Which of the following is a second messenger signal?
to. CAMP
b. IP3
DAG
d. G protein-coupled receptor and
A, B, and C only
The correct answer and explanation is :
Correct Answer: A, B, and C only
Explanation (300 words):
Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. These second messengers help propagate and amplify the signal inside the cell to produce a physiological response.
A. cAMP (cyclic adenosine monophosphate) is a classic second messenger. It is synthesized from ATP by the enzyme adenylyl cyclase, which is activated by certain G proteins. Once produced, cAMP activates protein kinase A (PKA), which then phosphorylates specific target proteins to regulate processes such as metabolism, gene expression, and ion channel conductivity.
B. IP3 (inositol 1,4,5-trisphosphate) is another well-known second messenger. It is produced when the enzyme phospholipase C (PLC) cleaves a membrane phospholipid called PIP2 into IP3 and DAG. IP3 travels to the endoplasmic reticulum (ER), where it binds to calcium channels, triggering the release of calcium ions into the cytoplasm. Calcium itself can act as a third-level messenger in some systems.
C. DAG (diacylglycerol) is generated alongside IP3 in the PLC signaling pathway. While IP3 is water-soluble and diffuses through the cytosol, DAG remains in the membrane and activates protein kinase C (PKC), which phosphorylates a variety of proteins to mediate responses like cell growth or differentiation.
D. G protein-coupled receptor (GPCR) is not a second messenger; it is a receptor located on the cell membrane that interacts with extracellular ligands (like hormones or neurotransmitters) and activates intracellular G proteins. These G proteins then trigger the production of second messengers like cAMP, IP3, or DAG.
Therefore, the correct answer is “A, B, and C only” because cAMP, IP3, and DAG are all true second messengers, while GPCR is the receptor that initiates the signaling cascade.