Hemoglobin and silk fibroin are proteins with distinct secondary structures. How do these structures relate to their biological roles?

• A. Hemoglobin's beta sheets allow for oxygen binding, while silk fibroin's alpha helices provide tensile strength.
• B. Both hemoglobin and silk fibroin rely mainly on beta sheets for flexibility.
• C. Both hemoglobin and silk fibroin rely mainly on alpha helices for rigidity.
• D. Hemoglobin's alpha helices allow for oxygen binding, while silk fibroin's beta sheets provide tensile strength.

Answer: (D)