Question

Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Water soluble hormones acts on its target cell through second messenger system. Reasons (R) : The hormone receptor complex on the cell membrane activates G proteins thereby activating adenylate cyclase and catalyzing conversion of ATP to cAMP which activates protein kinases. In the light of the above statements, choose the most appropriate answer from the options given below :

• A. \( \text{Both (A) and (R) are correct and (R) is the correct explanation of (A)} \)
• B. \( \text{Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)} \)
• C. \( \text{(A) is correct but (R) is not correct} \)
• D. \( \text{(A) is not correct but (R) is correct} \)

Hint:

\textbf{Endocrinology: Hormone Action.} Remember the fundamental difference in the mechanisms of action between water-soluble and lipid-soluble hormones. Water-soluble hormones utilize cell surface receptors and second messenger systems, while lipid-soluble hormones typically bind to intracellular receptors and directly influence gene transcription. The cAMP pathway is a classic example of a second messenger system.

Answer 1

The Correct Option is A

Let's analyze the Assertion and the Reason: Assertion (A): Water soluble hormones acts on its target cell through second messenger system. Water-soluble hormones, such as peptide and protein hormones and catecholamines, cannot easily pass through the lipid bilayer of the cell membrane. Therefore, they typically bind to receptors located on the cell surface and trigger intracellular signaling pathways involving second messengers to exert their effects. Thus, Assertion (A) is correct. Reasons (R): The hormone receptor complex on the cell membrane activates G proteins thereby activating adenylate cyclase and catalyzing conversion of ATP to cAMP which activates protein kinases. This describes a common mechanism by which many water-soluble hormones exert their effects. The binding of the hormone to its cell surface receptor leads to the activation of G proteins. Activated G proteins can then stimulate adenylate cyclase, an enzyme that catalyzes the conversion of ATP to cyclic AMP (cAMP), a common second messenger. cAMP then activates protein kinases, which phosphorylate specific intracellular proteins, leading to the cellular response. Thus, Reason (R) is correct and accurately explains a major pathway through which water-soluble hormones act. Therefore, both the Assertion and the Reason are correct, and the Reason provides a valid explanation for the Assertion.