Protein - high-molecular organic compounds, built of radicals of amino acidsjoined together by peptide bonds; are the structural and functional basis of life. Mol. weight proteins several million. Proteins have different functions - structural, protective, enzymatic and hormonal, transport and, finally, osmotic. Proteins are enzymes (see), antibodies and antigens, many hormones (see) and other biologically active substances.
The basis of the structure of a protein is a polypeptide consisting of hundreds (tens) of amino acid residues located in the chain of the protein molecule in particular for each protein sequence. Under the influence of temperature, reducing agents, when changes in the environmental acidity proteins easily lose their native properties, denature.
Functional characteristics of proteins primarily depend on the sequence of amino acids (primary structure). Currently clarified the sequence of amino acids in the insulin, the hemoglobin, myoglobin and other proteins. There are fibrillar proteins (insoluble, mainly proteins stroma) and globular (soluble including the major part of biologically active proteins - see Albumins, Globulins). Some proteins known as fibrillar and in globular form (contractile protein actin). The composition of proteins are divided into two groups: simple proteins (actually proteins or proteins), consisting only of amino acids, and complex proteins ( proceedi), the molecular structure of which includes non-protein components. To complex proteins are lipoproteins, mukoproteidov (see), the nucleoprotein (see). Because proteins are free amino and carboxyl groups in the side chains, they are ampholytes (see Electrolytes), which determines their physico-chemical properties (buffering capacity, mobility in an electric field, solubility). On the solubility of proteins affected by the concentration of salts in solution, resulting protein mixture can be divided into fractions (i.e., groups of proteins that differ from each other molecular weight, solubility and other properties) with a sequential increase in the concentration of neutral salts. The separation of mixtures of proteins on protein fractions in the clinic is made also by the method of electrophoresis (see).
The metabolism of proteins - see Nitrogen metabolism.
Proteins in the diet. Sufficient high-quality proteins in the diet creates optimal conditions for the normal functioning of the organism, its growth, development and high availability. Quite a high level of protein in the nutrition of all age groups. Reduced levels of protein in the diet leads to a serious disturbance of body functions.
The main source of protein in the diet are foods of animal origin, some vegetable foods that contain a lot of protein. So, for example, 100 g of different products includes the following amounts of protein: in beef - 15,2-19 g, fish - 11,1 to 18.6 g, eggs - 10.6 g, milk (whole) - 2.8 g, cheese - 11,1 -13,6 g, cheese-20-22,6 g, bread- 5-10 g, cereals - 7-13 g, a bean - 23-24 g, soy beans) - 28,7 g, nuts - 4-23 g, potatoes - 2 g, vegetables, fruit - about 1,
The most valuable proteins, containing the whole complex of essential and nonessential amino acids (see), in optimal ratios are proteins of animal origin. Plant proteins less valuable because of the total lack of certain essential amino acids or their adverse ratio, but a number of vegetable protein (soy, rice, potatoes) by the ratio of amino acids close to the animal proteins.
Rational nutrition protein is created through the use in certain proportion of animal and plant proteins, amino acid composition of which are mutually complementary to each other. It is recommended to use more frequently in food products of animal origin (meat, fish) with vegetable side dishes, dishes from cereals and pasta products milk, fermented milk products, and so on
Plant proteins usually absorbed worse than animals. The absorption of protein depends and from a way of cooking food. The thermal processing of cheese, drying and baking of many products reduce the absorption contained proteins Grinding and cooking products of plant origin promote protein digestion.
The biological value of protein and amino acid uptake by the body increases with sufficient content of vitamins in the diet group (primarily pyridoxine and Pantothenic acid), as well as salts of magnesium, potassium, sodium. For a more complete use of proteins in the organism is necessary that the food was certain ratio of protein with other components, primarily with fats and carbohydrates (1:1 : 4). In the absence or insufficient content in the diet of carbohydrates or fats in the body is greatly strengthens the processes of the breakdown of proteins and the demand for them increases. Great influence on the use in the body of protein and has the power, in particular the intervals between meals. It is established that if too large intervals (10-12 hours). the absorption of protein is sharply reduced.
Sufficiency and usefulness of protein nutrition is Central to the maintenance of normal functioning of the body. In this regard, special importance is the determination of the optimum norms protein requirements. The human need for protein depends on many factors: gender, age, type of activity, conditions of life, climatic conditions, state of an organism. Taking into account the effect of various combinations of the above factors, daily allowance of protein for the adult population are 80-100 g or more, or no less than 1.0 to 1.5 grams of protein per 1 kg of weight. Due to the proteins it is recommended to provide an average of 14% of total calorie intake. Given that the need for protein is determined not only by their absolute number, but amino acid composition, it is recommended that animal proteins made 50-60% of the total number of proteins.
Proteins are widely used in clinical nutrition. The increased amount of protein is appointed if necessary, increase the reactivity of the organism. Indications to increase in the protein content in the diet are: depletion (when malnutrition sick a long time to get 120-150 g of protein daily), Hypo-and avitaminosis, anemia, rheumatism, faltering tuberculosis, peptic ulcer disease of the stomach, ulcerative colitis, etc. In some cases (for kidney, heart, expressed atherosclerosis, gout) protein intake should be limited. However, the amount of protein should not be less than 40-50 g / day in a long malobeloe diet. The limitations of the content of protein in the diet should not be at the expense of the most valuable proteins (milk products, eggs, meat).

Proteins; from the Greek. protos - first) - natural high-molecular compounds containing 50,6-54,5% of carbon, a 21.5-23.5% oxygen, 6.5 to 7.3%of hydrogen, 15-17,6% of nitrogen and 0,3-2,5% sulfur. Some (complex) B. also contain phosphorus, iron, copper, or other elements. During the hydrolysis B. decay to amino acids and therefore are polymers last. B. meet wherever found livelihoods; in each cell b is active mass of living matter. That is why even Engels defined the life as a form of existence of protein phone To B. include enzymes, causing a catalytic function, contractile patterns (for example, actomyosin muscles), performing the function of the movement, the antibodies produced in response to the introduction of alien substances and which have a protective effect, many hormones, supporting and structural education, etc.