NB

HNB Collagen like all proteins is made up of amino acids. The collagen protein is composed of a triple helix, which generally consists of two identical chains (α1) and an additional chain that differs slightly in its chemical composition (α2).^[1] The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content. The most common motifs in the amino acid sequence of collagen are glycine-proline-X and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline or hydroxyproline. The average amino acid composition for fish and mammal skin is given.^[1] 

^[1] Szpak, Paul (2011). "Fish bone chemistry and ultrastructure: implications for taphonomy and stable isotope analysis". Journal of Archaeological Science. 38 (12): 3358–3372.doi:10.1016/j.jas.2011.07.022.