2 English reference collagen
Collagen is an extracellular fibrous protein, which is responsible for the strength and elasticity of connective tissue.
3 Distribution and Function Collagen accounts for almost 65,438+0/3 of the total protein of vertebrates, and is the richest protein in the body. The bigger the animal, the greater the proportion of collagen in protein. Cows, for example, are mainly made up of strong collagen in leather, tendons, cartilage and bones. Collagen not only anchors and supports cells, but also provides a suitable microenvironment for cell growth and participates in physiological processes such as cell migration, differentiation and proliferation.
Structural collagen is arranged into fibers visible under optical microscope, and the latter is composed of microfibers visible under electron microscope. These microfibers have characteristic transverse stripes and are arranged in different forms due to different biological functions of connective tissue. For example, collagen fibers are arranged in parallel bundles in tendons and interwoven into nets in leather. The organic matter in cornea is almost pure collagen. Collagen contains an unusually high proportion of glycine (about 35%), alanine (about 1 1%), proline and rare hydroxyproline (the latter two add up to about 2 1%), while other amino acids are very few. Collagen fibers are composed of many protein called procollagen. Precollagen molecules are arranged in parallel bundles from end to end, and their heads are staggered back and forth along the fiber length direction, and the overlapping part just shows the characteristic 64 nm interval of most collagen fibers. X-ray diffraction analysis shows that procollagen contains three polypeptide chains with a length of 300 nm and a thickness of 65438±0.5nm, and each polypeptide chain contains about 65438 0000 amino acid residues. In some collagen, the amino acid sequences of these three chains are the same; In other collagen, the amino acid sequences of the two peptide chains are the same. All three polypeptide chains are left-handed helices, and each ring contains only three amino acid residues. They are closely intertwined and crosslinked by hydrogen bonds and unusual valence bonds composed of lysine. Adjacent collagen 3 helices are also crosslinked, so collagen cannot be extended.
5 Properties and Application With the increase of age, more and more * * valence cross-linking bonds are generated in or between procollagen molecules, which makes collagen microfibers in connective tissue harder and more brittle, thus changing the mechanical properties of tendons and cartilage, and easily causing fractures and corneal opacity. There are many genetic and environmental factors that lead to impaired collagen synthesis, which can cause diseases, such as osteogenesis imperfecta, and the lack of vitamin C also hinders the production of collagen. Collagen is insoluble in water and cannot be digested under physiological conditions; However, when boiled in water, it can be converted into a mixture of soluble peptides, called gelatin, which is used as the matrix of gel food because of the hydrolysis of some valence bonds. Because of the incomplete types of essential amino acids, the nutritional value of gelatin itself is very low. The reason why meat can't be chewed is caused by collagen in connective tissue and blood vessels, so meat must be cooked before eating. Stored soft and tender meat products often contain plant enzymes, which can hydrolyze some peptide bonds in collagen and convert them into digestible soluble polypeptide mixtures.