Unit 1.4 Enzymes Flashcards
What is protease?
An enzyme that breaks down proteins
What does bile do?
It emulsifies fats and neutralises food leaving the stomach
What happens to carbohydrates?
They are broken down into simple sugars
What happens to protein?
It is broken down into amino acids
What can pH do at the wrong level?
Denature enzymes
What happens in the stomach and what type of pH is it?
The stomach has an acidic pH where proteases are released onto the food
What are fats broken down into?
Fats are broken down into fatty acids and glycerol
what is the purpose of amylase?
It’s an enzyme that breaks down Starch
What breaks down fats?
Lipase
What does the pancreas do?
Releases many enzymes including lipase, amylase and carbohydrates onto food entering the small intestine
What is an enzyme?
A biological catalyst that speeds up the reactions in the body
What are the two hypothesis of enzyme action?
Lock and key hypothesis and
Induced fit hypothesis
Explain the Lock and Key hypothesis
Only those substrates with a complementary shape to the active site will combine with the enzyme
Extremes of temperature and pH denature enzymes
I.e. shape of active site damaged
Enzyme-substrate complex cannot be properly formed
Explain the Induced Fit hypothesis
Supposed that the enzymes active site alters when substrate binds
Active site moulds round substrate
Active site is flexible and takes on the shape of the substrate
When products share released, the shape of the active site returns to normal
What are co-factors?
Name different types of co-factors
They are required for enzymes to work efficiently
There are three different types:
- Permanently bound to enzyme: prosthetic group (organic)
- not bound to enzyme: co-enzyme (organic)
- activators e.g. inorganic ions
Explain the chemical nature of enzymes
Enzymes are globular proteins
A majority are conjugated enzymes
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Protein part of enzyme (apoenzyme) + non-protein part (co-factor)
What is the ‘active site’?
The active site of an enzyme is where substrate molecules are held. Reactions occur here
What is ‘activation energy’?
The minimum amount of energy that a molecule needs for a reaction to occur
Enzymes are biological catalysts, why? How?
They increase the rate of biological reactions
How?
Mol A + Mol B (reversible reaction symbol) Mol C
Briefly describe an enzyme
Enzymes allow biochemical reactions to take place at their optimum rate at biological temperatures and pHs
How do enzymes work?
Enzymes are biological catalysts that speed up the rate of metabolic reactions without being used up themselves by lowering the activation energy.
What are the two types of reactions?
Catabolic reactions:
Where larger molecules are broken down into smaller molecules
A ——————> B + C
(Substrate). (Product)
Anabolic reactions:
Where smaller molecules are built up into larger, more complex molecules
X + Y ————-——> Z
(Substrate) (Product)
What is ‘metabolism’?
A set of chemical reactions that occur in living organisms in order to maintain life. In cells metabolic reactions take place quickly and thousands of reactions are taking place simultaneously. Order and control is essential if reactions are not to interfere with each other.
Describe a lysozyme
A lysozyme is a globular protein with a deep cleft across part of its surface. Six units of this substrate fit into the cleft.
…
Within a lysozyme, explain the roles of the protein
Enzyme - Lysozyme
Substrate - Polysaccharide
Active site - Cleft
H
H
H
What are the properties of enzymes?
Enzymes are specific
I.e. each enzyme will catalyse only one particular reaction
Enzymes are very effective and have a high turnover number. This means that they can convert many molecules of substrate per unit time
Chemical reactions need energy to start them off and this is called activation energy. This energy is needed to break the existing chemical bonds inside molecules. Enzymes lower the activation energy of the reaction that it catalyses. And so reduce the input of energy needed and allow reactions to take place at lower temperatures
What is an extra cellular enzyme?
An enzyme that is secreted by a cell and that works outside the cell. It is usually used for breaking up large molecules that would not be able to enter otherwise
What is an intracellular enzyme?
An enzyme that functions within the cell in which it was produced
What factors affect the rate of enzyme action?
Temperature
pH
Substrate concentration
Enzyme concentration
How is the configuration of the active site altered?
Environmental conditions, such as temp and pH, change the three dimensional structure of enzyme molecules. Bonds are broken
How does temperature affect enzyme activity?
How does pH affect enzyme activity?
How does substrate concentration affect enzyme activity?
How does enzyme concentration affect enzyme activity?
Define inhibitors
A substance that slows down or stops enzyme action
What are the different types of inhibitors?
Competitive and non-competitive
Describe a competitive inhibitor
This is where the inhibitor is a molecule which has a similar shape to the molecule, and therefor complementary to the active site. In case of enzymes, a competitive inhibitor may have the same shape as that of a substance, but doesn’t react in the same way. Rather than turning into the product, it simply uses up time and prevents substrates from getting to the active site
If the substrate concentration is increased so will the rate of reaction. Why?
The more substrate molecules the greater the chance of finding active sites leaving fewer to be temporarily occupied but the inhibitor.
By adding more substrate you can overcome the affects of the inhibitor by outcompeting it
What does a rate of reaction to substrate concentration graph look like with and without a competitive inhibitor?
Without the inhibitor will rise more steeply and quickly however it will level off. ‘With’ will take longer but will also reach the same point as ‘without’ and will level off too
What is an example of a competitive inhibitor?
Malonic acid (malonate) competes with succinate for the active site of succinic dehydrogenase an important enzyme in respiration
Describe a non-competitive inhibitor
The inhibitor becomes attached to the enzyme at a position other than the active site (the allosteric site), rendering the enzyme inactive. The attachment of the inhibitor to the enzyme alters the structure of the enzyme so that it becomes less active
The degree of inhibition cannot be reduced by increasing the number of substrate molecules.
Describe a graph…
What is an example of a non-competitive inhibitor?
Potassium cyanide attaches itself to part of the enzyme cytochrome oxidase and inhibits respiration
Explain the shape of the graph with no inhibitors
As the conc of substrate increases, the rate of reaction increases. There are more substrates to bond with the active site to form more enzyme-substrate complexes and more product. The rate of reaction will reach a constant because the enzymes have reached their maximum turnover rate. Therefore, enzymes are limiting the reaction. As you increase the substrate conc further, it no longer affects the rate of reaction because the enzymes active sites are working at their maximum turnover rate. Therefore, substrates are queuing up. Adding more substrate won’t do anything
Explain the shape of the graph with competitive inhibitors
A my power concentrations, the rate is lower because they are a similar shape to the substrate which is complementary to the active site but competes for the active site causing no product to be made when the inhibitor goes onto the active site. Adding more substrate, you can overcome the affect of the inhibitor by our competing it as the number of substrates is greater than the number of inhibitors
(Amount depends on amount of substrate)
Explain the shape of the graph with non-competitive inhibitors
The inhibitor is not complementary to the active site as it is not similar to the substrate. The inhibitor fits into the allosteric site and when this happens it changes the tertiary shape. The active site is no longer the same shape and cannot fit the substrates as it is not complementary
(Affect is solely due to inhibitor)
Discuss immobilised enzymes
Immobilised enzymes are enzyme molecules that are fixed, bound or trapped on an inert matrix such as a gel capsule (alginate beads).
These beads can be packed into glass columns. Substrate can be added to the top of the column and it reacts with the enzyme as it slowly flows down the column.
Once set up the column can be used again and again. As the enzyme is fixed it does not get mixed up with the products and is therefore cheaper to separate.
Immobilised enzymes are used widely in industrial processes, such as fermentation, as they can readily be recovered for reuse.
What are the principle methods for immobilising enzymes?
Adsorption - in glass or alginate beads. Enzyme is attached to the outside of an inert material
Covalent bonds - cross linkage to another chemical
E.g. cellulose or glyceraldehydes
Entrapment within a gel - (silica gel) the enzyme is held in a mesh or a capsule of an inert material
Encapsulation behind a selectively permeable membrane - membrane confinement
What is the method least likely to damage the enzyme?
Entrapment
The enzyme is entrapped within an inert matrix, such as alginate, silica or collagen, and cannot be washed out. The substrate and product molecules can diffuse in and out of the matrix, but this diffusion may limit the rate of the reaction. This is the most gentle method of entrapment, and does little damage to the enzymes.
Describe adsorption
The enzyme molecules are attached by weak physical forces to a support matrix, such as glass beads or carbon particles. This does not chemically modify the enzyme molecules, but the adsorption process may cause the enzymes to lose their shape and therefore their activity. The molecules may also become detached during the reaction
Describe enzyme immobilisation
Disadvantages of immobilised enzymes
Immobilisation may alter the shape of the enzyme
A slower rate of reaction as some of the enzyme active sites may not be available to substrate molecules
Enzymes are not free to move in solution so fewer collisions take place
(Collisions because of kinetic energy, discuss in answers where relevant)
Enzymes may detach
Expensive
Advantages of immobilisation
Product is not contaminated by the enzyme
The enzyme is easily removed and can be reused
Resistant to extreme conditions such as heat and pH - matrix protects enzymes with a protective barrier so it is more stable
Higher operating temperatures increase rate of reaction
The enzyme can be packed into columns and used over a long period
