Question

1. The catabolic Activation Protein (CAP) is a regulatory protein associated with several carbohydrate metabolism operons in bacteria.

a) Describe the activation / inactivation of CAP and how it affects the transcription of downstream genes. Include any important co-factors required for CAP where it binds DNA, and under what circumstance is it active / inactive. Do not discuss the downstream genes, refer to them as 'active' or 'inactive'.

b) What is the relationship of the enzyme adenyl cyclase to the CAP system? Include in your discussion the influence of glucose concentration on its activity.

c) What is the advantage of having CAP system in addition to the primary control of carbohydrate metabolism by operons?

Answer 1

a) Describe the activation/inactivation of CAP and how it affects the transcription of downstream genes. Include any important co-factors required for CAP where it binds DNA, and under what circumstance is it active/inactive. Do not discuss the downstream genes, refer to them as 'active' or 'inactive'.

Catabolite activator protein (CAP) is activated by cyclic AMP which is an important cofactor require for CAP binding to DNA. Because of its activation by cAMP, it is also called cyclic AMP receptor protein (CRP). It is inactivated in the absence of cAMP.

how it affects the transcription of downstream genes?- refer to figure attached

b) What is the relationship of the enzyme adenyl cyclase to the CAP system? Include in your discussion the influence of glucose concentration on its activity.

the cAMP is a second messenger which is released as glucose levels drop. In the absence of glucose, the enzyme adenyl cyclase is activated. It acts on ATP molecules, removes its two phosphates, and results in the formation of cyclic AMP. cAMP activates CAP which in turn stimulates synthesis of the enzymes that break down non-glucose food molecules.

Cyclic AMP binding with CAP changes the conformation of the protein slightly, making it binding to DNA easy. CAP dimer binds to a specific DNA sequence, that is present upstream of the RNA Polymerase binding promoter region.

c) What is the advantage of having a CAP system in addition to the primary control of carbohydrate metabolism by operons?

The advantage of having a CAP system in addition to the primary control of carbohydrate metabolism by operons is to utilize another source of energy when glucose is rare.

In the presence of plenty of glucose bacteria ignores other energy source but in its absence, it utilizes cAMP- CAP machinery to utilize an alternate source of energy.