Question

Questions on cAMP Pathway. Short answers

1. What role does cAMP play in cell signaling?

2. Why is the regulation of the cAMP dependent pathway important?

3. What are two molecules that inhibit the cAMP dependent pathway?

4. What role does cAMP play in cell signaling?

5, Cyclic AMP is synthesized from ATP by what?

6. In what way is cAMP cyclical? What does the molecule do that has earned it this name?

Answer 1

1. cAMP is cyclic Adenine monophosphate. It acts as a second messenger. Normally in a signalling pathways , a signal activates nearby effector molecules which release secondary messenger which activates or inhibits some proteins.

cAMP is a second messenger in G protein coupled receptor pathway. When the ligand binds to GPCR the G protein is activated. ( G protein is a trimeric protein which has 3 subunits alpha, beta and gamma) The activated G protein activates adenylyl cyclase to form cyclic AMP formation from ATP. This cAMP in turn activates protein kinase A which phosphorylates many proteins.

2. cAMP activates protein kinase A which causes phosphorylation of many proteins like enzyme converting glycogen to glucose, many transcription factors, enzyme involved in heart muscle contraction. But all these process like glycogenolysis, heart muscle contraction or certain transcription factors has to be activated only at certain conditions not always so they have to be regulated. There are different mechanism to regulate it like intrinsic GTPase activity of G alpha or inhibitory G protein.

3. Inhibitory G protein (G _i) which inhibits adenylyl cyclase so reduce cAMP and cAMP phosphodiesterase which converts cyclic AMP to AMP by breaking phosphodiester bond. Both these molecules reduce cAMP levels.

5. Adenylyl cyclase

6. Cyclic AMP is derived from AMP . AMP has a ribose sugar, a phosphate group attached to 5th carbon of ribose sugar and adenosine. In cyclic AMP the phosphorus becomes cyclic i.e phosphorus is joined between 3 and 5 carbon of ribose sugar thereby giving a ring like or cyclic structure therefore it is called cyclic AMP or more specifically 3'-5' cyclic AMP.