Proteins are called nitrogenous macromolecular organic substances. They are built from amino acids. Proteins perform fundamental tasks in the life and structure of organisms, being their main and necessary component. It is thanks to these organic compounds that metabolism and energy transformations occur.
Due to the relatively large size of the molecules, the complexity of the structure, as well as the insufficient information on the structural composition of most substances, a rational unified classification of proteins has not been established. The existing separation system is largely arbitrary. During its construction, physical and chemical properties of proteins, sources of their production, biological activity, and other, often random, signs are taken as a basis.
So, globular and fibrillar, hydrophobic (insoluble) and hydrophilic (soluble) substances are isolated. This separation is based on the physicochemical properties of the compounds. Depending on the source of production, proteins of nervous tissue, blood serum, muscles and others are secreted. There are also bacterial, animal and plant compounds. In accordance with biological activity, hormone proteins, enzyme proteins, contractile and structural proteins, antibodies, and others are secreted. It should be noted that there are separate compounds that cannot be assigned to any of the above groups. This is due to the imperfection of the classification system and the exceptional diversity of the proteins themselves.
It is customary to divide the compounds into complex (proteids) and simple (proteins). Simple proteins are only amino acid polymers. Complex compounds, in addition to amino acid residues, contain non-protein inclusions.
In every cell there are thousands of organic macromolecular compounds. Due to the fact that during the life of the body these substances are destroyed sooner or later, the cell must carry out continuous protein synthesis to restore its organoids, membranes and other components. At the same time, a large number of cells carry out the formation of organic compounds for the whole organism. Such "production" is involved, for example, cells in the endocrine glands that produce hormones. Here, protein synthesis is most intense.
The development of compounds requires significant energy costs. ATP is a source providing not only protein synthesis, but also all cellular processes.
It should be noted that a variety of functions and tasks of the compounds is formed in accordance with their primary structure - the amino acid sequence in the molecule. Hereditary data on the primary protein structure are enclosed in the nucleotide chain of a DNA molecule. That section of deoxyribonucleic acid, which contains information about the amino acid sequence of one compound, is called the gene.
Protein synthesis occurs on ribosomes, in the cell cytoplasm. Information on the structure of the compound enters the cytoplasm from the nucleus in the form of i-RNA (messenger RNA). To carry out the synthesis of the i-RNA molecule, the DNA is unwound (despiralized). The subsequent process is based on the principle of complementarity. Using enzymes on one of the DNA chains, RNA molecules are synthesized.
The cytoplasm must necessarily contain a certain set of amino acids. It is necessary for the implementation of protein synthesis. The formation of these amino acids occurs due to the breakdown of food organic compounds. In addition, the amino acid can enter the site of direct synthesis (into the ribosome) by attaching to a special transport RNA (t-RNA).