Which of the following always comprises 1/3 of the collagen structure?

Which of the following always comprises 1/3 of the collagen structure?

• A. Tyrosine
• B. Lysine
• C. Glycine
• D. Trytophan

Answer: (C)

Collagen typically has a repeating Gly-X-Y sequence, so about one third of its amino acids are glycine. The interior of the collagen triple helix is extremely crowded, with three chains packed together so tightly that only the smallest side chain can fit in the central core. Glycine has just a hydrogen as its side chain, allowing the three chains to come very close and form a stable triple helix. Bulky side chains would cause clashes and destabilize the interior packing, so amino acids with larger side chains don’t occupy that every-third position. That’s why glycine consistently makes up roughly one third of collagen’s structure.

Collagen typically has a repeating Gly-X-Y sequence, so about one third of its amino acids are glycine. The interior of the collagen triple helix is extremely crowded, with three chains packed together so tightly that only the smallest side chain can fit in the central core. Glycine has just a hydrogen as its side chain, allowing the three chains to come very close and form a stable triple helix. Bulky side chains would cause clashes and destabilize the interior packing, so amino acids with larger side chains don’t occupy that every-third position. That’s why glycine consistently makes up roughly one third of collagen’s structure.