Which of the following statements correctly describes the shape of the two secondary protein structures, α helix and a β-pleated sheet?

• A. The α helix is an extended, sheet-like structure stabilized by inter-chain hydrogen bonds, while the β-pleated sheet is a compact, spiral structure stabilized by intra-chain sulfide bonds.
• B. The α helix is a compact, spiral structure stabilized by intra-chain sulfide bonds. At the same time, the β-pleated sheet is an extended, sheet-like structure stabilized by inter-chain dispersion forces only.
• C. The α helix is a compact, spiral structure stabilized by intra-chain hydrogen bonds, while the β-pleated sheet is an extended, sheet-like structure stabilized by inter-chain hydrogen bonds.
• D. The α helix is an extended, sheet-like structure stabilized by inter-chain hydrogen bonds. At the same time, the β-pleated sheet is a compact, spiral structure stabilized by intra-chain dipole-dipole interactions.

Answer: (C)