Explain how the fluid mosaic model accounts for the lateral movement of membrane proteins and discuss why this movement is physiologically significant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The phospholipid bilayer is fluid – the hydrophobic tails are not rigidly fixed, so components can move laterally within each leaflet.
Integral (transmembrane) and peripheral proteins are embedded in or associated with this fluid bilayer and therefore diffuse laterally unless they are anchored to the cytoskeleton.
This lateral movement allows receptor proteins or transporters to cluster or redistribute, enabling cell signalling, formation of receptor complexes, or concentration of transporters at specific membrane domains (e.g. synaptic membrane, leading edge of a migrating cell).
It also facilitates membrane repair and resealing after damage, as phospholipids and proteins can flow into disrupted regions, restoring bilayer integrity.
Integral (transmembrane) and peripheral proteins are embedded in or associated with this fluid bilayer and therefore diffuse laterally unless they are anchored to the cytoskeleton.
This lateral movement allows receptor proteins or transporters to cluster or redistribute, enabling cell signalling, formation of receptor complexes, or concentration of transporters at specific membrane domains (e.g. synaptic membrane, leading edge of a migrating cell).
It also facilitates membrane repair and resealing after damage, as phospholipids and proteins can flow into disrupted regions, restoring bilayer integrity.
Examiner tips
- Use the phrase "fluid bilayer" and mention "hydrophobic tails" to show understanding of fluidity. Explain that proteins are free to diffuse unless anchored. Give at least one physiological example (e.g. signalling, transport concentration, repair).
- Use clear, concise sentences and avoid unnecessary words. Keep each point brief but complete.
Mark scheme (4 marks)
- The phospholipid bilayer is fluid / the hydrophobic tails are not rigidly fixed, allowing components to move laterally within each leaflet.
- Membrane proteins (both integral/transmembrane and peripheral) are embedded within or associated with this fluid bilayer and are therefore free to diffuse laterally unless anchored to the cytoskeleton.
- Lateral movement allows receptor proteins or transport proteins to cluster / redistribute, enabling cell signalling, formation of receptor complexes, or concentration of transporters at specific membrane domains (e.g. synaptic membrane, leading edge of a migrating cell).
- Lateral movement also facilitates membrane repair and resealing after damage, as phospholipids and proteins can flow into disrupted regions, restoring bilayer integrity.
Key terms in this question
fluid mosaic model · lateral movement
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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