In sickle cell anemia, how does the hydrophobic effect contribute to the agglutination of hemoglobin molecules?

• A. Polar glutamate residues attract each other, causing clumping.
• B. Nonpolar valine residues repel each other, preventing clumping.
• C. Polar glutamate residues repel each other, preventing clumping.
• D. Nonpolar valine residues interact, causing hemoglobin molecules to clump together.

Answer: (D)