Collagen is a kind of protein family. At present, it has been found that at least 30 kinds of genes encoding collagen chains can form more than 16 kinds of collagen molecules. Collagen can be divided into fibrous collagen, basement membrane collagen, microfibril collagen, anchor collagen, hexagonal collagen, non-fibrous collagen and transmembrane collagen according to its structure. According to their distribution and functional characteristics in the body, collagen can be divided into interstitial collagen, basement membrane collagen and cell peripheral collagen. Interstitial collagen molecules account for the vast majority of whole body collagen, including type ⅰ, ⅱ and ⅲ collagen. Type I collagen is mainly distributed in skin, tendons and other tissues, and it is also the most abundant aquatic product processing waste (skin, bone and scale) in protein, accounting for about 80-90% of the total collagen content, and is widely used in medicine. One of the most remarkable characteristics of fish collagen I is its low thermal stability and species specificity. Type ⅱ collagen is produced by chondrocytes; Collagen in basement membrane usually refers to type ⅳ collagen, which is mainly distributed in basement membrane; Collagen in peripheral cells usually refers to type ⅴ collagen, which is rich in connective tissue. Collagen can be divided into two groups according to their functions. The first type is fibroblast collagen, including collagen types I, II, III, VIII, VIII, VIII and VIII. The rest is the second group, non-fibrotic collagen. The α chain of non-fibrotic collagen contains both triple helix domain (COL) and non-triple helix domain (NC), in which fibrotic collagen accounts for about 90% of the total collagen.

Types of collagen and its distribution in tissues.