Biochemistry is a branch of biology that studies the chemical composition of both individual cells and the whole organism. It is known that almost 98% of cellular contents include oxygen, carbon, nitrogen and hydrogen atoms. These chemical elements are called organogenic. 1.8% falls on potassium, sodium, magnesium, chlorine, phosphorus. In the human body, they are part of mineral s alts and have the form of simple or complex ions, ensuring the normal course of metabolic reactions. For example, the most important cell compounds responsible for the transmission of hereditary traits - nucleic acids - contain anions of acid residues of orthophosphoric acid.
Phosphorus-containing ions are also included in the ATP molecules, on which the provision of cells with energy depends. In this article, we will give examples that confirm the importantthe role of phosphorus in the human body and its effect on metabolism.
Covalent polar bonds and their meaning
The basis of the structure of organic substances that make up living matter is the ability of their molecules to form a certain type of chemical bond. It is called covalent polar and, arising between the atoms of non-metals, determines the main chemical characteristics of compounds. Biochemistry, studying the composition of the molecules of substances entering the cells of plants, fungi, animals, established their chemical composition. It turned out that, in addition to nitrogen, carbon, oxygen, they also include phosphorus. In the human body, it does not occur in a free state, as it is a highly toxic substance. Therefore, in living systems, the element has the form of meta-, ortho-, or pyrophosphoric acid anions, which have the ability to form bonds with metal cations. In what substances of the cell can they be found?
Phosphorus in complex organic molecules
Proteins of the skeletal system, hormones, vitamins and lipids form complex compounds with phosphorus-containing complex ions. In the human body there are complex compounds - phospholipids and phosphoproteins, which are part of the molecules of biologically active substances - enzymes and steroids. Covalent polar bonds in DNA and RNA nucleotides provide the formation of phosphodiester bonds in nucleic acid chains. Why is phosphorus needed in the human body and what are its functions in metabolism? Let's first consider this question at the cellular level of organization.
The place of phosphorus in the elemental composition of the cell
According to the content in the cytoplasm and organelles (0.2-1%), non-metal is in fourth place after organogenic elements. The most saturated with phosphorus compounds are the cells of the musculoskeletal system - osteocytes, the substance of dental tissue - dentin. Their content is high in neurons and neuroglia, which make up the nervous system. Phosphorus atoms are found in membrane proteins, nucleic acids and energy-intensive substances - ATP adenosine triphosphoric acid and in the reduced form of nicotinamide dinucleotide phosphate - NADP×H2. As you can see, in the human body, phosphorus is found in all vital structures: cells, tissues, physiological systems.
It is known that the level of homeostasis of a cell, which is an open biological system, depends on the concentration of various ions in the hyaloplasm and intercellular fluid. What is the function of phosphorus in maintaining the constancy of the internal environment of the human body?
Buffer system
Due to the property of semi-permeability through the outer membrane, various substances constantly enter the cell, a high concentration of which can adversely affect its vital activity. To neutralize the excess of toxic ions, the cytoplasm, together with sodium, potassium, calcium cations, contains acid residues of carbonate, sulfite and phosphoric acids. They are able to react with an excess of ions that have entered the cell and control the constancy of intracellular contents. The buffer system, in addition to ions of weak acids, necessarily includes anionsNRO42- and N2RO4 - containing phosphorus. In the human body, as part of the buffer system, it ensures the physiologically normal course of metabolic reactions at the cellular level.
Oxidative phosphorylation
The breakdown of organic compounds in a cell is called aerobic respiration. Its location is the mitochondria. Enzyme complexes are located on the inner folds - the cristae of organelles. For example, the ATP-ase system contains electron carrier molecules. Thanks to reactions catalyzed by enzymes, ATP is synthesized from ADP and free molecules of phosphoric acid - the universal energy substance of cells, which is spent on their reproduction, growth, and movement. Its formation can be represented as a simplified reaction scheme: ADP + F=ATP. Then adenosine triphosphoric acid molecules accumulate in the cytoplasm. They serve as a source of energy for performing mechanical work, for example, in the muscular system and in plastic exchange reactions. Consequently, phosphorus in the human body plays a leading role in energy metabolism.
Phosphodiester bonds of heredity molecules
A high content of atomic phosphorus is recorded in the cell nucleus, since the element is part of nucleic acids. Discovered back in the 19th century by the Swiss scientist F. Miescher, they are biopolymers and consist of monomers - nucleotides. Phosphorus presentboth in the purine and pyrimidine bases themselves, and in the bonds that form the RNA chains and the DNA supercoil. Nucleic acid monomers are capable of forming polymer structures due to the emergence of covalent bonds between the pentose and phosphoric acid residues of adjacent nucleotides. They are called phosphodiesters. The destruction of DNA and RNA molecules that occurs in human cells under the influence of hard gamma radiation or as a result of poisoning with toxic substances occurs due to the breaking of phosphodiester bonds. It causes cells to die.
Biological membranes
Structures that limit the internal contents of the cell also contain phosphorus. In the human body, up to 40% of dry body weight falls on compounds containing phospholipids and phosphoproteins. They are the main components of the membrane layer, which also contains substances such as proteins and carbohydrates. A high content of phosphorus is characteristic of the membranes of neurocytes and their processes - dendrites and axons. Phospholipids give membranes plasticity, and due to the presence of cholesterol molecules, also strength. They also play the role of second messengers - signal molecules that are activators of effector proteins involved in the conduction of a nerve impulse.
Parathyroid glands and their role in phosphorus metabolism
Resembling peas, lying on both lobes of the thyroid gland and weighing 0.5-0.8 g each, the parathyroid glands secrete parathyroid hormone. It regulates the exchange of elements such ascalcium and phosphorus in the human body. Their functions are to act on osteocytes and osteoblasts - cells of the skeletal system, which, under the influence of the hormone, begin to release s alts of phosphoric acid into the extracellular fluid. With hyperfunction of the parathyroid glands, human bones lose strength, soften and collapse, the phosphorus content in them drops sharply. At this time, the risk of fractures of the spine, pelvic bones and hips, which threaten the life of the patient, increases. At the same time, the amount of calcium increases. This leads to hypercalcemia with symptoms of peripheral nerve damage and a drop in skeletal muscle tone. Parathyroid hormone also acts on the kidneys, reducing the reabsorption of phosphorus s alts from the primary urine. An increase in phosphate in the tissues of the kidneys causes hyperphosphaturia and the formation of stones.
Bone mineral composition
The hardness, strength and elasticity of the support system depends on the chemical composition of bone tissue cells. Osteocytes contain both organic compounds, such as the protein ossein, and inorganic substances containing calcium and magnesium phosphate s alts. As a person ages, the amount of mineral components, such as hydroxylapatites, in osteocytes and osteoblasts increases. Abnormal mineralization of bone tissue, the accumulation of calcium s alts and excess phosphorus in the human body lead to a loss of elasticity and strength of all parts of the skeleton, so older people are more likely to be at risk of injuries and fractures.
Transformation of phosphorus compounds in the bodyhuman
The largest digestive gland in the human body - the liver - plays a leading role in the metabolism of phosphorus-containing substances. Parathyroid hormones and vitamin D also influence these processes. The daily requirement of the element for adults is 1.0-2.0 grams, for children and adolescents - up to 2.5 g. Phosphorus in the form of easily digestible s alts, as well as in complexes with proteins and carbohydrates, enters the human body with food.
Sunflower, pumpkin, hemp seeds are saturated with it. There is a lot of phosphorus in animal products in chicken liver, beef, hard cheeses, and fish. An excess of phosphorus in the body can occur as a result of a violation of the reabsorption function of the kidneys, improper use of vitamins, and a lack of calcium in food. The negative effect of phosphorus on the human body is manifested primarily in the damage to the cardiovascular system, kidneys and bone apparatus and may indicate serious metabolic disorders.
