Consider this pathway: signaling ligand �¨ G protein-coupled receptor �¨ G protein �¨ adenylyl cyclase �¨ cAMP.
Identify the second messenger.
Answer:
A)G protein
B)GTP
C)adenylyl cyclase
D)cAMP
The second messenger in this pathway is D) cAMP (cyclic adenosine monophosphate).
To identify the second messenger, it is important to understand the sequence of events in the signaling pathway. Here's how you can find the answer step-by-step:
1. The pathway starts with a signaling ligand (also called a ligand or extracellular signaling molecule).
2. The signaling ligand binds to a G protein-coupled receptor (GPCR), a type of transmembrane protein located on the cell surface.
3. The activated GPCR then interacts with a G protein, causing a conformational change in the G protein.
4. The G protein, in its activated form (when bound to GTP), dissociates from the receptor and can now interact with various downstream effectors, including adenylyl cyclase.
5. Adenylyl cyclase is an enzyme activated by the G protein. When activated, adenylyl cyclase converts ATP (adenosine triphosphate) into cAMP.
6. Finally, cAMP acts as the second messenger by binding to and activating various protein kinases, leading to downstream cellular responses.
Therefore, in this pathway, the second messenger is cAMP (answer D).