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Biology 12 Unit 4
Transcript of Biology 12 Unit 4
How do Enzymes Work?
• molecules are so small and the reaction so fast, we’ve never clearly seen how enzymes work
• 2 models used to explain how enzymes work:
1. Lock and Key Theory
• E and S meet during the reaction, and
fit together perfectly
from the very beginning, like a lock and key
Τhe liver is a critically important organ in
digestion & homeostasis.
Part 1 Enzymes
METABOLISM AND METABOLIC PATHWAYS
sum of all the chemical reactions occurring in a cell
A series of reactions that proceed in an orderly, step by step manner
One reaction leads to the next
Each step within the metabolic pathway requires a
5. The Presence of INHIBITORS
o Inhibitors: molecules that bind to the enzyme in some way to
prevent or reduce the rate
of substrate binding to enzyme
o Several ways in which inhibition can work:
a) Competitive Inhibition
• a molecule that looks like the substrate can compete for space at the
(the place where the substrate binds to enzyme)
slows down the reaction rate - the inhibitor binding to E can be
REVERSIBLE or IRREVERSIBLE.
• Obviously, the more inhibitors are added, the lower the rate of reaction and
is going to be made.
Biology 12 Unit 4
Hormonal Control of Digestive Gland Secretion
: substances that are produced by one set of cells and affect a different set of cells
transported in blood
pancreas also has an endocrine function: produces the hormones
INSULIN and GLUCAGON
Main Classes of Nutrients
4) Vitamins & Minerals
Small Intestine: The Food Processor
• Up to this point, only some digestion has taken place (
starch in the mouth and protein in the stomach
). Most of
digestion and absorption
of most nutrients occur in the small intestine.
• Divided into three zones: the
DUODENUM, JEJUNUM, and ILIUM
Reasons why metabolic pathways exist:
• It is not possible in biological systems to have a single reaction that could produce complex molecules from simple reactants.
(e.g. 6CO2 + 6H2O ⇒ C6H12O6 + 6O2 would never happen in a cell in one step)
• One pathway can lead to several others, intermediate products of one pathway can be
• When you have more than one step, it means that there are more places where the overall reaction can be
ENZYMES: Biological Catalysts
: a protein that can speed up a chemical reaction without being consumed.
What are Enzymes made of?
1) A protein part called an
that gives it its specificity (i.e. exactly what reaction it will catalyze)
2) A non-protein group called a
• Enzymes are the sites of chemical reactions,
but aren’t used up in the reaction or permanently changed by the reaction
(hold reactant molecules together long enough for them to react)
: the reactant(s) in an enzyme’s reaction
• the equation for an enzyme-catalyzed reaction is always:
E + S ES E + P
: the place where the substrates actually bind on the enzyme.
2. Induced Fit Theory
• we now believe that the enzyme actually
slightly when it binds the substrates(get a better tighter grip)
• after reaction takes place, the ES complex separates, and the enzyme re-assumes its original shape (
now free to catalyze another reaction
How does an Enzyme Work?
required for the reaction to proceed
• Activation Energy: the energy that must be supplied to cause molecules to
react with one another.
Enzymes do this by bringing the substrate molecules together and
holding them long enough
for the reaction to take place.
FACTORS AFFECTING ENZYME ACTIVITY
• enzymes are proteins, so are affected by the same sorts of things that affect proteins
• since the shape of enzymes determines
the shape of the active site anything
that changes the shape of an enzyme will affect the enzymes function
• some factors are:
: most human enzymes prefer pH’s of 6 - 8 (some exceptions: pepsin in the stomach - pH ~ 2, trypsin in the small intestine - pH ~ 8)
o If the pH is too low or too high compared to the optimum pH, the enzyme
(a denatured protein is one that has lost its
, and therefore its ability to form an
o if the temperature is below the optimum temperature of 37 C, the rate of reaction will be
o the lower the temp. drops, the lower the
rate of reaction
o very low temps don’t normally denature the enzyme
3. Concentrations of SUBSTRATES
o If the concentration (abbr. = “[ ]”) of substrate increases, amount of
o The rate of product formation will usually increase too
o However, after a certain [ ], the rate won’t increase anymore, as all the enzymes are “
” with substrates and can’t work
o if the [ ] of substrate decreases, the rate of product formation will generally
decrease as well
4. Concentration of ENZYMES
o Limits the overall rate of reaction
o Providing there is adequate substrate (and there are typically millions more substrate molecules than enzyme molecules), the more enzyme you add,
the more product you get
, and the less enzyme you have, the
b) NON-COMPETITIVE INHIBITION
• inhibitor binds to
on enzyme (not the active site)
• inhibitor may look
from the substrate
• when the inhibitor binds, it causes the enzyme to change shape at the active site so S cannot bind.
• binding may be
reversible or non-reversible
Examples of Inhibition
o Reversible inhibition is often used as a normal way of slowing down metabolic pathways (e.g. an intermediate or final product may be a reversible inhibitor of another enzyme in the pathway).
o Inhibitors can also be chemicals introduced into a system from the
, and can act as
medicines or poisons
. e.g. penicillin is a medicine that kills bacteria. It works by binding irreversibly to the enzyme that makes bacterial cell walls.
ATP - The Molecule of Energy
o Cells use Adenosine Triphosphate when they require energy. ATP is used for all reactions requiring energy, like
synthesis, muscle contraction, active transport
o ATP is a nucleotide composed of the base adenine and the sugar ribose, plus three phosphate groups. ATP has two high-energy P bonds (phosphate bonds). When they break,
energy is released
• ATP breaks down to ADP (adenosine diphosphate) and inorganic phosphate (P or “Pi”) when it releases energy.
• If energy is added to the system, the reverse action will occur.
ATP ADP + P + Energy
ADP + P + Energy ATP
• ATP, ADP and Pi are not destroyed during energy transfers. They are constantly being
formed and broken down.
THE DIGESTIVE SYSTEM
The process of breaking down ingested food, both mechanically and chemically
, into molecules small enough to move through epithelial cells and into the internal environment of the body.
: The passage of digested nutrients from the small intestine into the
blood or lymph
, which then distributes them through the body.
: the expulsion of indigestible residues from the body.
• During digestion, proteins are broken down into amino acids, carbohydrates into glucose, fats to glycerol and fatty acids, and nucleic acids to nucleotides.
• Your mouth is where digestion (both chemical and mechanical) begins.
• The mouth receives food, chews it up (
), moistens it, and starts to digest any starch (
) in the food.
• The mouth is divided into an anterior
(contains several bones) and a posterior
, which is composed of muscle tissue. That thing that hangs down in the back of your throat people think is their tonsils is really the
, and is the end part of
. (Tonsils lie on the sides of the throat).
• A normal adult mouth has
. The purpose of teeth is to chew food into pieces that can be swallowed easily.
• There are three sets of
that produce SALIVA:
(under lower jaw).
• Saliva contains the enzyme
which allows starch digestion to begin in the mouth, even before the food is swallowed.
• Once food has been chewed, it is called a
• Food is then passed through the back of the mouth when you swallow. The first region that it enters is called the
SOFT PALATE MOVES BACK
to cover openings to nose (nasopharyngeal openings).
(WINDPIPE) MOVES UP under a flap of tissue called the
, blocking its opening. When food goes down the "wrong way" it goes into the trachea, and is then
coughed back up
• The food then has one route to go: down the
• Esophagus: a long muscular tube that extends from
pharynx to stomach
. Made of several types of tissue.
• Food moves down the esophagus through
(rhythmical contractions of the esophageal muscles).
• Food bolus reaches the end of the esophagus, passing through the
, and entering the stomach.
o It is a thick-walled, J-shaped organ that lies
on left side of the body beneath the diaphragm.
o It can stretch to hold about half a gallon (~2 liters) of solids and/or liquids in an average adult.
o It consists of three layers of
that contract to churn and mix its contents
o The mucus lining of the stomach contains inner
. Gastric juice contains
PEPSINOGEN and HCl
(hydrochloric acid). When the two combine, pepsinogen forms
PEPSIN, a HYDROLYTIC ENZYME
that breaks down proteins into smaller chains of amino acids called peptides.
o HCl gives stomach a pH of ~3. Highly corrosive. This
kills bacteria in food and helps break it down
o Why doesn’t the stomach digest itself? This is because its inner wall is protected by a thick layer of
secreted by mucosal cells.
o After 2-6 hours (depending on the type of food), the food has been turned into a semi-liquid food mass called
, and the stomach empties into the first part of the small intestine (called the duodenum). This emptying is controlled by the
at the bottom of the stomach.
• It is about 7 meters long (~23 feet), compared to 1.5 m (5 feet) for large intestine.
• The first 25 cm of small intestine is called the DUODENUM. The duodenum plays a major role in digestion. It is here that
SECRETIONS SENT FROM THE LIVER AND PANCREAS
to break down fat , carbs and protein are received.
• The liver produces
, an emulsifier not an enzyme, which is sent to the duodenum via a duct from the GALL BLADDER (where bile is stored).
• Bile is a thick green liquid (it gets its green colour from
byproducts of hemoglobin breakdown
(another function of the liver).
• Bile contains emulsifying agents called
BILE SALTS which break FAT into FAT DROPLETS
sends pancreatic juice into duodenum through the same duct as the bile travels through.
• The juice contains enzymes and sodium bicarbonate (NaHCO3)
• NaHCO3 makes the juice
(pH ~ 8.5). It neutralizes the acid chyme and make the small intestine
• Pancreatic juice contains hydrolytic enzymes including pancreatic amylase (digests
starch to maltose
), trypsin (digests
protein to peptides
), and lipase (digests
fat droplets to glycerol & fatty acids
• The LIVER, GALL BLADDER, AND PANCREAS are required for digestion but
NEVER see food
The walls of the duodenum and small intestine are lined with millions of GLANDS that produce juices containing enzymes that finish the digestion of
protein and starch
Secretions from the intestinal glands contain digestive enzymes:
o Consists of
COLON and RECTUM
(the rectum is thelast 20 cm of the colon). Opening of rectum is called
o Τhe colon has 3 parts(
ascending, transverse, and descending
MAIN FUNCTIONS OF LARGE INTESTINE
REABSORPTION OF WATER
from indigestible food matter (feces)
Absorption of certain vitamins
Feces also contain bile pigments, heavy metals, and billions of E. coli. While there is no question that they are parasites, they provide a valuable service for us. These bacteria break down some indigestible food and in the process produce some
vitamins that are in turn absorbed by the colon.
Comprehensive Summary of DIGESTIVE ENZYMES
o The breakdown of food (fats, carbohydrates, proteins) into molecules small enough to be absorbed requires the action of specific enzymes.
o Each enzyme has specific site where it works, and a specific pH range in which it can operate.
o All are hydrolytic enzymes that catalyze a reaction of the substrate with water.
The small intestine is specialized for both digestion and absorption.
Receives enzymes from
pancreas and intestinal glands
bile from the liver
8.5 due to bicarbonate ions
released from pancreatic juice
Hormones control digestion
(CKK, gastrin, secretion)
Large surface area (
folding, villi, microvilli
Villi have capillary network giving a large blood supply because it is connected to
hepatic portal vein
Villi contains lacteals which are part of the
Small Intestine walls are
o ABSORPTION: takes place across the wall of each villus (can happen
passively or actively
o Nutrient can now enter the blood or the lymphatic system (depending what it is)
o Fatty acids & glycerol are absorbed across the villi, & recombined into fat molecules in the epithelial cells of the villus
fats then move into the
of each villus and enter the
fats will eventually enter the blood stream at the
o Glucose & amino acids enter the blood through the capillary network.
o The blood vessel from the villi in the small intestine merges to form the
HEPATIC PORTAL VEIN
which leads to the liver.
1) Keeps blood concentrations of nutrients, hormones etc. constant (e.g. converts
glucose to glycogen
glycogen to glucose between meals
to keep blood glucose levels constant).
Interconversions of nutrients
(e.g. carbohydrates to fats, amino acids to carbohydrates and fats).
3) Removes toxins from the blood (
). Removal of unwanted particulate matter from the blood through the
mediation of macrophages
Production of Bile
. Up to 1.5 liters of bile per day!
5) Destroys old
red blood cells
Production of urea
. (deamination of amino acids and excretion of resulting ammonia as urea, uric acid, etc.)
Manufacture of plasma proteins
such as fibrinogen and albumin.
8) Manufacture of cholesterol.
9)Storage of iron.
10) Storage of vitamins.
: is released from pancreas when
glucose levels are high
(released directly into blood and travels to target cells throughout body)
tells liver to “
store glucose as glycogen
” (ie. glucose in blood is taken up by cells)
lowers blood [glucose]
: opposite to insulin
is released from pancreas when glucose levels are low
tells liver to “
release glucose from glycogen
raises blood glucose levels
People who don’t produce insulin or enough insulin, or who lack insulin receptors on target cells, will suffer from diabetes.
HORMONES control secretion of specific digestive juices
Primary source of energy
o Diet should consist primarily of
(not refined sugars)
o Carbohydrates are digested eventually to glucose, which is stored by liver as
Glucose is only fuel brain will use
Most fats can be made by liver.
o Fats in food are mostly found in animal products (meat and dairy). These are especially high in saturated fats (saturated fats tend to be solid at room temp).
o High fat and protein diets are number one cause of death in North America (heart disease, strokes, hypertension, many forms of cancer, many other disorders and diseases).
o You should get ~15% of your calories from fat. Most Americans and Canadians get between 40 and 60% of their calories from fat!
o Fats are high in calories (> twice as many per gram (9.1) as carbohydrates or protein (4.4.))
o Protein is necessary for tissues, metabolism, enzymes etc.
It is NOT an energy food
o Of the twenty types of amino acids, 8 cannot be manufactured by humans --
- called essential amino acids.
o Protein deficiency is the most common form of malnutrition in poorer
countries. The swollen abdomen of starving children is caused by edema due to the lack of plasma proteins in the blood.
o Most North Americans eat more than 2 to 3 times the amount of protein they
4. Vitamins & Minerals
• Vitamins are organic compounds that the body can't produce but must be present in the diet (though they are only required in very small amounts). Lack of any one vitamin can cause serious health disorders.
• Vitamin D: deficiency leads to rickets(bowing of legs). Manufactured naturally by skin upon exposure to sun.
o Vitamin C:
deficiency leads to scurvy
o Riboflavin: deficiency causes fissures of lips (cheilosis)
o Niacin: deficiency causes dermatitis of areas of skin exposed to light (called pellagra)
o Many vitamins are
. e.g. Niacin: coenzyme of NAD. Riboflavin: coenzyme of FAD.
o Best source of vitamins is
fresh fruits and vegetables
in a balanced diet.
are also needed by the body.
: gram amounts needed daily. Na, Mg, P, Cl, Ca.
• e.g. Calcium makes up structural component of important tissues (e.g. bone, cartilage), and is also a necessary ion for the transmission of nerve impulses across synapses and the initiation of muscle contraction.
: (“trace elements”). Minute amounts (micrograms) needed. Very specific. e.g. Fe (for hemoglobin), Iodine(for the hormone thyroxin).
refers to the breaking down of molecules. The term
refers to the building up of molecules, or
Metabolism is the sum of catabolism and anabolism.
are spontaneous and release energy, while
require an input of energy in order to occur.
ATP is a carrier of
energy between exergonic and endergonic reactions.
• Enzymes are Highly Specific
each enzyme speeds up only
enzyme names usually end with the suffix “ase” (or sometimes “sin” e.g. trypsin, pepsin)
o increasing the temp towards the optimum will
the rate of reaction and product formation (as it speeds up the rate at which substrates bump into enzymes)
o however, temps above the optimum will
slow the rate of reaction
and a temp that is too high (above about 45 °C) will
o HCN (hydrogen cyanide) is a lethal irreversible inhibitor of enzyme action in human.
o Lead (Pb++) and other
(like mercury (Hg++) and cadmium) are non-competitive inhibitors that bind irreversibly to enzymes and make them denature.
METABOLIC RATE AND THE THYROID AND PARATHYROID GLANDS
o The thyroid gland is a large gland
located in the back of the neck.
One of the products of the thyroid gland is that it produces a
hormone called calcitonin.
Calcium is a crucial molecule that serves various purposes in our bodies such as,
nerve conduction, muscle contraction, and blood clotting.
When the calcium levels in our blood rise,
the thyroid gland secretes calcitonin to allow calcium to be deposited into our bones
, until the calcium levels even out.
o These four small glands are located
behind the thyroid gland.
When our body does not have an adequate supply of calcium in the blood stream, the
parathyroid gland releases the Parathyroid hormone, (PTH).
This hormone promotes the release of calcium from the
kidney’s and the intestinal tract.
Once the blood calcium levels are back to normal,
PTH is no longer secreted.
, which is simply the region between mouth and esophagus where swallowing takes place.
• Swallowing is a
(requires no conscious thought).
• To prevent food from going down your air passages, some clever manoeuvring is necessary.
peptides to amino acids
and maltase digests maltose (a disaccharide)
. Other enzymes made here digest other
the sugar in milk).
is an open sore in the wall of the stomach caused by a gradual disintegration of the tissue.
typically there is a thick layer of mucus that protects the wall of the stomach.
when this layer is compromised due to a bacterial infection or overuse of the inflammatory response, an ulcer is formed and if left untreated it can become a perforated ulcer which can be life threatening.
Most cases of diarrhea are acute, meaning they are sudden due to a bacterial or viral infection in the small intestine or the large intestine. Most commonly known as food poisoning.
Severe diarrhea can lead to dehydration, as well as disturb the hearts contraction due to an imbalance of salts in the blood.
Some people are afflicted with chronic diarrhea.
Persistent inflammation of the intestine that results in recurrent bouts of cramping and bloody diarrhea is known as Crohn's disease.
Researcher's believe that it's caused by a misdirected immune response, in severe cases small, or large parts of the colon must be removed.