Enzymes in Metabolism

Question 1

What is covalent modification?

Answer 1

When covalent bonds are made or broken.

Question 2

What is the effect of covalent modification?

Answer 2

This changes the enzymes shape so it is either made active or inactive. The concentration of active enzyme is changed, so the reaction rate is changed.

Question 3

How can a Kinase enzyme activate or inactivate an enzyme?

Answer 3

The covalent addition of a phosphate by a condensation reaction.

Question 4

What do phosphatase enzymes do?

Answer 4

Dephosphorlylate other enzymes causing them to be activated or deactivated.

Question 5

When blood sugar concentration falls which two liver enzymes are phosphorylated?

Answer 5

Glycogen synthase and glycogen phosphorylase

Question 6

What happens when kinase adds a phosphate group to glycogen phosphorlylase?

Answer 6

This activates the breakdown of glycogen to release more glucose.

Question 7

What happens when kinase phosphorylates glycogen synthase?

Answer 7

It is inactivated and stops synthesising glycogen.

Question 8

What is the name given to the inactive form of trypsin produced by the pancreas?

Answer 8

Tyrpsinogen

Question 9

Where is the trypsinogen enzyme cut?

Answer 9

Small intestine by proteases

Question 10

Give another example covalent modification?

Answer 10

When covalent bonds in the polypeptide chain are cut, so the shape of the enzyme changes

Question 11

What is the effect of a protease cutting the trypsinogen enzyme.

Answer 11

This converts the trypsinogen into the active form of enzyme trypsin.

Question 12

How can the rate of formation of products by a metabolic pathway be regulated?

Answer 12

By changing the affinity of the enzyme in the pathway for its substrate.

Question 13

What does the enzyme catalyse?

Answer 13

The rate-limiting step for the whole pathway

Question 14

What is the affinity changed by?

Answer 14

A modulator molecule that binds to the enzyme.

Question 15

What happens when a modulator binds?

Answer 15

It changes the shape of the enzyme, the active site and therefore the affinity for the substrate.

Question 16

What is the modulated enzyme called?

Answer 16

It is called an allosteric enzyme

Question 17

How does the modulator bind to the second binding site?

Answer 17

Through hydrogen and ionic bonds

Question 18

What is the name of the second binding site?

Answer 18

Allosteric site

Question 19

Why does the rate of reaction change?

Answer 19

The effectiveness of the enzyme

Question 20

Under which conditions will a positive modulator bind to the allosteric site

Answer 20

When a product of a metabolic pathway is in short supply.

Question 21

What is the effect of a positive modulator?

Answer 21

It increases the affinity of the enzyme for the substrate by binding to the allosteric site. This increases the rate of formation of all subsequent products in the pathway.

Question 22

When will a negative modulator bind to a different allosteric site of the enzyme?

Answer 22

When there is enough of the final product in the pathway.

Question 23

What is the effect of the negative modulator?

Answer 23

Reduces the affinity the enzyme has for the substrate.
Enzyme becomes less effective - Less substrate for next enzyme.
The whole pathway slows down.

Question 24

What is end product inhibition?

Answer 24

When the product of the final reaction accumulates and slows down the first enzyme of the pathway and so slows down its own synthesis.

Question 25

What two ways can the final product limit the effectiveness of the first enzyme of the pathway.

Answer 25

A competitive inhibitor or a negative modulator.

Question 26

What is the purpose of end product inhibition?

Answer 26

The cell does not waste energy synthesising more product.