Hydrophobic proteins and water: If a protein were built exclusively from nonpolar amino acids, how would it interact with water?
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AIt would be repelled by water (strongly hydrophobic).
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BIt would be strongly attracted to water.
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CIt would spontaneously form a lipid membrane.
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DIt would act as a buffer to stabilize pH.
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EIt would dissolve and increase osmotic pressure only.
Answer
Correct Answer: It would be repelled by water (strongly hydrophobic).
Explanation
Introduction / Context:Protein–water interactions drive folding and function. Nonpolar amino acids (for example, leucine, isoleucine, valine, phenylalanine) avoid contact with water, a phenomenon underlying the hydrophobic effect.
Given Data / Assumptions:
- Hypothetical protein composed exclusively of nonpolar side chains.
- Environment: aqueous solution.
- No detergents or chaperones present.
Concept / Approach:Water forms a hydrogen-bonded network; nonpolar surfaces disrupt it without compensating interactions. To minimize this disruption, nonpolar residues cluster together, reducing exposed hydrophobic surface area. Thus, an all-nonpolar protein would be extremely insoluble and “repelled” by water, aggregating or partitioning into nonpolar phases.
Step-by-Step Solution:Identify the side chain chemistry: nonpolar = hydrophobic.Predict solubility: poor in water, tendency to aggregate.Choose the option indicating repulsion from water.
Verification / Alternative check:Membrane proteins bury nonpolar regions within lipid bilayers and expose polar regions to water; all-nonpolar sequences are typically membrane-embedded or insoluble aggregates.
Why Other Options Are Wrong:
- Attracted to water/buffer behavior: Requires polar/ionizable groups.
- Spontaneous lipid membrane formation: Lipids, not proteins, form bilayers.
Common Pitfalls:Confusing hydrophobic aggregation of proteins with membrane self-assembly by amphipathic lipids.
Final Answer:It would be repelled by water (strongly hydrophobic).