Amino Acids & Proteins MCAT Practice Question
A biochemist studies a membrane protein with seven transmembrane helices. Analysis reveals that the hydrophobic core of each helix contains primarily leucine, isoleucine, and valine residues, while the protein-water interface includes serine, threonine, and lysine. What is the thermodynamic principle underlying this amino acid distribution?
Answer choices
- AHydrophobic residues are thermodynamically unstable and aggregate to minimize free energy
- BPolar residues denature at body temperature and must be buried in the hydrophobic core
- CThe hydrophobic effect drives nonpolar residues into the membrane interior, while polar residues interact favorably with water at the surfaceCorrect answer
- DLysine residues are required to bind membrane phospholipids at the interface
- EValine and leucine form covalent cross-links that stabilize the transmembrane helices
- FLeucine and isoleucine residues form hydrogen bonds with the lipid bilayer fatty acid chains, while lysine residues prevent membrane permeability
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