurs in three stages, collectively called the Calvin cycle
ribulose 1,5 bisphosphate (RuBP) regeneration
Occurs in the dark but stops soon after light becomes unavalible as it draws on energy from the light dependant stage
the Calvin cycle (for an explanation ,if your confused, see the next slide:) ).
the Calvin cycle : an understandable (hopefully) explanation
Carbon dioxide is absorbed from the atmosphere and is fixed (combined) with
RuBP , the rubisco enzyme speeds up the process to form an unstable 6 carbon compound , which is then rapidly broken down into two molecules of GP. the carbon dioxide has now been fixed
This GP is then converted into TP (triose phosphate) , by reducing reduced NADP and ATP this TP can be used by the plant to manufacture a variety of large organic molecules (e.g. amino acids and some carbohydrates).
however the majority of the TP ( 5 in every 6 produced) is recycled to produce more RuBP, this is done using ATP from the light dependent stage to provide energy and a phosphate group.
Direction of transmission
node of Ranvier
transmission of action potential
neurone components and there functions in action potential transmission
myelin sheath (for more details on this part of the neurone see later on in the prezi)
an insulating layer of fatty materials that stop the diffusion of potassium ions to ensure that the ionic materials that create action potential cannot occur over much of the length of the neurone in order to speed up transmission .
nodes of ranvier
gaps in the myelin sheth that allow the ionic movements that generate action potential. sodium ions diffuse from one node of ranvier to the next, causing action potential to appear to "jump" from one node to the next .
the cells that make up the Myelin sheath
the opening of the sodium ion channel at one particular point of the neurone upsets the balance of the sodium and potassium ions , this creates local currents in the cytoplasm of the neurone , this causes sodium channels further along the membrane
when an action potential occurs the sodium ion channels open at particular points along the neurone
this allows sodium ions to diffuse across the membrane from regions of higher concentration outside the neurone into the neurone
the movement of sodium ions into the neurone upsets the ionic concentrations inside the cell
the concentration of sodium ions then increases to the point where the sodium ion channels open
this causes the sodium ions to diffuse sideways away from the region of increased concentration , this movement of ions is known as a local current
limiting factors of photosynthisis
photosynthesis is a complicated process that is involves a number of factors , any one of them can become a limiting factor if there is a limited supply of this factor , only one factor (the one in the least supply) can limit the process at one time.
CO2 constitutes of 0.03-0.06% of the earths atmosphere , 500 million years ago there was 20x this amount in the atmosphere, this fell in the carboniferous period with the evolution of large plants, rose again during the jurassic and triassic and then decreased untill the start of the industrial ages.
if CO2 concentrations rises the rate of photosynthesis increases untill another limiting factor prevents any further increase as more CO2 can be fixed into GP, then TP and so on (on a graph this will result in a plateau in the graph), though this is limited by water loss from the stomata to let the CO2 in , as if the plant cannot get enough water via the roots to replace that lost via transpiration it may result in wilting , so the plant may have to close its stomata to prevent this in warm temperatures, cutting off/ Reducing the CO2 supply and reducing the rate of photosynthesis . if the CO2 concentration falls , this effects fixation so less GP is produced, so less TP can be synthesis. this means more RuBP will be produced.
if light intensity increases , again the photosynthesis rate will increase untill another factor limits the process, it will also cause the plant to open its stomata to let in more CO2 to the leaves, causing the light dependent stage to accelerate, producing more ATP and NADPH accelerating the light independent stage, meaning greater production of lipids and amino acids E.C.T. a reduction in light will slow the light dependent stage, this will cause a reduction in the production of ATP and Reduced NADP in the light dependent stage, slowing the light independent stage as less GP is converted to TP and less TP can be used to regenerate RuBP , so the GP concentration remains high whilst concentrations of RuBP and TP drops . reducing the quantity of CO2 fixed.
temperature also has an effect on the rate of photosynthesis , though it dosent effect the light dependant stage , the light independent stage utilizes enzymes that can be slowed by a drop in temprature or denatured by a too great a rise in temperature. between 0 and 25 degrees C the rate of photosynthesis doubles for every 10 degree rise in temperature. above 25 degree the rate levels off and then starts to drop as the heat alters the active site of the RuBisco enzyme preventing it from accepting carbon dioxide . in fact it can alter the active sites so the enzyme is more likely to accept oxygen molecule instead of CO2 molecules , resulting in increased photorespiration. there is also an increased water loss from the leaves v=with increased temperature via transpiration, which can result in the plan wilting.
how chloroplasts are adapted to perform there functions
is a junction between two or more neurones. it where one neurone can communicate with or signal too another neurone , between the two neurones is a small gap (approximately 20NM wide) called the synaptic cleft. action potential is produced by the movement of ions across the membrane , but as it cannot be transferred across the gap between neurones a transmitter substance is released by the pre-synaptic action potential (previously generated action potential) and is used to diffuse across the gap and generate a new action potential at the postsynaptic neurone (the receiving neurone).
voltage gated sodium ion channels
further along the membrane are more sodium ion channels, however the gates on these channels are opened or closed by changes in the voltage across the membrane . the movement of the sodium ions cause the potential difference of the membrane to be reduced , causing the gates to open and more sodium ions to enter the membrane at that point further along. This means that the action potential has moved along the membrane
the myelin sheath
an insulating layer of fatty materials in Schwann cells along the neurone that prevent the diffusion of ions out of the neurone along the majority of its structure, the gaps in the cells are called the nodes of ranvier . the sheath ensures that the ionic movements that create action potential can only occur at the nodes of ranvier. in myelinated neurones the local currents are longer and sodium ions diffuse from one node of ranvier to the next, the action potential appears to jump from one node to the next in a process called saltatory conduction and speeds up the transmittion of action potential , myelinated neurones can conduct action potential at a rate of approximately 120ms
the synaptic knob
the synaptic knob (yes i know the names amusing) is a swelling in the end of a pre-synaptic neurone , it contains a variety of specialized features that allow it to perform its function (for examplemany mitochondria to generate large amounts of ATP ,a large number of smooth endoplasmic reticulum for protein synthesis , vesicles of transmitter substance (for example acetylcholine) and calcium ion channels to trigger the release of the transmitter substance via the vesicles.
the post synaptic neurone's surface membrane contains sodium ion channels for the receiving of the transmitter substance, the shape of the channle is always complimentary to the transmitter used in order to ensure that stray molecules from another type of synapses trigger the transmittion.
there is also an enzyme usualy found in the synaptic cleft (in the case of a cleft that uses acetylcholine, acetylcholinesterase) to breakdown the leftover transmitter substance in the cleft back into its basic components, which are then re-absorbed into the pre-synaptic neurone and re-synthisised by the smooth endoplamic reticulum using energy from the mitocondria into the transmitter substance
a disk arc shape that is around 2-10UM (micrometers long )
each chloroplast has a dual membrane called a chloroplast envelope, there is a gap approximately 10-20NM wide between the inner and outer membranes
outer membrane is permeable to many small ions and the inner is one less so but it contains transport proteins, it becomes folded in on itself to form stacks called granum, between these grana are intergranal lamellae
stroma have a fluid filled matrix. the reactions of the light independent stage of photosynthesis occur in the stroma where the necessary enzymes are located
granum are made up of flattened membrane compartments called thylacoids , they are the site of light absorption and ATP synthesis in the light dependent stage
the transport proteins in the inner membrane control the access of substances into the stroma and cytoplasm
the grana provide a large surface area for photosynthetic pigments , electron carriers and the ATP synthase enzyme
the photosynthetic pigments are arranged into photosystems to to allow for maximum light energy absorption
proteins embedded in the grana hold the photosystems in place
the stroma contains the enzymes needed to catalyze the reactions of the light dependent stage , the grana is surrounded by the stroma so the products of the reactions in a granum can readily pass into the stroma for the light dependent stage
chloroplasts can make some of the proteins needed for photosynthesis using instructions contained in the chloroplast DNA
the combining of ADP and a Phosphate
Group in the Presence of light . the energy is
generated by the exiting of an electron through
light absorbsion. the electon is always returned to its starting point in photosystem 1 at the end of the
cycle (hence the term cyclic photophosphorilation)
the cycle is used by a chloroplast to generate ATP
in cyclic photophosphorilation there is:
the stages of cyclic
1. the exited electron is picked up by an
2. its then passed down by an electron transport chain
3. energy is released in small amounts from the electron to pump hydrogen ions across the thylakoid membrane, building up the concentration gradient
4. the hydrogen ions diffuse back out of the thylakoids through channels attached to an enzyme called ATP synthase
5. this movement generated the energy needed to combine ADP with Pi to create ATP
stages of transmition across the synapse
an action potential arrives at the synaptic knob
the voltage gated calcium ion channels open due to the change in polarization
calcium ions diffuse into the synaptic knob
the calcium ions cause the vesicles to fuse with the membrane causing exocytosis and the release of the acetylcholine molecules
the acetylcholine molecules diffuse across the synaptic cleft
the molecules then bind to the receptor sites on the sodium ion channels in the post synaptic membrane
this causes the sodium ion channels to open allowing sodium ions across the post synaptic membrane into the post synaptic neurone
a generator potential is created , if enough generator potentials combine
endocrine glands : ductless glands that produce and release hormones straight into the bloodstream
exocrine glands : glands that have a long tube to carry a secreted substance (not hormones) to another place (e.g. salivary glands)
target tissue : the cells that possess the specific receptor on the cell surface membrane that are complimentary to that of a secreted hormone
the endocrine system
protein and peptide hormones and derivatives of amino acids : are insoluble in the phospholipid layer , do not enter cells so instead bond with complimentary surface receptors and activate a secondary messenger inside the cell
steroids : pass through the cell membrane and enter the cell to directly effect the DNA in the nucleus
Two types of hormone
is an amino acid derivative (protein based hormone) so it is unable to enter the cell directly , so it reacts with receptors on the cell surface membrane that are complimentary to it , this cause a release of an enzyme called adenyl cyclase which converts ATP to cAMP inside the cell . The cAMP is a secondary messenger as it causes effects inside the cell by activating enzyme actions.
by Sean Scully (scullerz)
investigating factors that effect the rate of photosynthesis - practical
background on indicator solutions
hydrogencarbonate indicator solution is sensitive to small changes in PH , its red when neutral, yellow when PH6 and purple above PH7 , so can be used to indicate when photosynthesis is occurring as...
- yellow shows respiration is occurring as CO2 is being given out and as its mildly acidic it changes the color of the indicator to yellow
- purple shows the taking in of CO2 in photosynthesis as the CO2 loss is making the solution more alkaline ,change in absorption divided by time taken can be used to calculate the rate of CO2 uptake.
practical summery - how these solutions can be used to measure the effect of light intensity on photosynthesis
the plant cuttings should each be place in separate numbered beakers containing identical quantity's of hydrogen carbonate indicator solution
the beakers should then be placed at different distances away from a light source (e.g. a lamp)
the distances should be measured and the light intensity calculated and recorded (1 divided by the distance away in Meters squared )
the lamp should then be turned on and the time taken for each jar to turn purple recorded
this shows how the various degrees of light intensity effect the rate of photosynthesis
other way that this practical could be adapted....
multiple lamps could be used with different colored filters to see the effects of different light wavelengths on the rate of photosynthesis (note distance from the lamps would have to be kept the same as would temperature and amount of indicator e.c.t.).
different beakers could be used with different water temperatures in to see if temperature has any effect
different amounts of powders that add carbon dioxide to the water could be added in i order to test to see how CO2 concentrations effect the rate of reactions
factors that affect the rate of photosynthesis experiment 2
another way to measure the rate photosynthesis is by measuring the amount of oxygen that's released from the plant during its photosynthesizing , one way of doing this is with apparatus called a photosynthometer to capture the oxygen emitted from the plants leaves whilst immersed in water , the device has a way of measuring the length of the trapped bubble (usually some type of ruler) , this measurement can then be multiplied by pi to calculate the area of the bubble.
the steps on how to conduct an investigation into how the rate of photosynthesis is effected by light intensity
fill the apparatus and water bath (add thermometer to water bath and record temperature) with water by removing the end of the syringe and filling with tap, then replace syringe plunger
add pond weed cutting to test tube and immerse in water bath , ensure its the point within the beaker furthest away from your light source to ensure the bath acts as a heat shield
place light source at set distance turn on light source (record the distance and use it to calculate light intensity (1 divided by the distance away in Meters squared )), wait until bubbles start to appear then start timer
when your set time is complete record bubble length, then empty the capillary tubing and re-fill (ensure that there are no air bubbles)
move light source to next location and repeat
when all your results are complete calculate the volume of each bubble and record
the pancreas is both an exocrine gland and an endocrine gland.
the majority of the pancreas consists of enzyme producing cells arranges into acini (singularly known as acinus). the cells produce enzymes used in the digestive system (amylase , trypsinogen and lipase), and sodium hydrocarbonate to neutralize stomach acid. the enzymes are released into various ductules that combine to form the pancreas duct that carries the enzymes into the small intestine
in between the exocrine tissue are patches of the endocrine tissue. these are known as the islets of Langerhan and they consist of Alpha and beta cells, the alpha cells manufacture and release glucagon directly into the bloodstream (used to increase blood glucose concentrations), the target cells for this hormone are in the liver (hepatocytes). and the Beta cells manufacture and release Insulin (used to decrease blood glucose concentrations) , the target cells for insulin are in the liver (hepatocytes), muscle and various other body cells including the brain. these cells also monitor the blood glucose concentrations and detect any changes that occur and release the corresponding hormone to counter it.
for example... if blood sugars become too low
if blood sugar levels were to drop the change
would be detected by receptors of the alpha cells,
beta cells would stop producing insulin and and alpha cells would be stimulated to release glucagon directly into the blood stream , where it would be transported to the liver where it would bind with complimentary receptors in the membranes of there target cells, this would activate adenyl cyclase to produce cAMP which acts as a secondary messenger inside the cell . this stimulates glycogen to be converted into glucose and increases the conversion of fats and amino acids into glucose
but if they become too high....
the glucose acts as a stimulus to cause the release of insulin from the beta cells , the insulin is released into the blood stream and is transported to the liver where it binds with its complimentary receptor on the membrane of the target cell. the insulin causes cells in the liver to absorb glucose from the blood and convert in into glycogen for storage , it also increases the use of glucose in respiration and and inhibits the conversion of fats and glycogen into glucose in muscle and fatty tissue cells
normally , inside a Beta Cell
membrane potential inside is stable at 60-70mv
calcium ion ion channels remain closed
potassium ion channels are open
so K+ diffuses out of the cell
at high glucose concentrations....
glucose diffuses into the cell and is used in a respiration reaction to manufacture ATP
the potassium ion channels close in response to an increase of ATP concentration to stop potassium ions leaving the cell
concentrations of potassium ions inside the cell increase , this causes the cell membrane to begin to depolarize
as the membrain potential rises to -30mv, the calcium ion channels open allowing calcium ions into the cell, this causes the vesicles containing insulin to fuse with the plasma membrain, releasing insulin into the blood stream .
resources used in construction :
My own Class notes
OCR biology textbook
My revision notes OCR A2 Biology revision guide
various internet sites (e.g. google images and some Wikipedia pages) for pictures
the amazing people at crashcourse concourses YouTube : https://www.youtube.com/user/crashcourse
diabetes mellitus is an inability to control blood glucose concentrations , there are two types of diabetes:
type one diabetes
type two diabetes
is caused by inactive beta cells,
normally due to an auto immune
response (the immune system
accidentally destroying the cells) or
caused by liver cells being less
responsive to insulin often due to
ether obesity or high level of sugars
in the diet, though occationly due to
Hyperglycaemia - When a persons blood glucose concentrations are too high
hypoglycaemia - when a persons blood glucose concentrations are too low
respiration is a series of chemical reactions that take place in all living cells .
the reactions release energy from large organic molecules in a controlled fashion so that it can be utilized to create ATP.
many functions within all living cells require an immediate energy source, this is often provided through the Use of ATP , which is produced by respiration
introduction to respiration
Definitions to remember !
organisms that convert small inorganic molecules into large organic molecules
organisms that breakdown large organic molecules into small inorganic molecules and releasing the energy stored within
reactions that build up small molecules into larger ones
reactions that break down large molecules into small ones
all the chemical reactions that occur within a living organism
"energy exists as potential stored energy
or kinetic energy"
ocr biology textbook
autotrophs create there own energy in the form of large organic molecules whilst hetrotrophs canott produce there own energy so have to consume autotroph's in order to aquire the large organic molecules needed
living organisms need energy for
replication of DNA and organell synthisis
activation of chemicals
"energy cannot be created or destroyed but is transformed from one form to another"
chemical potential energy
in organic molecules
consumers and decomposers
(e.g. animals, fungi and most
CO2 + H2O
(e.g. plants , some
protoctists and bacteria
catabolism (see catabolic) - reactions that break down molencules (e.g. digestion and respiration)
anabolism (see anabolic) - reactions that build up molecules (e.g. photosynthesis , nucleic acid, protein and polysaccaride synthesis)
is a Phosphorylated Nucleotide ( in other words its a nucleotide made of a phosphate sugar and an organic base!)
its breakdown provides the immediate source of energy for biological processes , energy is released in slow burst to ensure that it doesn't damage the cell
control of heart rate in humans
the heart can supply additional oxygen and nutrients to various parts of the body by....
increasing the number of beats per minute
the strength of contractions
the volume of blood pumper per heartbeat
this is controlled by both hormonal and nervous systems . whilst the heart is capable of generating its own rhythm (myogenic) , these impusles are overridden by The sinoatrial node (SAN) which acts as a pacemaker. The SAN generated waves of exitation that causes the heart to beat, the rate at which it initiates contractions is down to two nerves from the cardiovascular center in the medulla of the brain, these are:
The Vagus Nerve ( the decelerator nerve) which releases acetylcholine which slows the heart rate
The accelerator nerve releases noradrenaline, which is similar to adrenaline and increases heart rate
the nerves also affect the atrioventricular node (AVN). the heart will also responded to certain hormones in the blood in particular adrenaline
movement of limbs
Reduced blood plasma PH from excess Co2
Higher Blood pressure
stretch receptors in muscles
increased heart rate as
increased respiration is needed
chemoreceptors in the carotid arteries aorta and brain
increased heart rate so
CO2 is removed faster
stretch reseptors in walls of
the carotid sinus
reduces heart rate so blood
pressure can start to drop
ATP consists of:
Adenine (an organic base
ribose sugar (the same sugar used in RNA)
Three Phosphate groups
when the phosphate groups are removed energy is released leaving ADP
are complex organic molecules that contribute to enzyme controlled reactions by transporting the end products from one reaction to the start of another reaction.
Respiration is a complex series of reactions and the co-enzymes are used to link a number of these reactions (Not all of them note)
some of the co-enzymes used in respiration include:
NAD which is reduced by hydrogen atoms released from the respiratory substrate (the substrate that's broken down to produce ATP (usually glucose from carbohydrates as this is the preferred material to be used)) . the hydrogen atoms are used to power an electron transport chains (found in the mitochondrial cristae) used in ATP production when oxygen is available. however when oxygen is unavalible, the atoms are used to reduce pyruvate to lactase in anaerobic respiration
Co-Enzyme A binds to a two carbon acetate group in the link reaction and then delivers the acetate group into the Krebs cycle
"the process whereby energy stored in complex organic molecules is used to make ATP"
a molecule that's broken down in order to release energy in respiration, examples of the types of molecules used are shown below
carbohydrates: the primary molecules used in respiration and the first choice molecule to be used in respiration, there converted into glucose before they enter the respiratory pathways, some cells (e.g. brain cells) can only process glucose
Fats : the second choice molecule to be used in respiration , if no / little glucose is available . they contain large numbers of Hydrocarbon bonds so many hydrogen atoms are produced when there broken down so large amounts of the NAD can be reduced , producing large amounts of ATP, carbon atoms are also produced
Proteins : are broken down into amino acids that are then de-aminated , the remaining residue can then be entered into the Krebs cycle at an appropriate place (as each amino acid will differ slightly). each amino acid will produce a slightly different yield of ATP but overall this yield is similar to that of carbohydrates
the four stages of respiration- an overveiw
glycolysis- occurs in the cytoplasm of the cells and is the stage that dosnt require oxygen. during glycolosis glucose (6C) is broken down into two pyruvate (3C), a net of two ATP are produced and 2 NAD reduced
The link reaction - occurs in the matrix of the mitochondria. two pyruvate molecules are dehydronated to produce 2 carbon acetate that bond with Co-enzyme A , hydrogen atoms that reduce NAD and carbon dioxide
the Krebs cycle which takes place in the mitochondrial matrix
oxidative phosphorylation- the folded inner membrane is phosphorylated to ATP
a total of 26 ATP molecules are produced (10 reduced NAD)
(for more details on each stage see the next few slides/pages (whatever you call them on prezi)
Glycolysis (Latin for "splitting sugar"),
its the breakdown of glucose into smaller three carbon chain molecules called pyruvate .this reaction occurs in the cytoplasm of the cells and does not require oxygen so is an anaerobic process, but occurs in aerobic respiration as well.
the reaction chain of the breakdown of glucose occurs as follows:
the glucose undergoes phosphorylation (two phosphate groups from ATP are added to "activate it") to produce hexose bisphosphate
the hexose bisphosphate is gradually split using ATP into two triose phosphate (TP) molecules ,
triose phosphate is the oxidises to produce Pyruvate , this is done by the removal of hydrogen atoms (this hydrogen is then used to reduce NAD) , this also allows the production of some ATP through substrate level Phosphorylation (an enzyme is used to create ATP through combining of ADP and a phosphate group using energy released from the substrate molecule)
the structure of mitochondria
the ultra structure of mitochondria consists of:
an inner and outer membrane separated by an inner membrane space
the outer membrane is smooth and contains a number of receptors and a number of carrier proteins to allow molecules such as pyruvate to enter and leave the mitochondria. any other protines found in the membrane are enzymes
the inner membrane is folded into organelles called cristae (singularly crista) , these are composed of a different variety of lipid to that used in the outer membrane and is therefor impermeable to most small ions (e.g. hydrogen), the inner membrane also contains a large number of carrier proteins that form electron transport chains.
Each electron carrier is an enzyme that is assosiated with a certain co-factor
the mitochondrial matrix is a gel-like substance enclosed within the inner membrane , this is where the Link reaction and the Krebs cycle occur. it consists of a mix of proteins and lipids. it also contains looped mitochondrial DNA to code for the enzyme and other proteins , Mitochondrial Ribosomes where the proteins are assembled, and Enzymes used to catalysis these reactions and there Co-enzymes (e.g.NAD).
communication and Neurones
excreation is the removal of metabolic wastes from the body
metabolic wastes consist of waste substances that may be toxic or are produces in excess by the reactions inside a cell
if carbon dioxide is left to build up within the body it can become toxic and cause a number of negative effects , for example it can react with water within the body to form carbonic acid that can disrupt the rate of enzyme reactions. the CO2 can also reduce the affinity for oxygen of hemoglobin , meaning that oxygen transport potential is reduced in the blood. it also causes H+ ions from the Carboxyhaemoglobin reduce the PH of the blood, this is detected by receptor cells in the medulla oblongata , this attempts to reduce the Co2 in the blood by increasing the breathing rate of the Affected. if this continues to when a persons PH is below 7.35 it causes respiratory acidosis, .
CO2 is removed from the body by the following system :
Carbon dioxide is removed from the cells via diffusion
it enters the blood where its transports to the alveoli in the lungs
through gaseous exchange, the carbon dioxide diffuses into the airspace of the alveoli
ventilation expels the carbon dioxide from the lungs
made in the liver
Break down of amino acids (De-animation)
Transported in blood plasma
kidneys remove urea and forms urine
stored in the bladder and excreted via the urethra
this happens because the body cannot store proteins , but as it would be wasteful to secrete them the body De-animates them
amino acid + oxygen keto acid and ammonia acid
keto acid is used in repiration or convered into storage substances (fats and carbohydrates)
toxic ammonium is converted into less toxic urea
ammonia + CO2 urea + water
electron transport chains
in the inner membranes of the mitochondria there are a number of electron carriers that are arranged in electron transport chains , each electron carrier is an enzyme that is associated with a specific co-factor ( a non-protein group), in this case a haem group containing an iron atom.
these co-factors accept electrons from one electron carrier and will then donate them to another electron carrier further along the electron transport chain. some of the enzymes have a co-factor that that uses energy from passing electrons to pump protons into the membrane space , where they collect due to the lipids property's to block small ions , to form a proton gradient , a potential energy source.
ATP synthase enzymes
Proton's flow down the concentration gradient through the ATP synthase Enzymes from the intermembrane space into the mitochondrial matrix. (this is a form of Chemiosmosis) . the movement of this force rotates part of the enzyme , and allows ADP and Pi to be combined to create ATP.
The link reaction
when sufficient oxygen is available for aerobic respiration to take place, pyruvate is actively transported into the mitochondria. the link reaction takes place in the mitochondrial matrix.
dehydronase of the pyruvate is the first stage to occur, this is the removal of the hydrogen atoms via dehydrogenate enzymes
decarboxylation then occurs , this is when the pyruvate is broken down to produce a 2 carbon acetate and carbon dioxide (which is then later excreted)
NAD is the reduced by the Hydrogen atoms released from the pyruvate
the remaining substrate (acetate) is then combined with co-enzyme A to produce acetyl co-enzyme A to carry the acetate to the next stage.
overall a net of two ATP are produced (two are used up at the start of the reaction) , two reduced NAD are produced and two molecules of pyruvate are produced
mitochondria are "rod shaped" or "thread like" , there between 0.5-1.0 micrometers in diameter and 2-5 micrometers long. mitochondria can be moved around cells by the cytoskeleton.
the krebs cycle takes place in the mitochondrial matrix
the steps of the krebs cycle is as follows
acetate is released from from the acetyl co-enzyme A and is combined with a 4 carbon compound (oxaloacetate) to form a 6 carbon compound (citrate) . the co-enzyme A is released to be used again.
the cirtane then enters a cycle of reactions to release the chemical energy it contains.
the citrate is then decarboxylated and dehydronated to re-form oxaloacetate (the decarboxylation form more CO2 which is excreted and dehydronation produces more hydrogen ions to reduce NAD and FAD , which pass them on to the next stage).
during the Krebs cycle , some ATP is produced by substrate level phosphorylation, which is where ADP and Pi are combined by an enzyme using energy from the substrate molecule.
Oxidative Phosphorylation and chemeosmosis
this literally means the addition of a phosphate group in a process that uses oxidation/ reduction reactions. in this case this is the phosphorylation in ADP in the presence of oxygen (the final electron carrier). the mitochondrial cristae is where the reduced co-enzymes carry the hydrogen atoms they've collected from the various stages of the aerobic respiration cycle , there are electron carriers embedded in the inner membrane, the first carrier in the chain, known as NADH dehydrogenase, oxidised the reduced co-enzyme by removing the hydrogen atom and splitting it into a proton and an electron. the co-enzyme is then released and returned to the mitochondrial matrix to accept more hydrogen atoms. the proton is also sent to the mitochondrial matrix for use in chemeosmosis (see next slide) . the electron is passes down the electron transport chain and as its passed between carriers, energy is released.
chemeosmosis is the process involving the creation of a proton gradient through the action of an electron transport chain and the use of the proton motor force to produce ATP.
the energy released from the electron as it procedes down the electron transport chain is used by several channel protines to pump protons from the mitochondrial matrix into the space between the mitochondrial membranes, the protons cannot pass through the specialized lipids that make up the membranes and so begin to collect, forming a proton gradient ( a change in PH and potential difference across the membrane also occurs) . The proton gradient and the potential difference creates a driving force ,called the proton motive force, which pushes the protons into the mitochondrial matrix. As the protons can only pass through channel protines in the ATP synthase enzymes, the movement energy they produce is used to combine ADP with an inorganic phosphate group (Pi) to create ATP. The protons then return to the matrix where they combine with oxygen to form water (this makes oxygen the final electron acceptor in aerobic respiration).
Oxidative Phosphorylation and chemeosmosis
Experimental evidence for Chemiosmosis
Yield Of ATP
each reduced NAD enzyme contains enough energy to produce approximately 2.5 ATP molecules , and each reduced FAD enzyme 1.5 ATP molecules , so approximately 30- 34 ATP molecules are produced per glucose molecule (best to put 32 to be on the safe side, 4 from the the initial glycolosis stage and 28 from the oxidive phosphorylation/chemiosmosis stages !)
diagram of Oxidative phosphorylation
functions of the liver
storage of excess glucose as glycogen for if blood sugars get too low
Detoxifying of alcohol
production of Bile for use in the breakdown of Fats and lipids
split into three lobes
three blood vessels are linked to it, the aorta brings oxygenated blood from the heart as the liver is highly metabolically active organ so needs a high oxygen intake for respiration. The Hepatic portal vein brings deoxygenated blood from the digestive system , this is normally rich in excess glucose and other food substances that need to be filtered out and then broken down. The Bile duct collects the bile produced by the hepatocytes and sends it to the stomach where its used to break down fats and lipids
the smaller sections of the liver are known as lobiels , these contain two types of vessles , inter lobial vessels (which are found between lobiels) and intra lobial vessels (which are found within lobiels)
Anerobic respiration is the release of energy from substrate molecules without oxygen
, it takes place in the cytoplasm of cells. As the electron transport chain cannot function without oxygen, and the Krebs cycle and Link reaction cannot operate , the only way the body can produce ATP is through Glucolosis. there are two methods that eukaryotic cells use to anaerobically respire.
1) mammals body cells use lactate fermentation, this normally occurs in there muscle tissues during moments of intense exersize when ATP demand is high and oxygen concentrations are low. in lactate fermentation...
the pyruvate produced in glycolosis is reduced into lactate through the use of hydrogen atoms( from reduced NAD also produced in glycolosis) and the enzymen lactate Dehydrogennase
this reoxidises the NAD so it can return to the glycolosis stage and pick up more hydrogen atoms
the lactase is transported to the liver , where it is stored untill oxygen is available at which point it is converted back into pyruvate and entered into the krebs cycle or link reaction
2) yeast cells perform Alcoholic fermentation when no oxygen is available, in alcoholic fermentation...
the enzyme Pyruvate decarboxilase is used to remove a molecule of carbon dioxide from the pyruvate, creating the substance ethanal, the enzyme ethanol dehydrogenase is then used along with two hydrogen atoms (again from reduced NAD from glycolosis) to create the waste product ethanol.
yeast are a facilitate anerobe , they can survive on anaerobic respiration but are killed if the waste product of ethanol builds up to over 15%
The structure of Liver
intra lobial vessel
inter lobial vessels
as blood passes through the liver it gets cleaned and detoxified and then sent back the heart, blood from the aorta and portal vein mix in the sinusoid channels.
Bile ducts run in the opposite direction to the blood channels.
endothelial cells break down red blood cells.
i apologize, this is me being a bit lazy
laptop crashed in class and as my answer
got good marks i just scanned it in and posted
it , if anyone has trouble reading this , drop a
comment in the comment section and ill re-type it up on the prezi instead for you
the genetic code
a sequence of neucleotides that code for one or more polypeptide.
there are approximately 25000 genes in the human genome
most genes are found within the chromosomes in the nucleus , though some are found in the mitochondria.
genes code for polypeptides such as haemoglobin , collagen and kerotin, antibodys and antigens
a chromosome is a single molecule of DNA and are associated with histone proteins which DNA winds around
a code formed by the sequence of nucleotides in a gene
a sequence of three neucleotide bases codes for one amino acid (these are called triplets)
the number of triplets indicates the number of amino acids in the polypeptide
the sequence of triplets indicates the sequence of amino acids in a polypeptide
its a degenerate code meaning that all amino acids (exept for methionine) has more than one code
some codes dont code for an amino acid, but indicate "stop" at the end of a chain
the gene to be transcribed unzips , this is done by braking the hydrogen bonds between the nucleotide bases, note that only the template strand of DNA is used and not the whole DNA molecule unzips , just the gene in question
activated RNA molecules bind with there complimentary base pairs (U with A , G with C , A with T) , the energy from two released phosphate groups provide the energy for this process along with help from the enzyme RNA polymerase, this also binds the adjacent nucleotides together
the PremRNA produced is complimentary to the template strand of DNA, and is therefore a copy
the premRNA undergoes splicing to remove interons, forming mRNA and Exons
the mRNA is released from the nucleus through a pore in the nuclear envelope , to a ribosome
each nephron starts at the cortex of the kidney at a glomerulus, surrounding the glomerus is a structure thats known as a bowmans capsual (this is where ultrafiltration occurs ) which passes fluid to the proximal convoluted tubule where selective re-absorption takes place, which begins to alter the composition of the fluid as its passed along the nephron. the fluid is then passed through the loop of henle, down into the medulla and back out to the cortex. from the loop the fluid passes into the collecting duct where water absorption takes place and the final product (urine) is passed on to the next stage.
formation of urine part one: ultrafiltration
ultrafiltration is the filtering of the blood through a basement membrane that acts like a fine sieve.
the first stage of ultrafiltration is blood flowing into the glomerus from a different arteriole (this is wider than the efferent arteriole which carrys blood away from the glomerus )
the different sizes ensures that blood within the confines of the glomeus is under increased pressure, and that that pressure is higher than the pressure within the bowmans capsule so that blood plasma from the blood is forced into the bowmans capsule
the bowmans capsule has a layer of cells known as podocytes, they have primary processes and secondary processes (they look similar to fingers or cillia) , that ensure there are gaps between the cells that allow fluids to enter the capsule, between the glomerus and the podocytes is the basement membrane that filters out any molecules with a relative molecular mass of 69000 or less.
the blood proteins and cells remain in the capillary and the low water potential enesures some of the liquid remains and that water is re-absorbed at a later stage.
formation of urine part 2: selective re-absorption
this is when specific substances are removed from the tubule to be absorbed into the blood, leaving other substances behind. the cells that make up the proximal convoluted tubule are designed to re-absorb glucose, amino acids and mineral ions from fluids within the tubule so 85% of selective re-absorption occurs in the proximal convoluted tubule.
the cell membrane that's in contact with the tubule are folded into microville , the membrane also contains specialized sodium ion channels that transport sodium ions that are coupled with an amino acid or glucose molecule from the cell into the bloodstream along with some water, via active transport using energy from mitochondria, this creates a concentration gradient as the amount of substances inside the cell decreases , forcing substances inside the proximal convoluted tubal to be drawn towards the cell, when sodium ions within the tubal come into contact with the microville on the membrane on that side a transport enzyme links them with a molecule of amino acid or glucose so that they can then be carried across the membrane through specific channels, into the cell, then the cycle repeats.
this is the control of the water potential of the blood by negative feedback, the osmorecetors in the hypothalamus of the brain detect a change in the water potential of the blood, they do this by absorbing water via osmosis when water potential is high causing them to expand, whilst when water potential is low the shrink via osmosis. then, depending on the nature of the issue, they adapt the ADH release from the posterior pituitary gland (greater release if water potential is low, less is water potential is high) to change the permeability of the collecting duct walls , so that they become less permeable if water potential is high so more water is removed from the body as absorption into the blood is reduced, and more permeable is water potential is low so more water is re-absorbed into the blood and the blood water potential is increased.
the thickness of the collecting duct is changed by the cell receptors in the cell membranes detecting the ADH and releases cAMP into the cell as a second messenger, the result of this
formation of urine part 3: The loop of henle and water re-absorption
the role of the loop of henle is to create a low water potential in the tissue of the medulla for water to be absorbed from the fluid in the collecting duct, this is done by salts being moved into the descending limb of the loop of henle from the ascending limb via diffusion , this causes some water to be removed from the descending limb and transported by osmosis to the blood as the water potential is low outside of this area of the loop due to the salt storage. as the loop begins to ascend ,at the base of the ascension the sodium and chloride ions diffuse out by diffusion but as it goes higher active transport is required to remove them from the fluid,some of the salt is then moved into the medulla where it will cause water to be removed from the collecting duct via osmosis (the amount of water removed depends on the permeability of the duct (see osmoregulation)) into the surrounding capillary's, some will be transported back to the descending limp of the loop and the cycle repeats.
only about 1.5-2.0dm3 of fluid actualy reaches the pelvis via the collecting duct each day, and has a very low water potential and high concentrations of urea and salt.
natural clones: plants
many plants are capable of reproducing asexually through a process known as vegetative propagation.
methods of vegetative propagation include-
producing runners or stolons that grow along the surface or just below the ground, occasionally these horizontal stems take root and grow a new stem that can split off and become an individual plant (e.g. strawberry and spider plants)
root suckers or basal sprouts which act like runners but are when a plant propagates new stems along its roots, this occurs usually due to damage or illness of the parent plant. one example of this is dutch elm trees produce root suckers which has helped them to survive dutch elm disease , when the parent plant is killed by infection
bulbs and tubers, which spend winter underground , examples include many potatoes being produced from a single potato plant or a patch of daffodils growing from one daffodil bulb
artificial cloning in plants
introduction to biotechnology
"biotechnology is technology based on biology and involves the exploitation of living organism or biological processes, to improve agriculture , animal husbandry , food science , medicine and industry"
OCR biology Textbook
here are several examples of uses of biotechnology
processing food - whole microorganisms are used in making cheese, yoghurts ,bread, beer e.c.t , quorn is created by in cultures and the mycelium produced is separated and used in food, naturally brewed soya sauce is created is by roasted soya beans being fermented by yeast or a fungus
producing medicinal drugs - penicillin is produced by the fungus penicillin as a bi-product of its metabolism , some genetically modified mammals can also produce useful proteins that are harvested in there milk
production of enzymes and chemicals for commercial use - methanogenic bacterium raised on sewage can produces gases that can be used as bio fuel
treating of waste products - water waste treatment involves the use of bacterium that break down sewage and use it as nutrients, and as a result renders the waste harmless, some natural pesticides use microorganisms that are designed to target a specific organism. genetically modifying crops to be resistant to certain pests and diseases is also a form of biotechnology
biotechnology of today
biotech of today involves reaserchers taking a single gene from a plant or animal cell and inserting it into another plant animal or bactirium of a different species. (e.g. transferring jellyfish genes into mice so that they glow)
modern biotechnology also allows the modifying of a gene to produce a different protein.
risks are assessed before experiments are conducted
how readily organisms could cross breed with similar organisms in the environment
weather the modifications give them any advantages over other organisms in an environment and upset the balance of the ecosystem
the different types of microorganisms are - bacterium, virus, Fungi, protozoa ,
the advantages of using microorganisms in biotechnology are:
they grow rapidly, even at low temperatures
they reproduce quickly and asexually so individuals are genetically identical
they remain as single cells or as small cell clusters so they don't differentiate and remain productive
often produce proteins or chemicals such as toxins that are excreated into there external environment, and then isolated and extracted in a pure form, which lowers processing costs
they can often be grown using substances that are considered to be useless or even toxic to humans
they can also be grown in almost any climate
they can be genetically engineered to produce specific products
why use microorganisms
advantages and disadvantages of Asexual reproduction and vegetative propagation
allows an organism to reproduce quickly and take advantages of resources that are available in the environment
can be completed under circumstances where sexual reproduction will fail or is impossible
all offspring will have genetic information that will help them to survive in there current environment.
in the case of plants they allow for survival of the plant offspring in times of stress or injury in the form of a clonal patch.
as the new organism has identical DNA (and as a result , identical genetic weaknesses) to that of the parent plant, any changes in the environment will effect the new organisms as much as the parent. (e.g. the way that elm trees produced by root suckers from a tree with dutch elm disease are likely to die from the same disease as theirs no chance for natural selection to occur)
lack of genetic variation
there are many ways of artificially cloning plants, for example....
grafting which is when a shoot section of a woody plant such as a fruit tree or rosebush is joined to an already growing root and stem section (known as a rootstock) the graft grows and is genetically identical to the parent plant , but the rootstock is different
many species of plant are capable of reproducing by fragmentation , this is when a small part of a plant regenerates to become a whole plant, many gardeners and botanists will increase the number of plants they own by exploiting this useful ability. this is done by taking a "cutting" (a removed branch or stem) and placing the cut end into the ground , where they may sprout roots and begin to grow. the success rate can be improved using rooting powder which contains auxin , a plant growth regulator hormone.
mass cloning of plants is often done using micropropogation, which is when a small piece of tissue is taken from a parent plant, usually from the shoot tip this tissue is known as a explant , the explant is placed in nutrient growth medium , such as agar gel , where the cells will divide but wont differentiate, forming a ball of undifferentiated cells called a callus, the calluses can be removed after a few weeks , then places in a medium that encourages stem growth, then after a few weeks there, in a medium that encourages root growth. after this the now growing plants are transferred to a greenhouse and allowed to acclimatize before being planted outside.
advantages and disadvantages of plant cloning in agriculture
much faster than selective breeding
allows valuable plants or those with specific property's to be replicated precisely
all the plants will have the same genetic structure meaning there easier to harvest
infertile plants such as triploids can be replicated
plants such as orchids that are hard to grow from seeds can be replicated.
(see disadvantages to asexual reproduction, as they are pretty much identical)
some methods of cloning ,such as creating cell cultures on a large scale, is very expensive.
microorganism culture is a growth of microorganisms , this can be a pure culture (one species) , or a mixed culture (multiple species)
there are liquid cultures ( a broth) or solid cultures (nutrient agar)
standared growth curve - when microorganisms grow in an environment where conditions are fixed (no nutrients are added and no waste products are removed , causing a well established pattern to form. This is also known as a closed culture
plotting the population size over time gives the standard growth curve
there are four phases to the standard growth curve :
lag phase - reproduction and growth are very slow as cells acclimatise,grow, produce enzymes and store energy. this may also involve gene activation to produce enzymes
exponential (log) phase - there is a rapid reproduction rate and cells may divide every 20-30 minutes so the population can double every generation , there are no limiting conditions and few cells die. the length of this phase depends on how quickly the organisms reproduce and take up available nutrients and space
stationairy (stable) phase - the population remains stable as death rate equals the reproductionrate. this is due to the decrease in avalible neutrients and the increase in excreated waste products(in an open system this would be down to the carrying capacity of the enviroment
decline phase - the death rate exeeds the reproduction rate and the population may decline to zero, this is often due to a limiting condition such as high temprature, limited nutriants or oxygen, and a build up of waste products such as CO2 or ethonol.
the growth curve
the greater the number of nutrients at the start of the curve the longer the log phase and the higher the population.
metabolites are the products of metabolic reactions(THESE ARE THE REACTIONS THAT KEEP AN ORGANISM ALIVE! (see your as biology notes (provided you kept them)))
primary and secondary metabolites
primary metabolites = are products produced by an organism as a result of normal metabolism (normal growth). this includes amino acids, proteins, enzymes, nucleic acids, ethanol and lactate. the production of primary metabolites matches the growth in population of the organism
secondary metabolites = are substances produced by an organism that are not part of its normal growth. for example allot of antibiotic chemicals produced be certain microorganisms are secondary metabolites as there designed to reduce competition for food. there production normalcy occurs after the main growth period of the organism and so does not match the the growth in population of the organism
If microbes are given a suitable nutrient medium and the right conditions (temperature, pH, oxygen levels), it is easy to grow them on a laboratory scale in Petri dishes, test tubes and flasks.
Producing substances e.g. penicillin from microbes on an industrial scale causes problems because massive numbers of organisms have to be grown for commercial use.
The microbial culture then has to be separated and treated to produce the final useful product.
The microorganisms are grown in very large vessels called fermenters.
kidney failure normally occurs due to...
renal dialysis - this involves connection of to a dialysis machine which takes blood from a vein in the arm and passes it over a dialysis membrane , this membrane is partialy permeable and exchanges materials between the blood and a special dialysis fluid. the fluid contains all the correct concentrations of various substances found in the blood and needs to be constantly refreshed, over time unwanted substances will diffuse from the blood into the fluid and the blood returned from the fluid into the arm. the disadvantage of dialysis is that the patent will have to spend many hours a week connected to a machine and dietary intake has to be monitored carefully.
transplants - this is when a damaged/failed kidney is replaced with a new one so a patient , a kidney from a family member would be better as its more likely to be genetically compatible can live a normal life, the advantages are that you don't have to be restricted by the need to be connected to a machine twice a day like with dialysis. the disadvantages are that the patient will need to take imunosuppresent drugs for the rest of there life to prevent there immune system from attacking the new kidney.
pregnancy tests - Human Embryos release a hormone called human chlorionic gonadotrophin, which will appear in the urine of the mother. pregnancy testing sticks contain monoclonal antibodys specific to this homone. they are held attached to a tiny blue bead, these molecules are free to move whilst other enzymes are fixed in place in a line across the strip. if the hormones are present they binds the moving antibodys to the fixed enzymes in a line across the strip
anabolic steroid tests - done using gas chromatography , this test is designed to
precise growing conditions depend on the microorganism that are to be grown and whether the process is designed to produce primary or secondary metabolites
temperature - too hot and enzymes become denatured too cold and activity is reduced
substrate or nutrients - the correct nutrients must be added including sources of carbon and nitrogen when these are added depends on the type of culture (batch or continuous) and whether its a primary or secondary metabolite being produced
oxygen - depends of whether the metabolite your after is produced by aerobic or anaerobic conditions
PH - this needs to be maintained to ensure enzyme activity continues as required
Agitation - the culture needs to be continuously stirred or mixed in order to prevent microorganisms sinking to the bottom of the fermenter which would reduce activity and to ensure an even distribution of nutrients
commercial applications of biotech - growing conditions
fermenters are filled with a sterile neutriant solution , which is then inoculated with a pure culture of fungus or bacterium
paddles rotate the mixture and more nutrients can be added
probes monitor the mixture and changes in the PH, oxygen concentration and temperature are all computer controlled
a water jacket surrounds the fermentor in order to keep it cool
cells are grown in a fixed volume of liquid medium in a closed vessel
no microorganisms , fluid or nutrients are added or removed
used for producing secondary metabolites , e.g. penicillin, which are highly unstable and not essential to the growth of the culture
secondary metabolites can be extracted economically only when they reach a high concentration within the culture
nutrients are added constantly and cells harvested at a constant rate
volume of suspension is kept constant
fermenter does not have to be cleaned or re-filled very often
production is almost continuous
continuous cultivation needs sophisticated conditions to maintain constant conditions, and highly trained staff need to operate the equipment, as a result the process is expensive
the nutrient medium used to support a culture of microorganisms can also be used to support many other types of microorganism. any unwanted microorganisms in a culture are called a contaminant
contaminant microorganisms can;
compete with the culture microorganisms for space and nutrients
reduce the yield of usefull products from culture microorganisms
cause spoilage of the product
produce toxic chemicals
kill the cultured microorganisms and destroy there products
in a process where food or medicinal products are being produced , contamination means that the entire culture has to be destroyed as the products have to be regarded now as unsafe
aseptic techniques are the steps taken to prevent contamination of a culture , asepsis is the absence of contaminants in a culture (in other words a uncontaminated culture)
alcohol is stored by the body because it contains potential energy for respiration and can be converted in acetyle co-enzyme A.
negative effects of alcohol
in large quantity's it becomes toxic and cause liver failure or poisoning
acts as a depressant and slows down nerve impulses
because NAD molecules are used in the breaking down of alcohol it means that there not breaking down fats, which then accumulate in the liver , sometimes to levels where the liver fails
low powered tissue plan : G A kidney
revision from AS , enzymes are used as
biological catalysts to speed up the rate of reactions
the enzymes active site is specific to a specific substrate with a complimentary shape
they are a protein with a tertiary structure
they can become denatured by extreme changes in PH or temperature
they are not used up in reactions so are re-useable
the collision theory
anyway with that over back to A2 stuff...
enzymes are a primary metabolite and there for are normally produced in the normal growth of a microorganism, therefor continuous cultures are the best way to produce them.
enzymes are useful in industrial processes due to them being specific to a certain molecule, meaning that fewer by products are formed during a reaction and less purification of the final product is required. the fact that many enzymes are also specific to a certain temperature range can be useful as many operate best at lower temperatures and the fact that they lower the activation energy of a reaction can means that they can save money for a company as they may not have to heat a reaction chamber in order to produce a specific product. some enzymes such as thermophilic enzymes that operate well at higher temperatures can be useful in reactions that need a higher temperature.
sometimes it is more efficient in large scale production, or production that requires a large degree of accuracy, to use just a culture of isolated enzymes rather than a culture of the microorganisms to save the costs of purification of the product and to make the process more efficient.
the extraction of an enzyme from a microorganism culture is known as downstream processing. this can be done to use the enzyme in a product or to use the enzyme to make a product
after production of one batch the product the enzyme can be reused to produce several batches of the product
in order for the enzyme controlled reaction to occur the enzyme and substrate must be allowed to collide. but its also possible to immobilize the enzyme so it dosent mix freely with the substrate meaning that it can be re-used and dosent have to be extracted from the final product , this is done bu attacking the enzymes to an inert surface (such as plastic beads or clay particles).
enzymes do not contaminate the product
easier to seperate enzymes and products
allows it to catalyse in unfavorable mediums
increases stability and can be manipulated easily
allows enzymes to be reused
may alter the enzymes shape
may alter there catalytic ability
enzymes may become detached
methods of immobilizing
a) absorption - enzyme molecules are mixed with an immobilizing support and bind to it due to hydrophobic reactions and ionic links. this can give high rates of success though it is possible due to the bonds being weak for enzymes to become detached
b) covalent binding - enzymes are covalently bonded to a support, often including linking enzymes together and to the support using a cross linking agent. this is hard to do to a large quantity of the enzyme but the bonding is very strong
c) entrapment - enzymes are trapped in gel beads or a network off. the substrates need to get through the net to the enzymes which can slow reaction rates more than with absorption or covalently bonded enzymes.
d) membrane separation - enzymes are separated from the substrate by a partially permeable membrane. the substrate and products can pass through the membrane but the enzymes cannot
studying whole genomes
DNA profiling/genetic fingerprinting - a technique used by forensic scientists to assist in the identification of individuals based on their DNA
Genome Sequencing - is the identification of the order of DNA nucleotiddes within a genome. therefor what order of the nitrogen bases make up an organism. this is used in the research of gene functions
Genetic engineering - the production of chemicals for the pharmacy industry , agricultural industry and xenotransplantation
Gene therapy - the most controversial and least well developed type of genetic engineering, which is when a human is genetically altered in order to cure a disease. which may allow doctors to cure incurable diseases
genomics : the study of the whole set of genetic information in the form of the DNA bases sequences that occur in the cells of the organisms of a species
human genomic s is the study of the structure and function of the human genome including there genes and there surrounding DNA sequences
there are over 3 billion base pairs in the human genome
only 1.5% is assigned to protein coding ,the rest is known as non coding DNA and a large amount of research is being carried out to establish its functions
this can be used in.....
genetic sequencing - an over view
each DNA sequencing reaction only covers 750 base pairs, meaning that DNA must be broken up and sequenced in sections. sequencing also has to be done a number of times on overlapping code to ensure accuracy and so the overlapping fragments can be re-assembled to form the completed code. the stages of sequencing are as follow
the DNA is extracted and split into fragments of 100,000 neuceotides in length using restriction endonuclease enzymes.
these sections are transferred to a bacterium artificial chromosome (or BAC) and the transferred to a bacterium such as E.coli which are then allowed to grow and reproduce in a culture , creating copys of the DNA.
the DNA is then extracted from the E.coli and split into fragments of up to 1000 nucleotides using various restriction enzymes ,this produces a range of fragments that overlap rather than fragments of the same length.
the fragments are separated by gel electrophoresis , and then sequenced by an automated process. The fragments are then compared to reassemble the whole BAC sequence
DNA consists of...
a double helix structure
contains a phosphate-sugar back bone, attached to a deoxyribose (hexose sugar) molecule bonded with complimentary organic nitrogen bases
there are hydrogen bonds between the nitrogen bases
4 bases A + T and G + C
RNA is composed of...
a single strand
Uracil replaces thymine
the backbone contains ribose instead of deoxyribose
DNA replicates through semi conservative replication (the origonal strands are conserved and new strands are made )
the process used to separate DNA fragments, based on there size, for identification and analysis. The process uses two electrodes and a slab containing a block of agar gel.
the collected DNA samples are firstly treated with a restriction enzyme so that they are cut into fragments of various sizes.
the samples are then places into wells at the negative electrode end of the gel, the gel is then immersed in a tank of buffer solution and an electric current is passed through it for a set period of time
as DNA is negatively charged due to all the phosphate groups it has , its attracted towards the positive electrode, as the shorter DNA strands move faster than the longer electrode strands due to the longer strands getting more caught up in the agar gel. meaning shorter strands will get further towards the electrode in the set time. forming specific bands of differently sized DNA
normally the DNA strands cannot be seen but use of a dye or florescent tags can allow scientists to display there positions.
to lift the fragments from the gel for further analysis a method called the southern blotting is used, this is when a nylon or nitrocellulose sheet is placed over the over the gel, covered in paper towels, pressed then left overnight to allow the fragments to be transferred to the sheet, the DNA will have to be tagged with a radioactive marker before the process begins for it to be visible on the sheet.
this also means that a radioactive gene probe can be used to check for the presence of specific Genes, DNA strands or DNA sequences. this can also be used to create a DNA profile (e.g. crime scene investigations)
used to identify and label DNA fragments that contain a specific DNA Sequence
a probe is a short length of DNA (50-80 nucleotides long) with a label attached
the probes nucleotides are complimentary to the DNA strand that you are looking for.
to label the probes ether radio active markers will be used so the targeted DNA can be exposed by photographic film (the probes can also be made of 32P , which makes them radioactive in the same way), or florescent markers can be used so the targeted DNA can be highlighted under UV light. (note UV markers are also used in automated DNA sequencing)
probes can be used to -
To identify restriction fragments containing a particular gene out of the thousands of restriction fragments formed from a genomic library.
To identify the short DNA sequences used in DNA fingerprinting.
To identify genes from one species that are similar to those of another species. This has aided the identification of human genes.
To identify genetic defects. DNA probes have been prepared that match the sequences of many human genetic disease genes such as muscular dystrophy, and cystic fibrosis.
sequencing and copying DNA
the polymerase chain reaction - PCR
PCR is artificial DNA replication - its used to create multiple copy's of a genetic sample. this is also known as amplifying a sample.
this process is not identical to natural DNA replication in that it can only replicate short strands of DNA ( a few hundred bases long), the addition of primer molecules (short single strands of DNA 10-20 bases in length) is required to start the reaction and a cycle of heating and cooling is used to separate and bind strands rather than enzymes.
the first stage of PCR is the mixing of the genetic sample with extra DNA nucleotides and DNA polymerase enzyme
the mixture is then heated to 95 degrees centigrade to break the hydrogen bonds between complimentary base strands , making the samples single stranded
primers are then added to the mixture
the temperature is then lowered to 55 degrees allowing primers with complimentary bases to bond to the ends of the samples, DNA polymerase then also binds to these double stranded sections
the temperature is then raised to 72 degrees (the optimum temperature for DNA polymerase) the Polymerase then begins to bond complimentary free nucleotides to the strands, when the polymerase reaches the end of a strand a new double stranded DNA molecule is created.
the cycle can then be repeated to create additional copy's of the DNA sample
note: the binding of complimentary base pairs is known as annealing
translation - background info
this is the second stage of protein synthesis when the amino acids are assembled into a polypeptide based on the sequence of codons (three neucleotides that form a unit of genetic code in DNA or RNA) in the mRNA . this stage occurs in the ribosomes.
are assembled in the neucleolus from ribosomal RNA and protine . each ribosome conisits of two subunits and a groove into which mRNA can fit
is made in the neucleus and is passed into cytoplasm. they are capable of folding into hairpin shapes and have anticodons (three unpaired neucleotide bases) that can temporarily bind with a complimentry codon
translation - how it occurs
a molecule of mRNA binds to the ribosomes, two codons are attached to the small ribosomes subunit and are exposed to the large subunit , the first codon is always AUG. the mRNA fits in the groove between the two sub units , there's enough room for two codons (three nucleotides of the mRNA's chain) to be processed at a time.
the amino acids have to be activated , this is done by combining them with a specific molecule of tRNA , the tRNA had an anti codon a sequence of 3 nucleotides complimentary to a codon on the mRNA.
the mRNA slowly slides through the ribosomes, and as each codon enters the ribosomes its used to position the next amino acids by the temporary binding of the codon and anticodon aligning the amino acid in the correct position of the chain , its joined to the other amino acids by enzymes that cause condensation reactions to create peptide bonds between them
this guys a bit mad , but he explains it better that i do !
automated DNA sequencing is based on interrupt PCR and electrophoresis
DNA sequencing was initially done using radioactively labeled nucleotides. the development of automated gene sequencing has led to a rapid increase in the number of organisms that have been genetically sequenced in recent years.
as with PCR the reaction mixture the reaction mixture system contains DNA polymerase, primers and free nucleotides (some of which carry a florescent marker) , copy's of the template DNA replicated in PCR are also included. The florescent nucleotides are designed to throw of DNA polymerase from the strand to prevent the addition of any further nucleotides.
the primer joins to the end of the template strand, allowing the DNA polymerase to attach
the DNA polymerase attaches complimentary free nucleotides to the DNA strand
many new DNA strands are created and they all vary in size due to the adding of the florescent nucleotide at a random interval throwing off the DNA polymerase and stopping the construction of the complete strand , the new strands also all end in a different coloured florescent marker
the strands are then run through a machine (using a technique similar to electrophoresis) and a laser reads the colour sequences
this process is used by, and allowed for the human genome project
chromosome mutations - change in the structure of a chromosome , this could be deletion , inversion or translation
occurs in DNA replication and can be due to tar , UV light , X rays and Gamma Rays
DNA mutations - occur in DNA replication before cell division , Somatic mutations are not passed on but may contibute to aging or lead to cancers , mutation during meiosis and gamete formation can be passed on
Mutations - a random change in genetic material
point mutations - when one base pair replaces another , this can lead to
insertion/ deletion mutations
one or more nucleotide pairs are inserted or deleted , this kind of mutation always results in a frame shift
substitution - when one base pair is changed to a different base pair
deletion - when one or more base pairs are deleted from the sequence
addition - when one or more base pairs are added to the sequence
introduction to genetic engineering
reasons for genetic engineering -
improve a feature in the recipient organisms
inserting a gene into a crop plant to make it resistant to herbicides which will allow the farmers to use the herbicide to kill weeds
inserting a growth-controlling gene into livestock to promote muscle growth
engineers an organism to produce useful products
inserting human insulin into bacteria to produce quantity of the chemical for human use
inserting the gene for a pharmaceutical chemical into sheep so that the chemical is produced into milk and easily collected
inserting genes for beta carotene production into rice so that it can be converted into vitamin A when consumed
in genetic engineering the following steps have to be followed -
1) the gene has to be obtained
if the gene is being expressed in a cell then copies of mRNA can be taken and used as a template
the gene can be synthesized using a automated polynucleotide sequencer
A DNA probe can be used to locate the gene and then restriction enzymes can be used to cut it out
2)a copy of the gene is placed in a vector
placing it in a bacterial plasmid
insertion into a viral genome or yeast chromosomes
often vectors have to contain a regulatory piece of DNA
3) the vector carries the gene to the recipient cell
electroporation- a high voltage pulse used to interrupt the membrane
micro injection- the DNA is inserted into the host cells nucleus with a micropippette
viral transfer- uses the viruses mechanism to insert DNA directly
Ti plasmids can be inserted into soil bactirium and can then be used to infect plant and pass on the genes
liposomes - the dna can be rapped in lipid molecules which can cross the lipid membrane via diffusion
4) the recipient cell expresses the gene through protein synthesis
the following slides are a list of genetic diseases caused by mutations and how they occur
cystic fibrosis is an inherited genetic disease caused in 70% of cases by the deletion of one or several triplet base pairs in the CFTR gene, which is responsible for the production of channels for chloride ions into and out of cells, the ions are used to assist with water control in tissues , which also makes it responsible for the production of clear free flowing mucus. this deletion causes the channels to be thicker than usual and preventing them from regulating the flow of ions and water across the membrane. the result of this is the lungs, pancreas and many other organs producing a thick sticky mucus that blocks airways and other ducts causing the symptoms of cystic fibrosis.
sickle cell anemia
caused by an insertion mutation in the HBB gene, which is responsible for the production of beta-globins , a mutation in this gene means that the wrong sort of haemoglobin is produced , warping the structure of the red blood cell into a sickle shape, this causes the blood cells to carry less oxygen and die prematurely , this can result in anemia or dead blood cells blocking a blood vessel.
restriction enzymes and ligase enzymes
restriction enzymes are used to cut through DNA at specific points , these enzymes are extracted from Bacterial cells where they act as a defense system against viruses (they cut through the DNA the viruses insert as they insert it). a particular restriction enzyme will only cut an area of DNA (known as a restriction site) that complimentary to its active site (there are usually no more than 10 bases long). the enzymes catalyze a hydrolysis reaction to break the phosphate sugar backbone of the DNA leaving a staggered cut in the end of the DNA known as a sticky end.
Ligase enzymes are used in natural DNA replication to repair DNA strands, they catalyze a condensation reaction to join the sugar phosphate background. in order for ligase enzymes to join DNA cut using restriction enzymes , the samples must have initially been cut using the same type of restriction enzyme.
the LAC operation
Enzyme induction - this is when a bacterium starts producing proteins that it wasn't producing before in order to compensate for a change in environment
E-coli genraly respires glucose but can use lactose , if you grow e.coli with no lactose then add lactose to the culture medium , enzyme production can be triggered, the first enzyme is lactose permiase that transports the lactose into the cell
the second one is B- galactosade which catalises the hydrolosis of lactose into glucose and galactose.
The LAC operation
lac is short for lactose and the operon is a length of DNA consisting of structural genes (Lac Z codes for Beta Galactosidase , Lac Y codes for lactose permiase) and control sites.
when lactose is absent from the enviroment the first stage of the LAC operand is the regulatory gene being transcribed and translated to create a protein that binds to the operator region
however this protein covers part of the promoter region, preventing RNA polymerase from binding and mRNA being produced
When lactose becomes present in the environment ,some of it enters the cell and binds to a site on the repressor protein , causing it to change its shape so that it can no longer bind to the operator region and breaks away.
this exposes the operator bases and allows DNA polymerase to bind , allowing the transcription of genes Z and Y and the production of lactose permiase so that the bacterium can respire via the use of lactose
gene therapy is a technique used to treat some diseases and certain genetic disorders. the theory is that in the future doctors may be able to treat diseases by inserting a gene into a cell instead of using drugs or surgery. There are currently three methods that are being researched into how this could be accomplished , these include
- Replacing a mutated gene that causes disease with a healthy copy of the gene.
- Inactivating, or “knocking out,” a mutated gene that is functioning improperly.
- Introducing a new gene into the body to help fight a disease.
although the treatment appears promising, the method is still under intense study to minimize risks and research is only being carried out for diseases that have no other cure.
somatic cell gene therapy
as an organism grows, its cells become specialized to perform certain functions, within the cells some genes are specialized and others are not , though each cell will contain a complete genome, only some of the genes will be producing proteins.
augmentation is gene therapy by adding genes , some genetic conditions are caused by the inheritance of a faulty alleles , which leads to the loss of a gene product (polypeptide), engineering a working copy of the gene into the relevant specialized cells means that the polypeptide can be synthesized and the cell can start to function normally
the killing of specific cells can also be used as a therapy to help combat diseases such as cancers. gene therapy could be used to make cancerous cells express an allele that makes them vulnerable to certain chemicals or to attacks by the immune system
germline cell gene therapy
this is the genetic modification of a sperm, egg or zygote to ensure that a modified gene is entered into every cell in the body, meaning that the gene can code for a protein in every cell that it needs to.
some (transgenic) animals have been genetically engineered and occasionally the functioning allele has been passed on to there offspring.
genetic modification to counter a genetic disorder in a person may not stop the allele for the disorder being passed on to there offspring.
use of germline thrapy in humans is illigal due to the risk of creating a new disease or interfere with human evolution and as permanent modifications to the human genome raising a large number of ethical, moral and social issues
retroviruses are RNA containing viruses that use the enzyme reverse transcriptaise to copy there RNA into the DNA of a host cell. in effect "fooling the cell into copying it instead of its own DNA, making additional copies of the virus the only way to remove the virus is to kill the infected cell before they can replicate.
retroviruses can potentially be modified and used in genetic modification to insert a gene into a cell instead of the use of DNA extraction
meiosis - part one
• Homeobox genes control gell differentiation , they are known as master switches as they activate other genes to cause different growth patterns to occur
• Homeoboxes are a common system across all higher organisms (plants animals and fungi)
• They control growth plans (where things grow and when)
• There are 180 base pairs in a homeobox gene
• the gene’s contain transcription factors that activate other genes to cause other processes to occur
• below is another vidio from the dude from before, crash course evolutionary development and chicken teeth
• mutations in homeobox genes can cause body parts in the wrong place
• the genes are arranged in clusters called Hox clusters mutations of the clusters may have been the cause of more complex organisms
Homeobox (Homeotic Genes)
prophase 1 - chromosones coil and thicken (condense) homologus chromosomes pair to form bivalents , the chromatids break in each bivalent to form chismata , where sections of non sister chromatids are exchanged
metaphase 1-microtubiles attach to the centromere of each chromosome from the centrioles , the bivalents are moved to the equator of the cell
anaphase 1- chromosomes are seperated and pulled to opposite poles of the cell by the microtubiles
telophase 1 - neuclear envelope forms around each set ochromosomes to form two nuclei , the cell membrane pinches to form two cells (cytokinesis)
meiosis - part 2
prophase 2- nuclear membrane breaks up again, and centrioles replicate again and migrate to opposite poles of the cell
metaphase 2 - microtubiles attach between the centriols and the centromere of each chromosome . chromosomes align at the equator of the cells
anaphase 2- sister chromatids move to opposite poles
telophase 2 - the nuclear membrane reforms and cytokinesis occurs producing 4 haploid cells
meiosis and variation
sexual reproduction increases genetic variation by randomly combining genetic material from two organisms
meiosis increases genetic variation through :
crossing over, alleles switch from one chromosome to homologous chromosomes
genetic re assortment - during meiosis one parental and maternal chromosomes are randomly distributed between nuclear envelopes
random assortment - during meiosis two sister chromatids are randomly distributed between new cells
random mutations are also possible during interphase
sister chromatids wrap around each other forming a chiasmata , resulting in some chromatids breaking and joining to the opposing chromosomes , causing some genes to be swapped over , creating a new combination of alleles on the chromosomes
the homologus chromosomes line up in there bivalent during prophase 1 and separate randomly, resulting in new genetic combinations
sex linkage - genetic diagrams
why mainly males
females have two X chromosomes so are less likely to express the allies as they have another X chromosome, which if it lacks the mutation it will compensate for the faulty one as its dominant.
if a male is hetrozygous and its the allele for the faulty factor viii protein they will suffer from haemophilia A
in a genetic diagram always use the X and Y chromosomes for these as there actually based around the chromosomes not random genes!
when there are no dominant or recessive alleles , in this scenario both characteristics contribute towards the phenotype, f