Unit 1.4 Enzymes

Question 1

What is protease?

Answer 1

An enzyme that breaks down proteins

Question 2

What does bile do?

Answer 2

It emulsifies fats and neutralises food leaving the stomach

Question 3

What happens to carbohydrates?

Answer 3

They are broken down into simple sugars

Question 4

What happens to protein?

Answer 4

It is broken down into amino acids

Question 5

What can pH do at the wrong level?

Answer 5

Denature enzymes

Question 6

What happens in the stomach and what type of pH is it?

Answer 6

The stomach has an acidic pH where proteases are released onto the food

Question 7

What are fats broken down into?

Answer 7

Fats are broken down into fatty acids and glycerol

Question 8

what is the purpose of amylase?

Answer 8

It’s an enzyme that breaks down Starch

Question 9

What breaks down fats?

Answer 9

Lipase

Question 10

What does the pancreas do?

Answer 10

Releases many enzymes including lipase, amylase and carbohydrates onto food entering the small intestine

Question 11

What is an enzyme?

Answer 11

A biological catalyst that speeds up the reactions in the body

Question 12

What are the two hypothesis of enzyme action?

Answer 12

Lock and key hypothesis and
Induced fit hypothesis

Question 13

Explain the Lock and Key hypothesis

Answer 13

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

Question 14

Explain the Induced Fit hypothesis

Answer 14

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

Question 15

What are co-factors?
Name different types of co-factors

Answer 15

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

Question 16

Explain the chemical nature of enzymes

Answer 16

Enzymes are globular proteins

A majority are conjugated enzymes
|
Protein part of enzyme (apoenzyme) + non-protein part (co-factor)

Question 17

What is the ‘active site’?

Answer 17

The active site of an enzyme is where substrate molecules are held. Reactions occur here

Question 18

What is ‘activation energy’?

Answer 18

The minimum amount of energy that a molecule needs for a reaction to occur

Question 19

Enzymes are biological catalysts, why? How?

Answer 19

They increase the rate of biological reactions

How?
Mol A + Mol B (reversible reaction symbol) Mol C

Question 20

Briefly describe an enzyme

Answer 20

Enzymes allow biochemical reactions to take place at their optimum rate at biological temperatures and pHs

Question 21

How do enzymes work?

Answer 21

Enzymes are biological catalysts that speed up the rate of metabolic reactions without being used up themselves by lowering the activation energy.

Question 22

What are the two types of reactions?

Answer 22

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)

Question 23

What is ‘metabolism’?

Answer 23

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.

Question 24

Describe a lysozyme

Answer 24

A lysozyme is a globular protein with a deep cleft across part of its surface. Six units of this substrate fit into the cleft.
…

Question 25

Within a lysozyme, explain the roles of the protein

Answer 25

Enzyme - Lysozyme
Substrate - Polysaccharide
Active site - Cleft

Question 26

H

Question 27

H

Question 28

H

Question 29

What are the properties of enzymes?

Answer 29

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

Question 30

What is an extra cellular enzyme?

Answer 30

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

Question 31

What is an intracellular enzyme?

Answer 31

An enzyme that functions within the cell in which it was produced

Question 32

What factors affect the rate of enzyme action?

Answer 32

Temperature
pH
Substrate concentration
Enzyme concentration

Question 33

How is the configuration of the active site altered?

Answer 33

Environmental conditions, such as temp and pH, change the three dimensional structure of enzyme molecules. Bonds are broken

Question 34

How does temperature affect enzyme activity?

Question 35

How does pH affect enzyme activity?

Question 36

How does substrate concentration affect enzyme activity?

Question 37

How does enzyme concentration affect enzyme activity?

Question 38

Define inhibitors

Answer 38

A substance that slows down or stops enzyme action

Question 39

What are the different types of inhibitors?

Answer 39

Competitive and non-competitive

Question 40

Describe a competitive inhibitor

Answer 40

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

Question 41

If the substrate concentration is increased so will the rate of reaction. Why?

Answer 41

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

Question 42

What does a rate of reaction to substrate concentration graph look like with and without a competitive inhibitor?

Answer 42

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

Question 43

What is an example of a competitive inhibitor?

Answer 43

Malonic acid (malonate) competes with succinate for the active site of succinic dehydrogenase an important enzyme in respiration

Question 44

Describe a non-competitive inhibitor

Answer 44

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.

Question 45

Describe a graph…

Question 46

What is an example of a non-competitive inhibitor?

Answer 46

Potassium cyanide attaches itself to part of the enzyme cytochrome oxidase and inhibits respiration

Question 47

Explain the shape of the graph with no inhibitors

Answer 47

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

Question 48

Explain the shape of the graph with competitive inhibitors

Answer 48

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)

Question 49

Explain the shape of the graph with non-competitive inhibitors

Answer 49

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)

Question 50

Discuss immobilised enzymes

Answer 50

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.

Question 51

What are the principle methods for immobilising enzymes?

Answer 51

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

Question 52

What is the method least likely to damage the enzyme?

Answer 52

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.

Question 53

Describe adsorption

Answer 53

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

Question 54

Describe enzyme immobilisation

Question 55

Disadvantages of immobilised enzymes

Answer 55

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

Question 56

Advantages of immobilisation

Answer 56

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