Which statement best describes how alpha-helix and beta-sheet stability are determined?

Which statement best describes how alpha-helix and beta-sheet stability are determined?

• A. Alpha-helix is stabilized by intra-chain hydrogen bonds with defined geometry; beta-sheets stabilized by inter-strand hydrogen bonds and side-chain packing; overall stability depends on interactions.
• B. Alpha-helix stability is due solely to hydrophobic interactions; beta-sheets rely on disulfide bonds.
• C. Beta-sheets stability is due exclusively to hydrophobic core formation across membranes.
• D. There is no difference in stability between alpha-helix and beta-sheet.

Answer: (B)

Hydrogen bonding patterns and how side chains pack are the main determinants of secondary-structure stability. In an alpha-helix, the backbone rows form hydrogen bonds within the same chain every four residues, creating a regular, stabilized coil. This intrachain network fixes the helix geometry and is complemented by how the side chains fit together along the helical exterior. In a beta-sheet, stability comes from hydrogen bonds between adjacent strands, connecting carbonyls and amides across the sheet. The strands can run parallel or antiparallel, and tight side-chain packing between aligned strands adds further stabilization through favorable contacts and van der Waals interactions. Overall stability reflects the combination of these hydrogen-bond networks and the packing of side chains, along with contributions from the hydrophobic core and other interactions. Hydrophobic effects help drive folding but aren’t the sole stabilizing force, and disulfide bonds can stabilize specific proteins but aren’t the universal determinant of beta-sheet stability.

Hydrogen bonding patterns and how side chains pack are the main determinants of secondary-structure stability. In an alpha-helix, the backbone rows form hydrogen bonds within the same chain every four residues, creating a regular, stabilized coil. This intrachain network fixes the helix geometry and is complemented by how the side chains fit together along the helical exterior.

In a beta-sheet, stability comes from hydrogen bonds between adjacent strands, connecting carbonyls and amides across the sheet. The strands can run parallel or antiparallel, and tight side-chain packing between aligned strands adds further stabilization through favorable contacts and van der Waals interactions.

Overall stability reflects the combination of these hydrogen-bond networks and the packing of side chains, along with contributions from the hydrophobic core and other interactions. Hydrophobic effects help drive folding but aren’t the sole stabilizing force, and disulfide bonds can stabilize specific proteins but aren’t the universal determinant of beta-sheet stability.