Proteins (proteins) - a natural organic compound whose molecules have the form of long chains composed of amino acidslinked by peptide bonds.
The compounds of amino acids called polypeptides, and alreadypolypeptides , in turn, connecting with one another to form complex protein molecules.
The structure of proteins consists of carbon, hydrogen, oxygen, nitrogen, sulfur and sometimes phosphorus . The most characteristic for the presence of protein in the molecule of nitrogen (other nutrients do not contain nitrogen).
Proteins are the basic and most complex in their composition substances obtained from human food. In the gastrointestinal tract of food proteins are broken down to amino acids that the human body uses to synthesize their own proteins.
By connecting with each other or with nucleic acids, polysaccharides , and lipids , proteins form different structures in which there are multiple metabolic processes. Protein foods can not be replaced by any other nutrient, because synthesis of proteins necessary for an organism, it is possible only from amino acids. Deficiency of protein in the diet leads to a deterioration of immunity, the emergence of various disturbances in the cardiovascular, respiratory and other systems.
Depending on the spatial structure of all proteins can be divided into two large groups: fibrillar (they use nature as a structural material) and globular - enzymes, antibodies, some hormones, etc.
Enzymes , or enzymes act as catalysts in the body of fusion reactions (anabolic enzymes) and decay (catabolic enzymes).Enzymes have specificity of action, that is able to affect only the well-defined substrates. Many enzymes are required for the efficient operation of non-protein components called cofactors.During the digestive enzymes break down proteins to amino acids obtained, which are used by the body in the synthesis of other proteins or undergo decomposition to generate energy.
Many hormones are also proteins, polypeptides or amino acids.One of the most well-known protein hormone - insulin. The hormones in the body perform a regulatory function. For more information about the mechanism of action of hormones will be discussed in the section on the functions of the endocrine system.Blood protein - hemoglobin - carries the body transport function, there are protective proteins, receptor, and many other properties.In a separate group of release neuropeptides that are responsible for basic mental processes.
The structure of many proteins in addition to the peptide chain includes neaminokislotnye fragments . By this criterion, proteins are divided into simple, containing only the amino acid chain, and complex (proteids) containing neaminokislotnye fragments.
Complex proteins are divided into glycoproteins containing carbohydrate residues (this includes, in particular, immunoglobulins), lipoprotein associated with lipids, as well as metalloproteins, nucleoproteins, fosfoproteidy etc.
As part of this book on cholesterol, more of all these compounds, we consider only the lipoproteins - complexes of proteins with different fats. Proteins are composed of lipoproteins called apoprotein. On the types and functions of the lipoproteins , we'll talk later.
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