Membrane models — According to the fluid mosaic model, what best describes the nature of biological membranes?
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Athe most common type of molecules in the membrane are proteins
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Bbasic membrane structure results from how the proteins interact with water
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Cthe membrane is a highly mobile mixture of phospholipids and proteins
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Dthe unique properties of cell types are determined by their phospholipids
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Emembranes are rigid lattices with fixed protein positions
Answer
Correct Answer: the membrane is a highly mobile mixture of phospholipids and proteins
Explanation
Introduction:The fluid mosaic model is a cornerstone of membrane biology. This question assesses whether you can articulate the model's central idea: lateral fluidity of lipids and proteins forming a dynamic, heterogeneous mosaic.
Given Data / Assumptions:
- Typical eukaryotic plasma membrane.
- Key components: phospholipids and proteins; carbohydrates are present as glycoconjugates.
Concept / Approach:In the model, a phospholipid bilayer provides a fluid matrix into which proteins are inserted. Proteins and many lipids diffuse laterally; composition varies by membrane domain and leaflet.
Step-by-Step Solution:
1) Identify structural basis: bilayer of amphipathic phospholipids ensures barrier properties and fluidity.2) Recognize protein dynamics: integral and peripheral proteins move laterally (subject to constraints such as cytoskeletal anchoring and lipid rafts).3) Synthesize statement that captures both mobility and mosaic composition.Verification / Alternative check:Experiments such as FRAP (fluorescence recovery after photobleaching) demonstrate lateral diffusion of membrane proteins and lipids, validating the fluid aspect of the model.
Why Other Options Are Wrong:
- Proteins most common: by count and area, lipids dominate; proteins are abundant but not the majority by molecule number.
- Structure from protein–water interactions: the bilayer self-assembles from lipid amphipathic properties, not primarily protein–water interactions.
- Properties determined by phospholipids alone: protein composition strongly shapes function.
- Rigid lattices: contradicts extensive evidence for mobility.
Common Pitfalls:Equating fluidity with randomness; membranes have microdomains and cytoskeletal fences that regulate diffusion without eliminating overall fluid behavior.
Final Answer:the membrane is a highly mobile mixture of phospholipids and proteins.