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The main nitrogen-containing substances of which proteins consist, are amino acids. The amount of amino acids is small - them only 2 All enormous variety of the proteins containing in the nature is known represents various combination of known amino acids. Properties and qualities of proteins depend on their combination.

The first concept of a structure of proteins belongs to the Dutch chemist Mr. Mulder (18 based on the theory of radicals, he formulated concept about the minimum structural unit which is a part of all proteins. Mulder called this unit a protein (, and the concept - the theory of a protein. Later the structure of a protein was specified; in addition to proteinny units some proteins contained sulfur and phosphorus. G. Mulder's works promoted a wide circulation of views about unity of all proteins, their fundamental value in the world of wildlife.

All proteins can be divided into simple proteins, or proteins, and difficult proteins, or proteida (complexes of proteins with not proteinaceous connections). Simple proteins (they are widespread in animal and vegetable the world are polymers only of amino acids; difficult, besides the remains of amino acids, contain also not proteinaceous, so-called prostetichesky groups.

But nutrients in that look in what they are eaten, cannot be soaked up and be used by an organism. Only water, mineral salts and vitamins are soaked up and acquired in that look in what they arrive. Other nutrients in a digestive tract are exposed both to physical impacts (are crushed and fray), and to chemical changes which happen under the influence of special substances - the enzymes containing in juice of digestive glands. Under the influence of digestive juice nutrients are split on simpler which are soaked up and acquired by an organism.

Proteinoida. Proteins of basic fabrics (bone, cartilage, sheaves, sinews, nails, hair). Insoluble or difficult soluble in water, salt and aqueous-alcoholic mixes of a squirrel with the high content of sulfur. The keratin, collagen, fibroin belong to proteinoida.

Albumine. Low molecular weight (15-17 thousand). Sour properties are characteristic. Rastvorima in water, and weak salt solutions. Are besieged by neutral salts at 100% saturation. Participate in maintenance of osmotic pressure of blood, transport various substances with blood. Contain in blood serum, milk, egg white.

Because of rather big sizes of proteinaceous molecules, complexity of their structure and absence enough exact data on structure of the majority of proteins still are not present rational chemical classification of proteins. The existing classification considerably is conditional and constructed mainly on the basis of physical and chemical properties of proteins, sources of their receiving, biological activity and others, quite often casual, signs. So, on physical and chemical properties of a squirrel divide on fibrillyarny and globulyarny, on hydrophilic (rastvorima and hydrophobic (are insoluble, etc. On a source of receiving a squirrel subdivide on animal, vegetable and bacterial; on muscle proteins, nervous fabric, blood serum, etc.; on biological activity – on proteins-enzymes, proteins hormones, structural proteins, sokratitelny proteins, antibodies, etc. It must be kept in mind, however, that because of imperfection of the classification, and also owing to exclusive variety of proteins many of separate proteins cannot be carried to one of the groups described here.

Glyutelina. The vegetable proteins containing in a gluten of seeds cereal and some other in green parts of plants. Rastvorima in weak solutions of alkalis are insoluble in water, solutions of salts and ethanol, but well. Contain all irreplaceable amino acids, are full-fledged food.

Histones. Have rather low molecular weight (12-13 thousand), with prevalence of alkaline properties. Are localized generally in kernels of cages. Rastvorima in weak acids, are besieged by ammonia and alcohol. Have only tertiary structure. Are under natural conditions strongly connected with DNA and are a part of nucleoproteids. The main function — regulation of transfer of genetic information with DNA and RNA (transfer blocking is possible).