[Campbell Biology P.132] A polypeptide region is rich in amino acids like valine, leucine, a... | Practice Question

A polypeptide region is rich in amino acids like valine, leucine, and isoleucine. In a correctly folded polypeptide, where would you expect this region to be primarily located, and what could be a consequence if these regions are exposed to the aqueous solvent due to misfolding?

  • A: Primarily on the surface, interacting with the aqueous solvent, leading to increased protein solubility.
  • B: Primarily in the interior, shielded from the aqueous solvent; misfolding exposing them can lead to protein aggregation.
  • C: Equally distributed throughout the polypeptide; exposure due to misfolding has no significant consequences.
  • D: Primarily on the surface, forming strong covalent bonds with the solvent, stabilizing the protein.

Explanation

Valine, leucine, and isoleucine are well-known hydrophobic amino acids. In an aqueous environment like the cell , hydrophobic regions of a correctly folded protein typically fold inward to be shielded from the water, while hydrophilic regions face outward. If these hydrophobic regions are exposed due to misfolding, they tend to aggregate with other hydrophobic regions from other misfolded proteins, leading to protein aggregation. The text mentions that 'hydrophobic regions face outward toward the solvent' for denatured proteins, implying that normally they are inward, and that 'misfolding of polypeptides in cells is a serious problem' often associated with accumulation of misfolded proteins.