L9 Catalytic Cofactors

Question 1

What is covalent catalysis?

Answer 1

Covalent catalysis is one of the four main strategies used by enzymes to catalyze specific reactions.

Question 2

How does covalent catalysis work?

Answer 2

Covalent catalysis involves the formation of a temporary covalent bond between a substrate molecule and a reaction group within the enzyme’s active site

Question 3

What types of metals can enzymes bind to, when catalysing reaction?

Answer 3

Enzyme often use bound metal ions in their reaction mechanisms

Metal can be tightly bound (metalloenzymes) E.g. transition metals: Fe2+/ Fe3+, Cu2+, Zn2+

Or loosely associated (metal activated) E.g. alkali and alkaline earth metal ions Na+, K+, Ca2+, Mg2+

Question 4

What are tightly bound and loosely associated metals called?

Answer 4

Tightly bound - metalloenzymes

Loosely associated metals - metal activated

Question 5

How do metal ions catalyse enzymes?

Answer 5

1) Lewis acid Catalysis
2) Stabilisation of transition states
3) Can increase binding interactions
4) Metal oxidation state changes can facilitate catalysis

Question 6

What are cofactors?

Answer 6

Certain enzymes require additional metal ions or small molecules to carry out their catalytic function

Question 7

What is a loosely bound/tightly bound coenzyme called?

Answer 7

Tightly bound coenzymes are called prosthetic groups

Loosely or dissociable type are called cosubstrates

Question 8

What is an apoenzyme?

Answer 8

An enzyme that is inactive on its own

Requires a cofactor to become fully active

Question 9

What is a holoenzyme?

Answer 9

Apoenzyme + cofactor = holoenzyme

Question 10

What is Adenosine monophosphate (AMP)?

Answer 10

It’s often found as a component or ‘building block’ in cofactors

Question 11

Why is NAD a major cofactor?

Answer 11

NAD exists in two forms: NAD+ (oxidisied) and NADH (reduced)

It’s ability to accept and donate electrons makes it a crucial player in many metabolic pathways