Collagen's structural features

Steps:

• Identify collagen as a fibrous protein with a triple helix structure.
• Note stabilization by hydrogen bonds, not disulfide bonds.
• Recall high content of glycine, proline, and hydroxyproline, making it insoluble in water.
• Match these to choice descriptors: bonds, solubility, composition, helix type.

Why C is correct:

• Collagen forms a triple helix stabilized by hydrogen bonds, is insoluble in water, and consists mainly of three amino acids (glycine, proline, hydroxyproline), per its repeating Gly-X-Y sequence.

Why the others are wrong:

• A: Disulfide bonds and double helix describe keratin, not collagen's triple helix.
• B: Disulfide bonds and single helix apply to other proteins; collagen has hydrogen bonds and triple helix.
• D: Collagen is insoluble in water and features a triple helix, not an alpha helix.

Final answer: C