Multiple Choice
In a phospholipid bilayer, what is the primary role of cholesterol?
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8. Membrane Structure
The Lipid Bilayer
Multiple Choice
In the context of the lipid bilayer, where is cholesterol typically found within the cell membrane?
A
Intercalated between phospholipid molecules in the hydrophobic core, with its hydroxyl group near the polar head groups
B
Exclusively in the aqueous cytosol, functioning only as a soluble carrier for fatty acids
C
Covalently attached to the extracellular domains of transmembrane proteins as a carbohydrate-like modification
D
Only on the outer leaflet surface, fully exposed to the extracellular fluid and not embedded in the bilayer
Verified step by step guidance1
Understand the structure of the lipid bilayer: it consists of two layers of phospholipids with hydrophilic (polar) head groups facing outward towards the aqueous environments and hydrophobic (nonpolar) tails facing inward, creating a hydrophobic core.
Recall the chemical nature of cholesterol: it has a hydrophobic steroid ring structure and a small hydrophilic hydroxyl (-OH) group.
Consider how cholesterol interacts with the lipid bilayer: its hydrophobic rings align with the fatty acid tails of phospholipids in the hydrophobic core, while its hydroxyl group orients near the polar head groups to interact with the aqueous environment.
Evaluate the options given: cholesterol is not soluble in the aqueous cytosol, nor is it covalently attached as a carbohydrate-like modification, and it is not only on the outer leaflet fully exposed to extracellular fluid.
Conclude that cholesterol is typically intercalated between phospholipid molecules within the hydrophobic core of the membrane, with its hydroxyl group positioned near the polar head groups.
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