Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : The lipid present in the membrane produces a closed vesicle in aqueous medium.
Reason (R) : Membrane lipids carries only positive charge and are highly soluble in water.
In light of the above statements, 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 false.
• D. (A) is false but (R) is true.

Hint:

The spontaneous formation of closed lipid vesicles (liposomes) in water is driven by the hydrophobic effect, which maximizes entropy by sequestering nonpolar hydrocarbon tails away from water molecules.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Membrane lipids are amphipathic molecules, meaning they possess both a hydrophilic (polar) head group and hydrophobic (nonpolar) hydrocarbon tails.
Their behavior in an aqueous environment is driven by the hydrophobic effect.
Detailed Explanation:
- Evaluating Assertion (A): When amphipathic lipids (such as glycerophospholipids and sphingolipids) are placed in water, they spontaneously assemble into bilayers to minimize the free energy of the system.
To completely eliminate exposure of the hydrophobic edges of the sheet to water, the bilayer folds in on itself to form a closed, spherical vesicle (such as a liposome). This is the thermodynamic basis for membrane self-assembly. Thus, Assertion (A) is true.
- Evaluating Reason (R): Membrane lipids are not highly soluble in water; their large hydrophobic tails make them highly insoluble.
Furthermore, they carry different charges: some are zwitterionic (neutral at physiological pH, e.g., phosphatidylcholine), some carry a net negative charge (e.g., phosphatidylserine, phosphatidylinositol), and some are neutral. They do not carry only positive charges. Thus, Reason (R) is false.

Step 2: Final Answer:
Assertion (A) is true but Reason (R) is false. This corresponds to option (C).