Protein in nutrition?

Proteins are, from the chemical point of view, natural macromolecular compounds, with the structure of polypeptides, which form-amino acids by hydrolysis. They contain besides carbon, hydrogen, oxygen, nitrogen, sulfur, potassium, and other halogens. Some hormone containing proteins, they having the role of regulating the activity of the body. They patricipates at formation of antibody, helping to rid of toxins and microbes. Formation of enzymes and yeast requires presence of proteins. And last but not least, they participate in the formation of carbon dioxide, water, by the energy intake resulted from their combustion.
Daily diet contains a mixture of amino acids. From this mixture, most amino acids can be synthesized by the body, but 8 of them can be introduced into the body only through food. Through food,   into the body are introduced proteins that come from 2 sources: crop and animal.Those of animal origin (meat, milk, eggs), which are indispensable to a rational nutrition, have the advantage that are rich in protein, but the disadvantage that they are expensive, are made with a high consumption of plant products and are deficient in quantitatively terms .Those of vegetable origin (cereals, oilseeds and pulses), are the cheapest, so available, in the most large quantity, for the earth'  population.Some vegetable proteins can successfully replace animal protein, e.g. egg protein can be substituted for soy. Plant seed oil, also give high percentage of proteins: sunflower, groundnuts, cotton. Biological value  represents the  percentage of nitrogen kept by the body.It is determined by the presence or absence of certain amino acids in certain proportions, in the protein. After the biological value, we can classify the proteins in food:
-complete protein, containing all essential amino acids (lysine, methionine, isoleucine, tryptophan), needed to maintain protein balance of body  in optimal proportions for the synthesis of body protein balance. In the normal quantity, they maintain growth. Eg milk, cheese, eggs, meat . -partially

- complex protein, which also contain all the essential amino acids (lysine, methionine, isoleucine, tryptophan), but not in optimal scale for synthesis of body protein balance. To maintain body growth, we need a double intake of complete protein. Ex: wheat, rice, oats, some dried legumes.