Enzymes

Question 1

Why is a substrate broke down by an enzyme?

Answer 1

For hydrolysis reactions, entry of substrate to active site introduces a strain/pressure into the molecule which makes it easier for bonds to be broken and so lowers the activation energy.

Question 2

Define Activation Energy

Answer 2

The minimum amount of energy required for a reaction to take place.

Question 3

What is the order in which enzymes work in order to form the enzyme and product?

Answer 3

Enzyme + substrate -> Enzyme substrate complex -> enzyme product complex -> enzyme + product

Question 4

What is catabolism?

Answer 4

Breakdown reactions.

Question 5

What is anabolism?

Answer 5

Build up reactions.

Question 6

What is a cofactor?

Answer 6

Some enzymes do not work effectively unless a non protein cofactor is attached.

Question 7

What are some example of an enzyme and cofactor?

Answer 7

Succinate dehydrogenase - a respiratory enzyme. FAD. Hydrogen is removed from succinate and picked up by FAD (to form FADH2).
Chloride ions act as cofactors for salivary amylase.

Question 8

What an enzyme inhibitor?

Answer 8

Molecules that bind to enzymes that decrease their activities.

Question 9

What are the two types of enzyme inhibitor?

Answer 9

Competitive and non competitive.

Question 10

What is a competitive inhibitor?

Answer 10

It closely resembles the structure of the substrate and so competes for the active site, but doesn’t remain there permanently.

Question 11

What is a non competitive inhibitor?

Answer 11

It doesn’t resemble the substrate and may act in different ways:
They bind to a part of the enzyme away from the active site, altering the overall shape of the enzyme molecule, including the active site. The inhibitor may leave the enzyme so that the active site regains its active site.
Inhibitors bind to the enzyme molecule, leaving the enzyme permanently damaged or the enzyme could be reversed to normal.

Question 12

What are the advantages of enzyme immobilisation?

Answer 12

Production can take place continuously.
The product is enzyme free, so purification costs are reduced.
The enzyme can easily be reused.
Since the enzyme is supported, it’s stability improves. This means that it can be active over a great number of pH ranges and temperatures.

Question 13

What is covalent bonding in terms of enzyme immobilisation?

Answer 13

Covalent bonding onto a solid support e.g. cellulose fibres.

Question 14

What are the advantages and disadvantages of covalent bonding?

Answer 14

Enzyme not washed away. Resistant to pH and temperature changes. Most widely used.
Relatively expensive. Some active sites may be blocked by support material or adversely altered in structure.

Question 15

What is encapsulation in terms of immobilising enzymes?

Answer 15

Encapsulation in a partially permeable membrane. E.g. Nylon.

Question 16

What are the advantages and disadvantages of encapsulation?

Answer 16

Enzymes not bound, so active sites are not blocked and activity is not adversely affected. Enzymes cannot leak out.
Substrate has to diffuse through mesh. Some enzymes may leak out through mesh.

Question 17

Name 3 enzyme inhibitors as therapeutic drugs.

Answer 17

Penicillin
Alpha1 antitrypsin (A1AT)
Aspirin.

Question 18

What does penicillin effect and how?

Answer 18

It helps defend a bacterial infection.
It targets peptidoglycan transpeptidase which is the formation of cross links in bacterial walls.
They walls loose their strength causing the bacteria to burst.

Question 19

What does A1AT effect and how?

Answer 19

Damage effect of elastase during respiratory infection.
Elastase produced by white blood cells in respiratory tract.
Prevents loss of elasticity in the lungs and reduction of lung infection.

Question 20

What does aspirin effect and how?

Answer 20

Minor pain caused by damaged tissue releasing prostaglandin.

Relief of symptoms such as minor pain and inflammation.

Question 21

What is an enzyme?

Answer 21

Biological catalysts.
Speed up metabolic reactions.
The enzymes themselves are not changed by the reaction and can be reused.
Enzymes are globular proteins.

Question 22

Explain the specificity of enzymes.

Answer 22

This is because the enzymes active site has a precise shape and distinctive chemical properties so that only a specific type of substrate molecule can bind.

Question 23

What is the induced fit model for enzyme action?

Answer 23

It proposes that instead of being an exact fit, the enzyme active sites match very very closely to the shape of the substrate. It proposes that the active site could mould itself around the substrate, forming a precise fit.

Question 24

What is a prosthetic group?

Answer 24

Prosthetic groups are another type of cofactor. For example haem. (not in student guide)

Question 25

What is a coenzyme?

Answer 25

Non protein, organic molecules necessary for enzyme action. They are not permanently attached, unlike other cofactors.

Question 26

Explain the trend in a graph for enzyme activity of increasing substrate concentration.

Answer 26

At low substrate concentration an increase in concentration increases enzyme activity-it is a limiting factor. This is because a greater concentration of substrate molecules increases the chances of collision with enzyme molecules. Therefore, more enzyme substrate complexes are formed. At high substrate concentrations an increase in conc. does not cause a further increase in activity. This is because at high substrate concentrations the enzymes are fully employed and so, at any one moment, all the active sites are occupied.

Question 27

Explain the trend in a graph for enzyme activity for increasing enzyme concentration.

Answer 27

An increase in enzyme concentration increase the rate of reaction. At high enzyme concentration, activity may level off, but only if there is insufficient substrate. This is because an increase in the concentration of enzyme molecules increases the chance of successful collisions with substrate molecules. (There is normally only an incline phase since enzymes are used over and over and so function efficiently at very low concentration.)

Question 28

Explain the trend in a graph for enzyme activity for increasing pH.

Answer 28

Changes from the optimum pH cause a decrease in enzyme activity. This is because the nature of the protein, and so, the active site of the enzyme are altered by changes in pH. In particular ionic bonds in the tertiary structure are disrupted. pH is a measure of hydrogen ions (H+) concentration and, as the concentration of hydrogen ions changes, the charges of the R groups of amino acids are altered: at low pH a high concentration of H+ causes negatively charged R groups to lose their charge : at high pH a low conc. of H+ causes positively charged R-groups to lose their charge. So at non optimal pH the substrate attaches less readily to the enzyme and their is a specific pH at which the charges in the active site best facilitate the formation of an enzyme-substrate complex.

Question 29

Explain the trend in a graph for enzyme activity for increasing temperature.

Answer 29

At low temperatures an increase in temperature causes an exponential increase in enzyme activity-typically, a 10°C rise in temperature doubles the rate of enzyme activity. This is because an increase in temperature provides more kinetic energy for the collision of enzyme and substrate, so the rate of formation of enzyme-substrate complexes increases. At high temperatures (typically above 40°C) an increase in temperature forces a sharp decline in enzyme activity. This is because the bonds holding the tertiary structure of the enzyme molecules are broken down and so the active sites loses its complementary shape for substrate attachment-the enzyme is denatured.

Question 30

What are all the different types of immobilising enzymes?

Answer 30

Adsorption
Covalent bonding
Cross-linking
Encapsulation
Entrapment

Question 31

What is an example of an enzyme with optimum temperature of 90°C?

Answer 31

Enzymes from thermophilic bacteria that live in hot springs are active at temperatures up to 90°C.

Question 32

What provides increased thermostability in enzymes that act in hotter temperatures?

Answer 32

The large number of disulphide bonds that provides increased thermostability.