2.3 Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts

Question 2

What is the now rejected hypothesis for how enzymes work?

Answer 2

the lock and key hypothesis

Question 3

What is the recently accepted hypothesis for the mechanism of enzyme action?

Answer 3

The induced fit model

Question 4

What are intracellular enzymes and name an example?

Answer 4

enzymes that act within cells e.g. catalase

Question 5

What are extracellular enzymes and name an example?

Answer 5

enzymes that are released from cells to break down large nutrients outside the cell e.g. amylase and trypsin

Question 6

What are the 2 enzymes involved in the digestion of starch?

Answer 6

• amylase

- maltase

Question 7

What enzyme is involved in the digestion of proteins?

Answer 7

trypsin

Question 8

What are the factors that affect enzyme activity?

Answer 8

• temperature
• pH
• substrate concentration
• enzyme concentration

Question 9

What is the temperature coefficient (Q10)?

Answer 9

a measure of how much the rate of reaction increases with a 10 degrees C rise in temperature

Question 10

Why do enzymes denature at high temperatures?

Answer 10

the bonds holding the protein together vibrate more which causes the bonds to strain and break which changes the shape of the tertiary structure and the active site is no longer complementary to the substrate

Question 11

What is the optimum temperature?

Answer 11

the temperature at which the enzyme has the highest rate of activity

Question 12

Why does a change in pH denature enzymes?

Answer 12

A change in [H+] alters the active site, causing the enzyme to denature

Question 13

What is renaturation?

Answer 13

If the pH does not change too drastically from the optimum and then returns to the optimum the protein can resume its normal shape

Question 14

How does [substrate] affect the rate of an enzyme controlled reaction?

Answer 14

when [substrate] is increased the number of substrate molecules, atoms or ions in a particular volume increases which leads to a higher collision rate with the active site and thus formation of more enzyme-substrate complexes

Question 15

How does [enzyme] affect the rate of an enzyme controlled reaction?

Answer 15

The number of available active sites increases leading to the formation of more enzyme-substrate complexes

Question 16

What is competitive inhibition?

Answer 16

a molecule/part of a molecule has a similar shape to the substrate and can bind to the active site, preventing the substrate from doing so

Question 17

Name 2 examples of competitive inhibitors

Answer 17

• statins

- aspirin

Question 18

What is non-competitive inhibition?

Answer 18

The inhibitor binds at an allosteric site which changes the shape of the enzyme so the substrate can no longer bind.

Question 19

Name 2 examples of non-competitive inhibitors

Answer 19

• organophosphates used as insecticides

- Proton pump inhibitors

Question 20

What is end-product inhibition?

Answer 20

enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the product of a reaction e.g. ATP

Question 21

What is the difference between cofactors and coenzymes?

Answer 21

Cofactors are a non-protein component that help enzymes carry out their function. Coenzymes are cofactors that are organic molecules.

Question 22

What is the difference between a prosthetic group and a cofactor?

Answer 22

Prosthetic groups are tightly bound and form a permanent feature of the protein.

Question 23

What is precursor activation?

Answer 23

A cofactor is added to an apoenzyme which activates it forming a holoenzyme

Question 24

What does precursor activation do?

Answer 24

Changes the tertiary structure of the enzyme

Question 25

What is an example of precursor activation?

Answer 25

when inactive pepsinogen the pH transforms it into active pepsin