2.1.4 Enzymes - cofactors, coenzymes, prosthetic groups

Question 1

What is a cofactor?

Answer 1

A substance that helps to control the rate of enzyme reactions. Some cofactors are attached to the molecule, whilst others aren’t.

Question 2

How do you obtain cofactors?

Answer 2

They are inorganic and are obtained via the diet as minerals.

Question 3

What is a coenzyme?

Answer 3

Coenzymes are organic molecules that bind briefly to the active site before, or simultaneously with the substrate. Coenzymes may be changed when the enzyme reaction is done, so cannot be reused.

Question 4

How do you obtain coenzymes?

Answer 4

Many coenzymes are derived from vitamins since coenzymes are organic molecules.

Question 5

What is a prosthetic group?

Answer 5

A cofactor that is permanently bound to the enzyme molecule is known as a prosthetic group.

Question 6

What is a mineral ion cofactor?

Answer 6

A cofactor that temporarily binds to the enzyme molecule is known as a mineral ion cofactor.

Question 7

What is an example of a prosthetic group?

Answer 7

Zinc (Zn2+) is a prosthetic group for carbonic anhydrase.

Question 8

Explain how zinc works as a prosthetic group for carbonic anhydrase.

Answer 8

The products of aerobic respiration, carbon dioxide and water, move into the red blood cells and combine to form a weak acid called carbonic acid
CO2 + H2O –> H2CO3
This reaction is catalysed by carbonic anhydrase, which is an enzyme with a prosthetic group permanently bound
Zinc is permanently bound to carbonic anhydrase, which catalyses the interconversion of carbon dioxide and water to carbonic acid.
The carbonic acid dissociates to release hydrogen ions which remain in the cytoplasm, and hydrogen carbonate ions which diffuse out of the cells into the plasma.
H2CO3 –> H+ + HCO3-
Carbonic anhydrase is only able to catalyse the reaction between carbon dioxide and water to form carbonic acid when zinc ions are permanently bound. The carbonic acid can then dissociate into hydrogen carbonate ions, enabling carbon dioxide to be carried in the blood from the respiring tissues to the lungs for excretion.

Question 9

What is an example of a mineral ion cofactor?

Answer 9

Amylase can only digest starch to maltose if chloride ions are present.
(Cl- is a cofactor for amylase)