Collagen: what it is, types and characteristics

Living beings are made up of many different chemical substances (between 25 and 30), but 96% of the mass of most cells is made up of the following bioelements essential: carbon (C), hydrogen (H), oxygen (O), sulfur (S), nitrogen (N) and phosphorus (P), which are much more abundant in living organic matter than in the other elements of the crust land.

Proteins, macromolecules formed from linear chains of amino acids, are the basis of all living tissue., since they represent 80% of the dehydrated cell protoplasm and 50% of the dry weight of all tissue associations in the body. Genes, enclosed in the nucleus in the form of chromosomes, encode through nucleic acid sequences the synthesis of specific proteins. Thanks to the mechanisms of transcription and translation, the genetic code becomes the functional elements that shape our body.

Some 500 types of amino acids have been identified, but only 20 are part of the proteins of the human organism, that is, they are encoded at the genetic level. In any case, the number of linked amino acids, the order in which each of them is placed, the conformation of the chains and the prosthetic (non-protein) groups provide an incomprehensible variety of proteins in just one an organism. Today we tell you everything about one of the most important:

collagen.

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What is collagen?

Collagen is the most abundant fibrous protein in the extracellular matrix and connective tissue. It is one of the main components of skin and bones and therefore covers approximately 25% of the protein mass of the human organism. It is also found in tendons, ligaments, and cartilage. Depending on the degree of mineralization, collagen can be rigid, malleable, or somewhere in between.

Collagen is a protein and, therefore, it is made up of amino acids. Amino acids are the basic protein subunits that are joined by peptide bonds: when associate from 2 to 10 the compound is called a peptide, from 10 to 50 it is a polypeptide and from 50 it is a protein. The genetic code is universal, which means that the information that encodes the placement of an amino acid when assembling a protein is the same in all living beings.

In general, this very special protein is in the form of a triple helix, composed of two identical polypeptide chains α1 and one that differs slightly from them (α2). The most common repeat motif of collagen is as follows:

Glycine-proline-X // glycine-X-hydroxyproline

It should be noted that "X" is any amino acid that is not any of the 3 mentioned. Due to this conformation, collagen it is rich in the amino acids glycine, proline and hydroxyproline. Above all, this last amino acid differentiates it from the rest of the protein elements, since it is not usual for a protein to have so much hydroxyproline in its polypeptide skeleton. For example, human collagen contains 329 glycine, 126 proline, and 95 hydroxyproline units per 1,000 amino acid residues.

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Collagen Types

We have talked about collagen as a unique and invariable protein, but nothing could be further from the truth. Depending on the type of chains they present, their arrangement, their location and the interrelationship with other elements, various types of collagen can be detected.. Among them, we highlight the following:

• Type I collagen, α1, α1, α2(I) chains: forms 90% of body collagen. It is found in the skin, bones, tendons, ligaments, dentin, and cornea.
• Type II collagen, [α1(II)]3 chains: found in hyaline cartilage, vitreous humor, and notochord, the cartilaginous cord of chordates, which develops in the vertebral column in humans.
• Type III collagen, [α1(III)]3 chains: located in the skin, in blood vessels and as part of the tissues of internal organs.
• Type V collagen, α1, α1, α2-α3(V) chains: skin, bone, placenta and fetal membrane.
• Type X collagen, [α1(X)]3 chains: while those mentioned up to now appear in the form of fibers, this one forms hexagonal networks. It is part of the bone under construction.
• Collagen XIV, α1(XIV)3 chains: it is found associated with fibers, specifically in the skin, cornea, and articular cartilage.

We could continue citing examples, since we leave collagens IV, VI, VII, VIII, IX, XI, XII and others in the dark, since there are a total of 22. In any case, the idea is clear: this protein It is made up of different types of chains and, depending on their arrangement (fibers, networks, hexagonal networks, associated with fibers or transmembrane), several types of collagen can be counted., with different functionalities.

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common generalities

It can be very confusing to incur in such specific terminology, since it is easy to get lost between chains, polypeptides and synthesis zones. For this reason, we collect a series of basic ideas in relation to collagen in the following list:

• All types of collagen present the glycine-proline-X repeated motif and are composed of 3 interconnected chains, with different characteristics in each case.
• The various types of collagen differ primarily by their ability to form fibers, networks, or for the purpose of serving as connecting points between them.
• Most of the collagen in the body is arranged in the form of fibers and falls into the category of type I collagen.
• Collagen is not synthesized directly, since it is conceived in the form of procollagen, to later undergo a glycosylation process and give rise to the triple helix.
• Fibrous collagen has very specific morphological requirements and is therefore susceptible to mutations. This can translate into various clinical pictures.

What is the function of collagen?

Collagen is uOne of the main parts of connective tissue, since it is synthesized and secreted by fibroblasts, very abundant in these tissue associations. As its name indicates (connective, connection), collagen and the rest of the cell bodies associated with these tissues They are intended to connect body structures and hold them together, thus giving rise to the three-dimensional shape of the body. human.

collagen It has a high tensile strength, which makes it a prime candidate for forming part of fascia, cartilage, ligaments, skin, tendons, and bone.. In addition, together with keratin and elastin, it is the cause of the plasticity and deformability of the skin. Beyond type I, collagen XVII is another of the most important, since it is the junction point between the dermis and the epidermis.

In addition, it should be noted that collagen accompanies us beyond the locomotor system and the skin, as it is also part of key structures during fetal development, blood vessels, intervertebral discs and even the cornea. Without going any further, the stroma, the thickest part of the ocular cornea, is made up of about 200 interconnected collagen fibers. Without this protein, seeing properly would be impossible.

For all these reasons, it is not surprising that many of the mutations associated with collagen-coding genes result in serious pathologies. Also, because single-strand mutations can affect healthy collagen fibers, these mutations are considered dominant (they are expressed even if one of the two copies of the gene is fury). Ankylosing spondylitis, dermatomyositis, scleroderma, psoriatic arthritis and many other diseases are associated with collagen in one way or another.

Summary

In summary, collagen is a type of protein that can take up to 22 different forms, depending on the chains that compose it, the order of the amino acids, the relationship with the rest of the cellular elements and the place of location. Although up to 9 out of 10 collagen fibers are type I, they all play an essential role in long-term well-being.

Also, collagen is part of the skin, so it is often associated with anti-aging products and rejuvenating creams. Aging, smoking, exposure to ultraviolet radiation and other events can reduce the production of collagen and degrade the existing one, which gives rise to wrinkles and the typical appearance during senescence.