Membrane sterols such as cholesterol function in animal cell membranes to ____.

Question

BlackTom AI · Accepted Answer

Cholesterol intercalates between phospholipid molecules in the bilayer and thereby helps maintain membrane fluidity.

1) Relevant knowledge points and concepts
- Fluid mosaic model: membranes are a fluid layer of phospholipids with embedded proteins; fluidity is crucial for protein mobility and membrane function.
- Phospholipid tail packing: saturated tails pack tightly (less fluid); unsaturated tails create kinks (more fluid).
- Cholesterol as a membrane sterol: amphipathic molecule that inserts with its hydroxyl near the polar head groups and its rigid ring structure among fatty acid tails.
- Temperature dependence: membranes become more fluid at high temperature and more rigid (gel phase) at low temperature.

2) Step-by-step reasoning
- Cholesterol fits between phospholipid tails, restricting their movement when the membrane would otherwise be too fluid (high temperature).
- At low temperatures, cholesterol prevents phospholipids from packing too closely, because its bulky rigid rings interrupt tight tail packing.
- Thus cholesterol acts as a bidirectional buffer: it decreases excessive fluidity at high temperatures and prevents solidification at low temperatures — overall maintaining an optimal intermediate fluidity.

3) Intermediate conceptual steps (no numeric calculations required)
- Insert cholesterol → reduces lateral mobility of phospholipid tails when tails would be highly mobile.
- Insert cholesterol → increases spacing/order defects when tails would otherwise pack tightly at low T.
- Net effect → stabilization of membrane viscosity and permeability across temperatures.

4) Why the correct answer is correct
- The described physical interactions explain how cholesterol controls membrane dynamics: by modulating packing and movement of lipid tails, cholesterol preserves membrane fluidity necessary for transport, signaling, and protein function.

5) Why other choices would be incorrect (common distractors)
- “Provide most structural support” is wrong: proteins and the cytoskeleton largely provide structural support; cholesterol modulates fluidity and stability but is not the main structural scaffold.
- “Serve as membrane receptors” is wrong: cholesterol is not a receptor; some proteins and glycoproteins perform receptor roles.
- “Increase permeability” is wrong: cholesterol typically decreases membrane permeability to small polar molecules by filling gaps between lipids.

6) Conclusion
These mechanisms confirm that membrane sterols such as cholesterol function to maintain membrane fluidity, matching the provided answer.

Membrane sterols such as cholesterol function in animal cell membranes to ____.单项选择题

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