Collagen is a fibrous glycoprotein whose role can be compared to a frame. This is the most abundant protein in the body, representing a quarter of the protein mass of the body [precision needed]. It is secreted by cells of connective tissue and has a molecular weight of 300 kDa.

Unlike elastin also present in connective tissues, collagen is inextensible and good resistance to traction. It consists of different types according to their location. It is particularly essential to the healing process. After some transformations, we can make glue.

A structural protein
Biochemists know now more than 100 000 proteins. These molecules are involved in many processes. Some are at the heart of immunology. Others have an enzymatic activity essential for the proper functioning of the cellular machinery. Others are membrane receptors by which cells interact with the environment. Some, finally, participate in the structuring of organizations. This is the case of collagen, a protein essential connective tissue of animals.

A very abundant molecule
The proteins are separated into two categories. The functional proteins involved in biochemical processes (enzymology, immunology, membrane receptors, etc..). The structural proteins are shaping organizations contributing to their structure. Among these, collagen is particularly representative. This fibrous protein is by far the most abundant among all mammals, accounting for one fourth of their protein, about 5% of their weight.

A natural glue
When collagen is partially hydrolyzed, the three tropocollagen strands dissociate. They form the gelatin, a product widely used in food processing. Gelatin was also used in pharmaceuticals, cosmetics and photography. Collagen and gelatin are considered poor protein nutritional quality because they do not have all the amino acids in proper proportions.

The word collagen means "glue producer" (the name is in fact a Greek word kolla meaning glue). The properties of collagen have been used by the Egyptians there are 4 000 years. The Indians used it it is 1 500 years. The oldest known glue is made from collagen, and date of 8 000 years. Currently it is used in the products of beauty or as an additive in chicken.

The tropocollagen
The tropocollagen is the basic unit of collagen, and corresponds to a molecule asymmetric 280nm in length and 1.5 nm in diameter. It is a glycoprotein formed by winding 3 propellers left not α, carriers of carbohydrate (glucose, galactose). Amino acids are made for one third of glycine for one quarter of proline, hydroxylysine and 4-hydroxyproline. There are several types of molecular chains α. These channels are formed by repetitive sequences of three amino acids, of which the first glycine is repeated throughout the molecule. Carbohydrates are attached to hydroxylysine. The winding of 3 α chains, resulting in the formation of the tropocollagen molecule, whose cohesion is ensured by hydrogen bonds between glycine and hydroxyproline.

See also Vitamin C