Multiple Choice
In the context of the lipid bilayer, what is another name for the cell membrane?
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8. Membrane Structure
The Lipid Bilayer
Multiple Choice
Which statement about the lipid bilayer of the cell membrane is true?
A
Most membrane proteins freely diffuse across the bilayer by flipping between leaflets (transverse diffusion) without assistance.
B
Cholesterol decreases membrane fluidity at all temperatures by tightly packing phospholipid tails.
C
Phospholipids arrange with hydrophilic heads facing the aqueous environment and hydrophobic tails facing inward toward each other.
D
The lipid bilayer is a rigid, covalently cross-linked sheet that prevents any lateral movement of membrane components.
Verified step by step guidance1
Understand the structure of the lipid bilayer: it is composed mainly of phospholipids arranged in two layers (leaflets). Each phospholipid has a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.
Recall that phospholipids spontaneously arrange themselves so that the hydrophilic heads face the aqueous environments both inside and outside the cell, while the hydrophobic tails face inward, away from water, creating a stable bilayer.
Consider membrane protein movement: most proteins do not flip between leaflets (transverse diffusion) easily because this process requires moving hydrophilic regions through the hydrophobic core, which is energetically unfavorable and usually assisted by enzymes called flippases.
Evaluate the role of cholesterol: it modulates membrane fluidity by preventing phospholipid tails from packing too tightly at low temperatures and restraining movement at high temperatures, thus maintaining fluidity rather than decreasing it at all temperatures.
Recognize that the lipid bilayer is fluid and dynamic, allowing lateral movement of lipids and proteins; it is not a rigid, covalently cross-linked sheet, so lateral diffusion is common and essential for membrane function.
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