Enzyme Catalysis

Question 1

Describe enzyme catalysis

Answer 1

The rate of reaction increases by using an enzyme as a biological catalyst

Question 2

Describe what is meant by acid-base catalysis

Answer 2

Acceleration of a chemical reaction by the addition of an acid or a base, which is not consumed in the reaction

Question 3

What is specific base catalysis?

Answer 3

When hydroxide is the attacking species

Question 4

What is specific acid base catalysis?

Answer 4

When H3O+ is the attacking species

Question 5

Acid-catalysed reaction has more/less steps than base-catalysed including proton transfers

Answer 5

more

Question 6

Acid catalysis always begins with a positive/negative charge

Answer 6

positive

Question 7

What is the action of oxioreductases?

Answer 7

Transfer of electrons

Question 8

What is the action of transferases?

Answer 8

Group transfer reactions

Question 9

What is the action of hydrolases?

Answer 9

hydrolysis

Question 10

What is the action of lyases?

Answer 10

Addition of groups to double bonds
OR
Formation of double bonds by removing groups

Question 11

What is the action of isomerases?

Answer 11

Transfer of groups within molecules to yield isomeric forms

Question 12

What is the action of ligases?

Answer 12

Formation of bonds by condensation reactions coupled to ATP cleavage

Question 13

Enzymes have strongest affinity for the ________ state of the reaction they catalyse

Answer 13

transition

Question 14

What enzyme family does chymotrypsin belong to?

Answer 14

Serine protease enzymes

Question 15

Chymotrypsin uses a ______ residue to enhance the nucleophilic ability of serine

Answer 15

histidine

Question 16

Active sites contain residues that can participate in H+ transfer. List 3 things that may happen to the active site:

Answer 16

• activate nucleophiles required in catalysis
• stabilise charged groups
• Increase electric interactions that may stabilise transition state

Question 17

Enzymes catalyse reactions by binding with the substrate and transition state. This interaction releases _____, which stabilises the transition state, ______ the activation energy

Answer 17

energy

lowers

Question 18

What 2 things must enzymes have to increase the number of successful collisions to form E-S complexes?

Answer 18

• close proximity

- correct orientation

Question 19

An enzyme can be best describes as performing catalysis by:
A lowering the enthalpy of the reaction transition state
B lowering the entropy of the reaction transition state
C lowering the free energy of the reaction transition state
D lowering the internal energy of the reaction transition state
E lowering the heat of the reaction transition state

Answer 19

C lowering the free energy of the reaction transition state

Question 20

The side-chain of which of the following amino acids is able to act as a nucleophile in an enzyme catalysed reaction?
	A	Alanine
	B	Glycine
	C	Isoleucine
	D	Serine
	E	Valine

Answer 20

D Serine

Question 21

The side-chain of which of the following amino acids would best be able to mediate proton transfer steps in an enzyme catalysed reaction?
	A	Alanine
	B	Glutamine
	C	Histidine
	D	Leucine
	E	Tryptophan

Answer 21

C Histidine