Final answer:
A second messenger in a G-protein signal transduction cascade is a molecule like cyclic adenosine monophosphate (cAMP), which relays signals inside the cell. An effector protein like adenylate cyclase produces cAMP in response to an external signal. These second messengers initiate various intracellular activities by activating enzymes such as Protein Kinase A (PKA).
Step-by-step explanation:
Second Messengers and Effector Proteins in G-Protein Signal Transduction
In a G-protein signal transduction cascade, a second messenger is a molecule that helps relay signals from a receptor on the cell surface to the inside of the cell, resulting in a physiological change. A classic example of a second messenger is cyclic adenosine monophosphate (cAMP).
When a signal molecule binds to a receptor on the cell surface, it activates a G-protein, which then activates an effector protein. Adenylate cyclase, an example of an effector protein, is responsible for converting ATP to cAMP in response to a signal.
cAMP acts as a second messenger that leads to the activation of Protein Kinase A (PKA), which in turn, may regulate other proteins through phosphorylation, trigger metabolic changes, modify ion channels, or impact gene expression and protein synthesis. Similar mechanisms are involved with another second messenger, inositol triphosphate (IP3), which alongside diacylglycerol (DAG), is produced by the action of the effector enzyme phospholipase C.