Collagen's variable genetic coding

Steps:

• Collagen molecules form a triple helix from three polypeptide chains.
• These chains can be identical, all from one gene type I collagen.
• Or two identical and one different, from two genes like type III.
• Or all three different, from three genes like type V.

Why D is correct:

• Collagen's quaternary structure allows homotrimers (1 gene), heterotrimers with two types (2 genes), or three types (3 genes), per molecular biology definitions.

Why the others are wrong:

• A limits to only homotrimers, ignoring heterotrimeric collagens.
• B restricts to two-chain variants, excluding homotrimers and three-chain types.
• C confines to three different chains, overlooking simpler one- or two-gene forms.

Final answer: D