Which statement best describes the hydrogen bonding patterns of alpha-helices and beta-sheets?

• A. Alpha-helix has intra-chain hydrogen bonds every fourth residue in a right-handed geometry, while beta-sheets are held together by inter-strand hydrogen bonds and can be parallel or antiparallel.
• B. Alpha-helix forms inter-strand hydrogen bonds between different polypeptide chains; beta-sheets rely on intra-chain bonds within a single strand.
• C. Alpha-helix is stabilized primarily by disulfide linkages; beta-sheets rely on ionic bonds between side chains.
• D. Alpha-helix and beta-sheet use identical hydrogen bonding patterns; the only difference is their overall shape.

Answer: (A)