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AQA A2 Biology Unit 5
Transcript of AQA A2 Biology Unit 5
Image by Tom Mooring
AQA A2 Biology Unit 5
In terms of temperature regulation, there are two types of animal: Endotherms and Ectotherms. Endotherms have internal mechanisms that control and maintain their core body temperature, where Ectotherms rely on the environment to keep their bodies at a constant temperature.
Hormones are produced by glands that then secrete them into the blood, they are then carried throughout the blood stream until they reach their target cells, they are not taken there directly like with neurone messengers. It's kind of like a bus, you get to where you want to be eventually, but have to go around the entire route to get there first.
Response to Stimuli
Control of Heart Rate
Receptors work by detecting changes the body, different receptors are activated differently, like by heat, light, or mechanical pressure
of Protein Synthesis
One specific type of receptor is the Pacinian Corpuscle, it respond to mechanical pressure, so when a certain amount of pressure is put on the neurone in the middle, the gated ion channels open and an action potential is triggered.
Receptors contain neurones with gated ion channels in them, a gated ion channels will be opened when a variety of stimuli are detected, though each type of receptor is specific.
A taxes is the conscious movement of a motile organism whose direction determined by the direction of a stimulus, taxes can either be positive (towards the stimulus) or negative (away from the stimulus).
Some examples of taxes are light (phototropism), gravity (geotropism) and water (hydrotropism)
Kinesis is like a taxes, by the way that it is triggered by a stimulus however it is not directional or controlled, it is random, and is triggered by a negative stimulus.
An animal will detect the negative stimulus and start moving in random directions in order to increase the chances that it will end up in a more favourable environment, the more negative the stimulus, the faster the movement.
It's the reason woodlice go mental when you lift up the log theyre under.
Tropisms only occur in plants, and it is a growth movement that is used to get the plant into a more favourable position for growth. There are both positive and negative tropisms as it is a directional movement
More details about tropisms in the coordination section
Composed of the spine and brain.
All nerves that extend from the spine and around the body.
Autonomic nervous system:
Central Nervous System
Peripheral Nervous System
Voluntary Nervous System
Signals are sent to soft tissue, cardiac muscle and glands, it is involuntary
Conscious control of muscles
Excess exercise causes excess CO2 in the bloodstream
Chemoreceptors in the carotid arteries detect decrease in pH.
Send messages to the medulla oblongata
Sends messages via the sympathetic Pathway
Impulses sent to SAN which then causes the heart to speed up
Pressure receptors in carotid arteries detect blood pressure
Messages sent to medulla oblongata
Messages send via the Parasympathetic pathway
SAN receives impulses and heart rate slows down to reduce pressure
Messages sent via sympathetic pathway
SAN recieves impulses and heart rate increases to incrae pressure
TYPES OF CONTROL
Messages travel in blood plasma
Get to target cells that way and stimulate them
Longer lasting effect
Messages travel via neurones
Secrete neurotransmitters onto target cell
Direct contained effect
Chemicals secretes by certain types of mammalian cells, that effect the cells in their immediate vicinity
Stored in white blood cells and
when released causes the dilation of capillaries in the immediate vicinity, and increase their permeability, causing localised
Found in cell membranes, they are released upon injury and reduce the permeability of capillaries, blood pressure and neurotransmitters, and affect pain sensation
as a result
Plant Growth Factors
Plants have no nervous system, and still need to react to factors such as water, gravity and light in order to survive
They are produced all over the plant in many different types of cell
They affect growth. The speed, direction, specific areas that need to grow more than others
Act on tissues that release them.
IAA works by detecting where light is on a plant, then moving to where the plant is shaded, then causing the cells on the shaded side to elongate so that the plant falls into the light. It is made in the tip of a plant
Types of Muscle
Found in the intestines, places where the contraction of the muscle is autonomic
Found solely in the heart
Every muscle connected to the skeleton is a skeletal muscle and it is under conscious nervous control
Muscular Contraction- Sliding Filament
Structure of Skeletal Muscles
Calcium ion channels open
Calcium travels down t-tubules, and into sarcoplasmic reticulum
Bind to receptors on tropomyosin and moce it out the way
Myosin, with an unused ADP on it can now bind to Actin, it then releases its
Calcium stimulates ATPase to break down ATP into ADP
Energy then available to break actin and myosin bridge
This bit repeats as long as there is nervous stimulation
nervous stimulation stops.
Calcium ions actively transported out
Tropomyosin re-covers actin and myosin
Contraction ceases because actin and myosin can't bind
Neuromuscular junctions are similar to synapses in that they use acetylcholine to send the message across, when they bind to receptors on the post synaptic membrane, it causes it to become more permeable to Na+ and and so depolarises the membrane. so this allows for calcium ions to open, and then the contraction of the muscle is triggered.
The transmission of acetylcholine is halted by either acetyl choline diffusing out ofthe synaptic cleft or being broken dowby acetylcholineesterase which breaks it down into its substituents.
Bundles of fibres
Actin and Myosin
Structure of a Myofibril
Types of Muscle Fibre
Slower less powerful contractions
Big store of glycogen
Heavily populated with blood vessels
Loads of mitochondria
Faster, more powerful contractions
Thicker myosin filaments, also a lot more
anaerobic respiration, and so a lot of enzymes for that.
Lots of Phosphocreatine
Normal Blood Temperature
Heat Gain Centre
Heat Loss Centre
Expose Self to Sun
Cold receptors in skin
Heat receptors in skin
Flattening of hair
How does Vasoconstriction/Vasodilation work?
There are arteries that are connected by arterioles, to capillaries next to the skin, they are also connected by smaller 'connecting vessels' which are away from the skin surface.
During vasoconstriction, the arterioles constrict, forcing blood away from the surface of the skin and through the connecting vessels, which are dilated.
During vasodilation, the connecting vessel constricts, and the arterioles connected to the skin surface capillaries dilate, forcing blood towards the capillaries near the surface of the skin, so that heat is lost.
How do goosebumps do anything?
Goosebumps cause hairs on your arms to stand up, this creates a thin layer of still air trapped on the
surface of the skin, which it turns out is a very good insulator, so keeps cold out and heat in.
Ectotherms are reptiles, fish, and anything referred to as 'cold blooded'
Ectotherms have no internal mechanisms like endotherms do, so rely on the environment to provide their heat,
the ways they maximise the heat they gain
from the environment are:
Exposing themselves to the sun
Generating metabolic heat
It's important to regulate temperature, as enzymes can become denatured at high temperatures, or have significantly lower rate of operation at low temperatures, so to keep all of the body's process' running efficiently it is imperative temperature is regulated around an optimum temperature
Who Doesn't Love a Good Pancreas?
The Pancreas is a gland, it produces digestive enzymes and the hormones Glucagon and Insulin. They are pretty much made up of the cells that make that affore mentioned stuff, and the cells we are interested in are the ones that make the hormones.
They are called the Islets of Langerhans, and they can be divided into two groups:
Alpha Cells: That produce GlucAgon.
(They are the larger cell, and so produce the longer spelled
hormone, and A-lpha, Gluc-A-gon. Think A)
Beta Cells: That produce Insulin
Onset from childhood onwards
Because insulin can't be produced
Thought body may attack beta cells
Doesn't take long to develop
Controlled by insulin injections, taken 2-4 times a day, the correct amount of insulin is injected by monitoring biosensors.
Caused by glycoprotein receptors losing responsiveness to glucose. Or alternatively can be caused by a lack of insulin from the pancreas.
Develops slowly and is more common in obese people
Controlled by monitoring the amound of carb intake and matching this to exercise done.
Insulin injections, drugs that stimulate insulin production, or drugs that slow uptake of glucose can all be used to control the symptoms
The Second Messenger
Model of Blood Glucose Regulation (catchy)
Why Blood Glucose Varies
Consuming high sugar
foods can temporarily increase blood sugar levels as carbohydrates from food
are broken down
Production of glucose from glycerol and amino acids raises blood glucose levels
Breakdown of glycogen to glucose increases blood glucose levels
Adrenaline (first messenger) binds to cell surface membrane.
Activates Adenylate Cyclase
More enzymes activated
How do the cells work?
Beta cells detect an increase in blood glucose and so release
Insulin binds to receptors on a large variety of cells and causes
Change in glucose protein channel shape so more can enter
More carrier proteins
More enzymes that convert glucose to glucogen
Allows blood glucose levels to be lowered by
Muscles taking on more glucose in the form of glycogen
increased respiration to get rid of all the glucose
Increased convesion of glucose into fat.
Alpha cells detect a fall in blood glucose and so release glucoagon, liver cell receptors allow for the glucagon to bind to them and as a consequence:
An enzyme that converts glycogen to glucose is activated
Negative feedback is when the presence of something stops it being created or destroyed. Here the normal level of glucose stops the action of alpha and beta cells, that is the negative feedback.
Normal Blood Glucose Level
Blood glucose levels fall
Blood glucose levels rise
The rise in the BGL is what causes the action to stop, this is the negative feedback
More converstion of amino acids and glycerol to glucose
Detected by Alpha cells which produce glugagon
Detected by Beta cells which produce insulin
glucose by cells
Increased conversion of glucose to fat
Decrease in blood glucose level stops action, negative feedback
Single strand molecule, thymine is replaced with uracil.
Pentose sugar and phosphorous backbone
It is the same structure as the RNA over there
Made during DNA transcription, wherein a mirror image of the DNA is made during DNA replication. This then leaves the nucleus via the nuclear pores and enters the cytoplasm. Where it associates with ribosomes, and proteins are built.
Each triplet codon codes for an amino acid
Literally everyone loves amino acids.
TYPES OF FEEDBACK
Involve corrective measures within the body
When feedback causes a corrective measure to stop
corrective measure continues past normal levels and causes abnormal levels of a factor on the opposite side to the original disruption
Thermo regulation: Negative feedback when the corrective measures cause body temperature to normal, so corrective measures stop
Neurones: when restoring a neurone potential after an action potential, too much Sodium is pumped out so the neurone becomes mroe negative than the resting potential
Typhoid causes the degradation
of the thermo-regulatory system. It causes the body to continue 'warm-up' processes well past the normal body temperature, causing sufferers to die from Hyperthermia.
When the body gets very cold, it also causes the degradation of the thermo-regulatory system, causing the body to become even colder and eventually sufferer to die of Hypothermia
Stimulates the development of follicles in the ovaries.
Stimulates follicles to release oestrogen
Causes ovulation to occur
Stimulates ovaries to produce progesteom corpus luteum
One day I'll be a real baby!
*C'mon broken condom!*
Day 10 up over here
This pituitary gland is far too demanding
FSH + LH
The triplet anticodons on the Anticodon loop are complimentary to the mRNA sequence, and so are the same as the DNA triplet codons, except there it uracil where there is thymine
When mRNA is in the ribosome, tRNA comes floating over to bind with it and releases an amino acid into the chain of amino acids.
In this step, DNA is in copied and pre-mRNA is made. As we know from AS Level, DNA is composed of introns and exons, and introns are useless bits of DNA that don't actually code for anything. Pre mRNA is mRNA with all of these introns still in.
Hydrogen bonds between DNA are broken by DNA Helicase and the two strands are split
Need some Adenine and Cytosine now
This takes place in the nucleoplasm (cytoplasm of the nucleas), there are many free nucleotides in there, RNA polymerase then builds RNA from these free nucleotides, using the DNA strand as a template.
The process whereby introns are taken out of the DNA so that all that is left is the useful, coding DNA, if the introns were left in they would mess with the reading of the DNA, and incorrect proteins would be produced.
The resulting molecule is mRNA
The process whereby mRNA joins with a ribosome, as it binds with the starting codon AUG on the mRNA. Complimentary tRNA binds with the mRNA, which then releases an amino acid specific for that codon. This process happens again and an enzyme joins the two amino acids via a peptide bond.
tRNA molecules then bond along the mRNA, as the ribosome moves the molecule, two at a time, until up to 50 strong polypeptide is made.
tRNA molecules are re-released when they deposit their Amino Acid, they then leave to pick up another amino acid.
When the base substitution causes the codon to become a 'stop codon' these codons stop the polypeptide synthesis, if one of these is created the polypeptide synthesis will be stopped prematurely and the protein will not form properly and either not function properly or not function at all
When the substitution causes a different amino acid to be coded for, this has the potential to change the structure and shape of the protein, making it less functional or completely unfunctional, especially if it is an enzyme.
When the substituted base still codes for the same amino acid
Occurs when a nucleotide is lost from a sequence so that a frame shift occurs, where all of the nucleotides are moved up a position to replace the space of the other nucleotide. This can cause the entire dna chain to be completely unreadable and cause incorrect or no proteins to be made
Naturally they occur randomly but at a set frequency, with no external factors influencing it. However mutagenic agents include
High energy radiation that disrupt the DNA molecule
Chemicals that alter DNA structure or interfere with transcription.
Genetic Control of Cell Division
Stimulates the division of cells by a growth factor
binding to protein receptors on the cell surface membrane
and 'switching on' the genes necessary for cell replication.
Mutation can cause proto-oncogenes to become oncogenes, which can cause:
If the protein is always activated, the proto-oncogenes will stimulte cell division regardless of the prescence of a
The oncogene codes for growth factor which
stimulates cell division
Tumour Suppressor Genes
Inhibit the action of cell division, when they mutate, they are rendered inactive, and so no longer inhibit cell division, so it carries on and forms a tumor, which can be either benign or malignant
Totipotency and Cell Specialisation
Totipotent cells are cells that have the capability to turn into any type of specialised cell, in humans this is a fertlised egg, the first few cells of an embryo, and a few 'adult stem cells' specialised cells that can be converted. Most adult cells specialize irreversibly.
Regulation of Transcription & Translation
Genes aren't expressed by:
Breaking down the mRNA before it's read
Through some genes being expressed, and some not, cells become specialised
To trigger transcription, transcriptional factors must bind to the receptor molecule on the particular gene in order to initiate transcription, if a cell 'does not want' a gene to be expressed, there is an inhibitor blocking the transcriptional factor binding site, so transcription cannot be triggered.
All transcriptional factor receptors are inhibited until oestrogen comes in. Oestrogen binds to the receptor molecule, and changes the shape of the receptor site, so that it is no longer complimentary to the inhibitor, and is now complimentary to the transcriptional factor, it binds and mRNA is transcripted
siRNA allows for the breakdown of mRNA.
Double stranded RNA is cut into small pieces by an enzyme, these then bind with a differen enzyme, and travel over to the transcripted mRNA, the small bits of RNA then bind to the mRNA with it's complimentary bases, the enzyme then cuts into the mRNA so that it no longer codes for a polypeptide, is not translated, and the gene is not expressed.
Used to make DNA from RNA. Isolate a cell that has a plentiful supply of a gene that you want, the Reverse Transcriptase uses the mRNA present as a template to make cDNA, which is single stranded, DNA polymerase then makes this into a double stranded chain, then you have your cute little gene.
In Vivo Gene Cloning
Enzymes that cut up viral DNA, they cut DNA at a recognition sequence, leaves blunt ends or sticky ends. Cut 6 bases in to the sequence on either side, this is the palindromic sequence
Restriction Endonucleases cut into a plasmid at the
same recognition site as the gene they have just cut, this means that the available section of plasmid is complementary to the gene, so it is taken on by the plasmid by DNA helicase binding the complimentary base pairs.
The DNA is introduced into target cells, normally a bacteria. The bacteria and plasmid are mixed together in a medium containing calcium ions then warmed (to make the bacteria more permeable).
The plasmid used contains two genes for resistance: one that will be affected by the introduction of a new gene, and one that will not. It can be determine if a bacteria has taken on the plasmid if the bacteria becomes resistant to that antibiotic that is unaffected by the introduction of a new gene.
However, although it can be determined that the bacteria has taken on the plasmid, it cannot be determined if the plasmid has taken on the gene, for this,markers must be used.
Antibiotic Resistant markers: If a cell has taken on the gene, the 2nd gene for antibiotic resistance of another antibiotic, will be rendered inactive.
Flourescent Markers: Those that have taken on the required gene will flouresce
Enzyme Markers: Lactase, those that have taken on the gene will break down lactose
In Vitro Gene Cloning
1. DNA fragments, primers and DNA polymerase are put into a thermocycler, temp 95 degrees, this seperates the two strands.
2. The temperature is then reduced to 55 degrees to allow the annealing of primers, which provide a starting point for DNA polymerase to begin compiling a new DNA strand, the primer stops them joining together.
3. The temperature is then increased to 72 degrees, which is the optimum temperature for the DNA polymerase to start making new DNA chains from the template.
Doesn't require living cells
Use of Recombinant DNA Technology
Microorganisms & Animals
Genetically Modified to
Increase yield from animal or crop
Improve nutrients in product
Resistance to disease
Resistance to herbicides
Tolerance to environment
Antibiotics naturally produced by bacteria, GM improves quality and quantity
Insulin extracted from animals has human gene, so human insulin is produced, don't need to kill animal and insulin is not rejected
GM bacteria make enzymes used in industry
Herbicide resistant exam
Pest resistant crops
Gene Therapy of Cystic Fibrosis
The result of a deletion of AAA base triplet, meaning an amino acid is missing in a protein, the normal CFTR so it cannot transport chloride ions across the membrane, so water also does not leave, so mucus builds up in the lungs, causing breathing difficulties, mucus build up, greater susceptibily to infection.
Gene Replacement the defective gene is replaced with a healthy gene
Gene Supplementation, copies of the healthy gene are added alongside the unhealthy gene, the healthy gene is dominant and so will be accepted.
Germ Line: replacing a defective gene in a fertilised egg with a healthy gene, meaning all cells will develop healthily.
Somatic cell gene therapy targets only the cells that are only affected.
Delivery of the Gene
Using a Harmless Virus
The cold virus is a good little vector because it injects it's DNA into host lung cells, scientists take advantage of this by making it harmless by altering it's replication ability, and then giving it a plasmid containing the gene that codes for the correct protein.
In vivo gene cloning of the healthy CFTR gene, the bacteria are then left to reproduce to there are many copies of the plasmid, this is then sprayed into the nostrils of sufferers.
Locating and Sequencing Genes
So say you have a super massive strand of DNA, and you wanna find where in particular a gene is on that massive ass strand, well, this is where DNA probes come in. DNA probes are complimentary to the base sequence of the gene you're after- once it binds, you'll be able to see where it is by either the Radioactivity, or the Fluorescence it emits
Gel electrophoresis is when a variety of nucleotides
are put in 4 test tubes, each with DNA polymerase, primers, and complimentary DNA, and terminator nucleotides. In the tube strands of complimentary DNA are being made, and the terminator nucleotides, each different tube gets a different terminator nucleotide, A, T, C, or G are added randomly so eventually you end up with a test tube of A, AG, AGA,AGAT, AGATC etc etc. They are placed at the top of an electrified gel plates, and the lighter, and therefore shortest ones travel down first, then the next biggest one goes down but because there's already a mark there, it just adds another mark further up, where the previous shorter strand didn't have one, thus
showing the DNA sequence.
Order of nucleotides for mutated genes known, DNA probe complimentary to the mutated gene section created, PCR done to create many copies of the probe, if the probe is taken up, the radioactive probe will show on an X-ray film, if not, the probe will not show, and it can be shown that the person does not have the mutated gene.
Used by prospective parents who want to find out if they have the capability of producing affected offspring, or used to detect the early stages of cancer, by detecting mutated proto oncogenes, or tumour suppressor genes.
Relies on the vast number of introns people have, which contain 'core sequences' which are just repetitions of the same codons, which repetitions, and how many there are, determine the unique DNA. The combinations of these repeated bases means that no two individuals have exactly the same genome, BUT the more similar this genome is, the more closely related a person is to another. I.e. in paternity tests.
Gel Electrophoresis can only sort 500 bases at a time, however genes are normally a lot bigger than this, as a result, DNA must be cut into fragments and put in, this means they get jumbled up, and restriction mapping allows people to determine the order they were originally in.
Look at gel thing, and see what nucleases created what fragments, and how big they were. Then look at the combined one, and place them on the plasmid, doing the most choppy one first
An action potential is triggered by Sodium
gated ion channels opening, this causes an influx of sodium ions, which then triggers more channels to open, steadily, the action potential travels up the neurone, until it reaches the end of the knob, and the local circuit is depolarised, causing the diffusion of acetyl choline across the synapse, this binds to receptoprs on the post synaptic knob, this triggers an influx of calcium ions, which depolarises the local circuit, causing Sodium ion channels in that
neurone to open, and the process to
Node Of Ranvier
The depolarisation causes the membrane potential to become more positive, once it reaches +40mV, this causes the Na+ channels to close, and K+ channels to open, so K+ is pumped out, in an attempt to make the membrane more negative again, positive feedback then occurs as the membrane is made too negative :'( so then K+ is pumped back in then the resting potential is restored.
Transmission of an Action Potential
Acetyl Choline is the neurotransmitter, it is held in vesicles in the presynaptic knob, when an action potential reaches it, the vesicles diffuse towards the synapse, diffuse across it to an area of low concentration and bind to receptors on the post synaptic knob.
ACh released in small amounts by one to reach threshold value
Multiple release ACh to reach threshold value