Spider silk's strength from beta-sheet secondary structure

Steps:

• Identify spider silk as a protein fiber with repeating glycine-alanine sequences.
• Recognize these sequences promote hydrogen bonding to form beta-pleated sheets.
• Classify beta-pleated sheets as secondary protein structure, stabilized by backbone interactions.
• Confirm this matches the structural description for silk's tensile properties.

Why B is correct:

• Beta-pleated sheets define secondary structure via parallel or antiparallel polypeptide strands linked by hydrogen bonds, as in spider silk fibroins.

Why the others are wrong:

• A: Primary structure is the linear amino acid sequence; spider silk exhibits folded secondary elements.
• C: Tertiary structure involves 3D folding of one chain; spider silk emphasizes beta-sheet arrays over single-chain folds.
• D: Quaternary structure requires multiple protein subunits; spider silk forms from single-chain assemblies.

Final answer: B