Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Intracellular receptors that act as transcription factors become activated by physiological ligands. Reason (R): They are activated in the interior of the cell (unlike extracellular receptors) because their physiological ligands are lipophilic in nature. In the light of the above statements, choose the most appropriate answer from the options given below:

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

Hint:

Lipophilic molecules (like steroids) pass through cell membranes like ghosts. They go straight inside to find their intracellular receptors.

Answer 1

The Correct Option is A

Step 1: Concept Intracellular receptors reside in the cytoplasm or nucleus of target cells. Unlike surface receptors, they directly bind lipid-soluble molecules that can pass straight through the plasma membrane.

Step 2: Meaning Lipophilic means fat-loving or hydrophobic, allowing a molecule to dissolve through the lipid bilayer of a cell membrane without needing a transporter protein.

Step 3: Analysis * Assertion (A) is correct: Intracellular receptors (like steroid, thyroid, or retinoid receptors) function as ligand-activated transcription factors. Once they bind their ligand, they interact with DNA to alter gene expression. * Reason (R) is correct: These receptors are located inside the cell because their signaling ligands (such as steroid hormones) are highly lipophilic. This lipid solubility allows them to diffuse straight across the plasma membrane to reach the interior of the cell. * Explanation assessment: The reason explains why these receptors are located and activated inside the cell rather than on the surface, directly supporting the assertion.

Step 4: Conclusion Both statements are true, and (R) provides the correct explanation for (A). Final Answer: (A)