Collagen fibers are an essential component of the body as it is a type of protein. This BeautiSecrets article provides you with some interesting information about these naturally occurring proteins.
As it is well-known, collagen fibers are naturally occurring proteins found exclusively in animals, mainly in the form of proteins in the connective tissues. It is the most commonly found protein in mammals and makes up about 25 – 35% of the whole body protein. Since the 1930s, scientists have been performing active research on the conformation of the collagen monomer, which is sheet-like or microfibrillar. This monomeric structure of the collagen fibers was described by Fraser, Miller, and Wess on close observation. The collagen molecule is also called the ‘tropocollagen’ and is an aggregate of the larger collagen fibrils.
Tropocollagen is approximately 300 nm in length and 1.5 nm in diameter. It is made up of polypeptide strands known as the alpha chains, and each of them is a left-handed helix in conformation. There are three such left-handed helices, which are twisted together to form a right-handed triple helix or superhelix, which is bonded to each other with hydrogen bonds. The entire molecule which is collectively called the collagen fiber is made up of a regular arrangement of amino acids, and hence, it is called a protein.
Types of Collagen Fibers
Throughout the body, there are 29 types of collagen that have been identified till date. However, more than 80% of the collagen in the body are of the types I, II, III, and IV. Each type is found in different parts of the body.
- Collagen type I is found in the skin, organs, bones, and tendons.
- Type II is found in cartilages all over the body.
- Type III is a major component of reticular fibers and along type I.
- The type IV is found in the cell basement membrane.
Collagen Fiber Formation
They are formed in vivo (inside the cell), but you can make it in vitro (outside the cell).
- The three peptide chains are formed in the ribosomes along the rough endoplasmic reticulum (RER), and these peptide chains have a registration peptide on one end and a signal peptide on the other end.
- These peptide chains are sent to the lumen of the RER where the signal peptides cleave and these chains are called procollagen.
- Then occurs the hydroxylation of the amino acids like lysine and proline which depends on ascorbic acid as a cofactor.
- Then glycosylation of these hydroxylated amino acid takes place, and the triple helical structure of the collagen monomer is formed inside the RER.
- This procollagen is then moved to the golgi apparatus where it is packed to make the collagen fibers and secreted by exocytosis.
- When they are formed outside the cell or in the lab, the registration peptides are cleaved and the tropocollagen is formed by the procollagen peptidase.
- These multiple molecules of the tropocollagen together form the fibers by covalent cross-linking of the lysine residues.
- These fibers are attached to the cell membranes through fibronectin and integrin proteins.
As they are found in the connective tissues and extracellular matrix of the cells, their main function is to support all the tissues around the cell and give the cells a structure from the outside. As it has excellent tensile strength, it is the main component of cartilages, tendons, ligaments, and the skin. It also strengthens the blood vessels and develops many tissues in our body.