Collagen's molecular structure and properties

Steps:

• Recall collagen is a fibrous protein with a triple helix formed by three polypeptide chains.
• Identify key amino acids: every third is glycine, enabling tight packing.
• Note collagen's insolubility and assembly into fibrils via quaternary interactions.
• Evaluate statements against these facts to find the accurate one.

Why B is correct:

• Collagen is defined as an insoluble fibrous protein that assembles multiple subunits into fibrils, exhibiting quaternary structure through intermolecular cross-links.

Why the others are wrong:

• A: The helices are staggered in a triple helix, stabilized by hydrogen bonds and covalent cross-links, not just parallel helices with hydrogen bonds.
• C: One-third of amino acids are glycine (Gly-X-Y repeats), not valine.
• D: Fibers form via covalent cross-links between molecules, not ionic bonds.

Final answer: B