Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): The myelin sheath consist primarily of lipid
Reason (R): The relative proportion of protein and lipid varies with the type of membrane and it's role.
Choose the correct answer from the options given below:

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

Hint:

Contrast these two extreme membrane compositions:
- Myelin membrane (Electrical insulation) \(\rightarrow \approx 80\%\) Lipid, \(20\%\) Protein.
- Inner Mitochondrial membrane (Respiratory metabolism) \(\rightarrow \approx 25\%\) Lipid, \(75\%\) Protein.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Biological membranes are composed of proteins and lipids. The ratio of these components varies depending on the membrane's physiological function.

Step 2: Detailed Explanation:
- Assertion analysis: The myelin sheath is a specialized membrane layer that wraps around nerve axons to act as an electrical insulator, speeding up nerve impulse propagation. To prevent ion leakage and maximize insulation, myelin consists of up to \(75-80\%\) lipids and only \(20-25\%\) proteins, validating the Assertion.
- Reason analysis: The ratio of lipid to protein varies depending on membrane function. For example, the inner mitochondrial membrane is highly active in metabolic transport and electron transfer, consisting of \(75\%\) protein and \(25\%\) lipid. Myelin's high lipid content is a specific example of how membrane composition is adapted to its biological role.
- Because the Reason explains the functional basis of the myelin sheath's composition, (R) is the correct explanation of (A).

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).