Biochemistry

A hydrogen cation or proton (iff) plays an extremely important role in biological processes. Its concentration in solutions determines their acidic properties and is an important characteristic of any biological medium. Hydrogen plays an important role in the formation of special bonds in bioorganic molecules called hydrogen bonds. Under certain conditions, a hydrogen atom is capable of connecting not with one, but simultaneously with two other atoms. However, a strong (covalent) bond is formed only with one of them, while a less strong, non- covalent bond is formed with the other. This non-covalent bond is called the hydrogen bond, and it is customary to depict the dotted line. Hydrogen bonds determine, for example, the secondary and tertiary structure of proteins, the structure of plant (cellulosic) fibers, the stability of the DNA double helix, the course of key biological processes such as transcription and translation of genetic information. Phosphorus is quite common in nature. It accounts for 8-10' 2 % of the total mass of the earth's crust, which corresponds to 15 billion tons. This amount of phosphorus essentially limits the scale of life on Earth. The biological role of phosphorus is quite diverse. This element is part of cell membranes, nucleic acids and ATP, is involved in the metabolism of carbohydrates, in the formation of bone tissue and the blood buffer system. An adult's body contains about 4.5 kg of phosphorus. The most significant role in biological systems is played by salts of phosphoric acid (H } PO 4 ) - phosphates. So, soluble potassium phosphates (K 2 HPO 4 , KH2PO4) form a phosphate buffer system responsible for the constant pH of the intracellular fluid. Difficultly soluble calcium salts of phosphoric acid, for example, hydroxyapatite 3Ca 3 (PO 4 )2 • Ca(OH) 2 and others form the mineral base of the bone tissue of vertebrates and humans, and tooth enamel contains fluoroapatite Са 5 Ғ(РО 4 ) 3 , insoluble in acids. That is why toothpaste containing fluorine compounds is used to restore tooth enamel. Among the organic compounds of phosphorus, the most important and widely represented in biological systems are esters of phosphoric acid, which are called alkylphosphates. These compounds are formed by the binding of phosphoric acid to organic molecules, and the process of their formation is called phosphorylation. The remainder of phosphoric acid is part of many derivatives of carbohydrates, proteins and lipids, as well as all nucleic acids. For bioenergy, the widely known adenosinetriphosphoric acid, or ATP for short, is of particular importance. Its formation in the process of biological oxidation is called oxidative phosphorylation, or phosphorylation associated with electron transport. 9