4.4- Cofactors, Coenzymes, Prosthetic Groups

Question 1

What are cofactors and coenzymes?

Answer 1

Cofactors are non-protein components necessary for the effective functioning of an enzyme
These are called coenzymes when it is an organic molecule. Derived from vitamins

Vitamin K is a cofactor which controls blood clotting after injury.

Question 2

Where are inorganic cofactors obtained from?

Answer 2

obtained via the diet as minerals (iron, calcium, chloride and zinc ions).

Example: enzyme amylase, which catalyses the breakdown of starch contains a CL- ion that is necessary for the formation of a correctly shaped active site.

Question 3

What are prosthetic groups with example?

Answer 3

Cofactors. They are required by certain enzymes to carry out their catalytic function.
They are tightly bound to the enzyme protein and form a permanent feature of the protein.
Example: zinc ions (Zn2+) form an important part of the structure of carbonic anhydrase, an enzyme necessary for the metabolism of carbon dioxide.

Question 4

What are inactive precursor enzymes?

Answer 4

Enzymes that are produced in inactive form, especially if they cause damage within the cells producing them or to the tissues. Or if their action needs to be controlled and only activated under certain conditions.
-usually need to undergo a change in tertiary structure in order to be activated and this can be done by the addition of a cofactor.
- precursor enzyme before cofactor added= apoenzyme
After (activated) = haloenzyme

Question 5

What other factors can activate precursor enzymes? With example

Answer 5

• action of another enzyme.
• change in conditions (pH / temp). These precursor enzymes are called zymogens or proenzymes.

Eg. When inactive pepsinogen is released into the stomach to digest proteins. The acid pH brings about the transformation into the active enzyme pepsin. This protects the body tissues against the digestive action of pepsin.