The middle part of the procollagen chain, has the conformation of a left-handed, highly elongated helix which is completed on both sides with non-sinuous sections, the so called N-and C-terminal propeptides. These fragments are responsible for the correct transport and aggregation of the individual chains. Thanks to the intra- and intermolecular disulfide bridges in the terminal propeptides, the three chains of procollagen are being stored parallel together, which leads to the distortion in the middle part to the right. Such procollagen is a subject to the secretion through the cell membrane, and both terminal fragments are split off by two endopeptidases. In this way, a mature tropocollagen arises, which polymerizes by longitudinal and transverse bonds spontaneously into fibrils. The conformation of the molecule is maintained by weak (hydrophobic, electrostatic, and hydrogen bond forces) as well as by strong agents (ionic and covalent forces between the alpha chains, which create the tropocollagen). The tropocollagen (mature collagen molecule) can be a homotrimer composed of three identical chains, or a heterotrimer, which consists of 2 or 3 different chains. Because of the biological attributes, atoxicity and biocompatibility with all living organisms as well as with the massive adoption, the collagen is used as a biological material in the medical, pharmaceutical and cosmetic industries. Collagen is not a static protein. During the entire life, in the organism it comes to a constant collagen replacement. The old fibers disintegrate and are replaced by new ones. After the age of 25, the phases of the collagen in the skin begin to decay faster, than the new ones are being created. This process is still increasing with age. The natural aging process leads to visible effects. In the beginning, a slight drying of the skin and facial wrinkles are noticeable. That process deepens with the time. In addition, various factors such as UV radiation, cigarette consumption, pollution, prolonged work at the computer screen, stress and wrong diet methods lead to premature destruction of the natural collagen structure. It was inter alia proven, that a large dose of radiation destroys the natural structure of collagen, which may lead to its denaturation. The previous studies showed that collagen solutions under the influence of UV rays lose their ability to form fibrils, and the result of photochemical processes is both integration and degradation. The main chromophores which absorb UV radiation in the collagen are two aromatic amino acids: tyrosine and phenylalanine. The type of photochemical reaction and efficiency also depends on the presence of other substances which occur along with this protein. The collagen type I (2 [alpha1I] alpha2) is composed of two alpha1-peptide chain type I and one alpha2 chain type I. The collagen type I is the typical representative of the collagen in the skin of mammals (in the connective tissue, it is connected to the particles of the mucopolysacharide).
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