Enzymes

Question 1

What is the active site of an enzyme?

Answer 1

The active site is a small section of the three-dimensional protein molecule which is specific to the substrate the enzyme acts on.

Question 2

What is the name given to the model of enzymes and substrates fitting together?

Answer 2

The lock and key model.

Question 3

How do enzymes catalyse reactions?

Answer 3

Enzymes catalyse reactions by lowering the activation energy required for a reaction to take place.

Question 4

There are three catalytic strategies - name them.

Answer 4

Covalent catalysis, acid-base catalysis and metal ion catalysis.

Question 5

How does covalent catalysis work?

Answer 5

By breaking and reforming active bonds.

Question 6

What does acid-base catalysis require the presence of?

Answer 6

Proton donors or acceptors.

Question 7

What does metal ion catalysis need?

Answer 7

A metal ion cofactor.

Question 8

There are hundreds of enzymes, which can be classified according to…?

Answer 8

The reaction they catalyse.

Question 9

Name some of the types of enzymes, as classified by the reactions they catalyse.

Answer 9

Oxxidoreductases, transferases, hydrolases, lyases, isomerases, ligases/synthases.

Question 10

Many enzymes require …………., of which NAD(P) is an example.

Answer 10

Cofactors.

Question 11

NAD(P) is a cofactor used by several oxidoreductases. What does it do?

Answer 11

It acts as an electron carrier.

Question 12

Many cofactors are derived from…?

Answer 12

Vitamins.

Question 13

Name two factors which can affect enzyme activity.

Answer 13

pH and temperature.

Question 14

Why does a change in pH affect enzyme activity?

Answer 14

A change in pH changes the charge on amino acids, which is important for enzyme function.

Question 15

How does temperature affect enzyme activity?

Answer 15

Temperature increases chemical reactions, but eventually the enzyme will be denatured and stop working.

Question 16

Name the two types of enzyme inhibition.

Answer 16

Competitive and non-competitive.

Question 17

Outline how competitive enzyme inhibition works.

Answer 17

The inhibitor mimics the structure of the substrate and competes for binding at the active site. The enzyme is therefore non-functional as the substrate cannot bind.

Question 18

Can competitive enzyme inhibition be turned on and off?

Answer 18

No.

Question 19

Outline non-competitive enzyme inhibition.

Answer 19

The inhibitor binds to the substrate and changes the binding site, preventing the enzyme from binding easily, although it might still be able to bind.

Question 20

Can non-competitive enzyme inhibition be turned on and off?

Answer 20

Yes it can, to regulate enzymatic pathways.

Question 21

Penicillin is a short peptide which is used as an antibiotic to kill bacteria - how does it work?

Answer 21

Penicillin inhibits glycopeptide transpeptidase, which cross-links bacterial cell walls. The cell walls are therefore not built properly, so the bacteria cells die.

Question 22

Why does penicillin only kill bacteria cells?

Answer 22

Penicillin works on cell walls. Only bacteria have cell walls so it doesn’t affect other cells.

Question 23

Give a common example of covalent modification.

Answer 23

Phosphorylation.

Question 24

Which enzyme catalyses phosphorylation?

Answer 24

Kinase.

Question 25

True or false? When ATP phosphorylates an enzyme, the enzyme can be activated OR deactivated?

Answer 25

True.