Question

Which of the following is present in the mammalian plasma membrane but absent in most of the prokaryotic cell membrane?

• A. Cholesterol
• B. Phospholipids
• C. Carbohydrate
• D. Protein

Hint:

Membrane Sterols: Eukaryotes = Cholesterol Ergosterol. Bacteria = Hopanoids (NO cholesterol, except Mycoplasma).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Membrane lipid composition differences distinguish eukaryotic plasma membranes from eubacterial membranes.

Step 2: Detailed Explanation:
1. Cholesterol (Sterols): Major rigid planar lipid constituent ($30-40\%$ of lipid bilayer) of mammalian plasma membranes, regulating fluidity across physiological temperatures.
2. Prokaryotes: Most bacterial membranes completely lack cholesterol and sterols (with rare exceptions like Mycoplasma which scavenge sterols from the host). Instead, bacteria use pentacyclic triterpenoids called hopanoids to stabilize membrane fluidity.

Step 3: Final Answer:
Therefore, Cholesterol is present in mammalian membranes but absent in most prokaryotes, corresponding to option (A).