At the end of the 19th century, the industry was formedbiology, called biochemistry. She studies the chemical composition of a living cell. The main task of science is the cognition of the peculiarities of the metabolism and energy regulating the vital activity of plant and animal cells.
The concept of the chemical composition of cells
As a result of careful research, scientiststhe chemical organization of cells has been studied and it has been established that living beings have more than 85 chemical elements in their composition. And some of them are mandatory for almost all organisms, while others are specific and occur in specific biological species. A third group of chemical elements is present in cells of microorganisms, plants and animals in fairly small quantities. Chemical elements in the composition of cells are most often in the form of cations and anions, from which mineral salts and water are formed, and carbon-containing organic compounds are synthesized: carbohydrates, proteins, lipids.
Organogenic elements
In biochemistry, they include carbon, hydrogen,oxigen and nitrogen. Their totality is in the cell from 88 to 97% of the other chemical elements in it. Especially important is the carbon. All organic substances in the cell consist of molecules containing carbon atoms in their composition. They are able to connect to each other, forming chains (branched and unbranched), as well as cycles. This ability of carbon atoms underlies the striking variety of organic substances that make up the cytoplasm and cellular organelles.
For example, the inner contents of a cell consist ofsoluble oligosaccharides, hydrophilic proteins, lipids, various types of ribonucleic acid: transport RNA, ribosomal RNA and information RNA, as well as free monomers - nucleotides. A similar chemical composition has a cellular nucleus. It also contains molecules of deoxyribonucleic acid, which are part of the chromosomes. All of the above compounds have in their composition the atoms of nitrogen, carbon, oxygen, hydrogen. This is proof of their particularly important importance, since the chemical organization of cells depends on the content of organogenic elements that make up the cellular structures: hyaloplasm and organelles.
Macro elements and their meanings
Chemical elements, which are also very commonare found in the cells of various species of organisms, in biochemistry they are called macroelements. Their content in the cell is 1.2% - 1.9%. The macroelements of the cell include: phosphorus, potassium, chlorine, sulfur, magnesium, calcium, iron and sodium. All of them perform important functions and are part of various cellular organelles. So, the ferrous ion is present in the blood protein - hemoglobin, which transports oxygen (in this case it is called oxyhemoglobin), carbon dioxide (carbogemoglobin) or carbon monoxide (carboxyhemoglobin).
Sodium ions provide the most important formintercellular transport: the so-called sodium-potassium pump. They are also part of interstitial fluid and blood plasma. Magnesium ions are present in the molecules of chlorophyll (photopigment of higher plants) and participate in the process of photosynthesis, as they form reaction centers that capture photons of light energy.
Calcium ions provide nerveimpulses along fibers, and also are the main component of osteocytes - bone cells. Calcium compounds are widely distributed in the world of invertebrates, in which the shells are composed of calcium carbonate.
Chlorine ions participate in the recharging of cell membranes and provide the appearance of electrical impulses that underlie nervous excitation.
Sulfur atoms are a part of native proteins and cause their tertiary structure, "stitching" the polypeptide chain, resulting in the formation of a globular protein molecule.
Potassium ions are involved in the transport of substances throughcell membranes. Phosphorus atoms are part of such an important energy-intensive substance as adenosine triphosphate, and are also an important component of the molecules of deoxyribonucleic and ribonucleic acids, which are the main substances of cellular heredity.
Functions of trace elements in cellular metabolism
About 50 chemical elements constituting less0.1% in the cells are called micronutrients. These include zinc, molybdenum, iodine, copper, cobalt, fluorine. With a small content, they perform very important functions, as they are part of many biologically active substances.
For example, zinc atoms are in moleculesinsulin (a pancreatic hormone that regulates blood glucose), iodine is an integral part of thyroid hormones, thyroxine and triiodothyronine, which control the level of metabolism in the body. Copper, along with iron ions, is involved in blood formation (the formation of red blood cells, platelets and leukocytes in the red bone marrow of vertebrates). Copper ions are part of the hemocyanin pigment present in the blood of invertebrates, such as mollusks. Therefore, their hemolymph color is blue.
Even less content in the cell of such chemicalelements like lead, gold, bromine, silver. They are called ultramicrocells and are part of plant and animal cells. For example, in corn kernels, gold ions were detected by chemical analysis. Bromine atoms in large quantities are part of the cells of the thallus of brown and red algae, such as sargassuma, kelp, fucus.
All previous examples and facts explainhow the chemical composition, function and structure of the cell are interrelated. The table below shows the content of various chemical elements in the cells of living organisms.
General characteristics of organic substances
Chemical properties of cells of various groupsorganisms depend in a certain way on carbon atoms, which account for more than 50% of the cell mass. Almost all the dry matter of the cell is represented by carbohydrates, proteins, nucleic acids and lipids, which have a complex structure and a large molecular weight. Such molecules are called macromolecules (polymers) and consist of simpler elements - monomers. Protein substances play an extremely important role and perform many functions, which will be discussed below.
The role of proteins in the cell
Biochemical analysis of living compoundscell, confirms the high content of organic substances such as proteins. This fact is a logical explanation: proteins perform various functions and participate in all manifestations of cellular activity.
Например, защитная функция белков заключается в the formation of antibodies - immunoglobulins produced by lymphocytes. Protective proteins such as thrombin, fibrin and thromboblastin, provide blood clotting and prevent its loss in injuries and wounds. The cell contains complex cell membrane proteins that have the ability to recognize foreign compounds - antigens. They change their configuration and tell the cell about the potential hazard (signaling function).
Some proteins perform a regulatory function andare hormones, such as oxytocin, produced by the hypothalamus, is reserved by the pituitary gland. When it enters the bloodstream, oxytocin acts on the muscle walls of the uterus, causing it to contract. Vasopressin protein also has a regulatory function, controlling blood pressure.
In muscle cells are actin and myosin,able to contract, which causes the motor function of muscle tissue. Trophic function is also characteristic of proteins, for example, albumin is used by the embryo as a nutrient for its development. Blood proteins of various organisms, such as hemoglobin and hemocyanin, carry oxygen molecules - perform the transport function. If more energy-intensive substances, such as carbohydrates and lipids, are fully utilized, the cell proceeds to the breakdown of proteins. One gram of this substance gives 17, 2 kJ of energy. One of the most important functions of proteins is catalytic (proteins-enzymes accelerate chemical reactions occurring in the compartments of the cytoplasm). Based on the above, we have seen that proteins perform many very important functions and are necessarily part of the animal cell.
Biosynthesis of protein
Consider the process of protein synthesis in the cell,which occurs in the cytoplasm using organelles such as ribosomes. Due to the activity of special enzymes, with the participation of calcium ions, the ribosomes are combined into polysomes. The main functions of the ribosomes in the cell are the synthesis of protein molecules, starting from the process of transcription. As a result, mRNA molecules are synthesized, to which the polysomes join. Then the second process begins - translation. Transport RNAs combine with twenty different types of amino acids and bring them to polysomes, and since the functions of the ribosomes in the cell are the synthesis of polypeptides, these organelles form complexes with tRNA, and the amino acid molecules bind with each other by peptide bonds to form a protein macromolecule.
The role of water in metabolism
Цитологические исследования подтвердили тот факт, that the cell, the structure and composition of which we study, on average 70% consists of water, and in many animals that lead to aquatic life (for example, intestinal cavities), its content reaches 97-98%. With this in mind, the chemical organization of cells includes hydrophilic (capable of dissolving) and hydrophobic (water repellent) substances. Being a universal polar solvent, water plays an exceptional role and directly affects not only functions, but also the very structure of the cell. The table below shows the water content in cells of various types of living organisms.
Carbohydrate function in the cell
As we found out earlier, to important organicsubstances - polymers - are also carbohydrates. These include polysaccharides, oligosaccharides and monosaccharides. Carbohydrates are part of more complex complexes - glycolipids and glycoproteins, which make up cell membranes and supramembrane structures, such as glycocalyx.
In addition to carbon, carbohydrates include atoms.oxygen and hydrogen, and some polysaccharides also contain nitrogen, sulfur and phosphorus. There are many carbohydrates in plant cells: potato tubers contain up to 90% starch, carbohydrates content in seeds and fruits up to 70%, and in animal cells they are found in the form of compounds such as glycogen, chitin and trehalose.
Simple sugars (monosaccharides) have the general formulaCnH2nOn and are divided into tetroses, triose, pentose and hexose. The latter two are most common in the cells of living organisms, for example, ribose and deoxyribose are part of nucleic acids, and glucose and fructose participate in assimilation and dissimilation reactions. Oligosaccharides are often found in plant cells: sucrose is stored in cells of sugar beet and sugar cane, maltose is found in germinated seeds of rye and barley.
Disaccharides have a sweetish taste and a gooddissolve in water. Polysaccharides, being biopolymers, are represented mainly by starch, cellulose, glycogen, and laminarin. Chitin belongs to the structural forms of polysaccharides. The main function of carbohydrates in the cell - energy. As a result of hydrolysis and energy metabolism reactions, polysaccharides are broken down to glucose, and then it is oxidized to carbon dioxide and water. As a result, one gram of glucose releases 17.6 kJ of energy, and the starch and glycogen stores are, in essence, a reservoir of cellular energy.
Glycogen is deposited mainly in muscletissues and liver cells, plant starch in tubers, bulbs, roots, seeds, and in arthropods such as spiders, insects, and crustaceans, trehalose oligosaccharide plays a major role in energy supply.
Carbohydrates are different from lipids and proteins.ability to oxygen-free splitting. This is extremely important for organisms living in conditions of deficiency or lack of oxygen, for example, for anaerobic bacteria and helminths - human and animal parasites.
There is another function of carbohydrates in the cell -construction (structural). It lies in the fact that these substances are the supporting structures of cells. For example, cellulose is part of the cell walls of plants, chitin forms the outer skeleton of many invertebrates and is found in fungal cells, the olysaccharides together with lipid and protein molecules form glycocalyx, a supermembrane complex. It provides adhesion - clumping of animal cells between themselves, leading to the formation of tissues.
Lipids: structure and function
These organic substances arehydrophobic (insoluble in water) can be extracted, i.e. extracted from cells using non-polar solvents such as acetone or chloroform. The function of lipids in a cell depends on which of the three groups they belong to: fats, waxes, or steroids. Fats are most common in all cell types.
Animals accumulate them in the subcutaneous adipose.In tissue, nerve tissue contains fat in the form of myelin sheaths of nerves. It also accumulates in the kidneys, liver, and insects in the fat body. Liquid fats - oils - are found in the seeds of many plants: cedar, peanuts, sunflower, olives. The content of lipids in cells varies from 5 to 90% (in adipose tissue).
Steroids and waxes are different from fats in that theyThey do not have fatty acid residues in their composition. So, steroids are hormones of the cortical layer of the adrenal glands that affect the puberty of the body and are components of testosterone. They are also found in vitamins (for example, vitamin D).
The main functions of cell lipids areenergy, construction and protection. The first is due to the fact that 1 gram of fat gives 38.9 kJ of energy during splitting - much more than other organic substances - proteins and carbohydrates. In addition, the oxidation of 1g of fat releases almost 1.1 grams. water. That is why some animals with a reserve of fat in their bodies can be without water for a long time. For example, gophers may hibernate for more than two months without needing water, and the camel does not drink water when crossing the desert for 10–12 days.
The building function of lipids is tothat they are an integral part of the cell membrane, and are also part of the nerves. The protective function of lipids is that the layer of fat under the skin around the kidneys and other internal organs protects them from mechanical injury. The specific heat-insulating function is inherent in animals that have been in the water for a long time: whales, seals, and fur seals. A thick subcutaneous fat layer, for example, in a blue whale is 0.5 m, it protects the animal from hypothermia.
The value of oxygen in cellular metabolism
Aerobic organisms to whichthe vast majority of animals, plants and humans, use atmospheric oxygen for energy metabolism reactions, leading to the splitting of organic substances and the release of a certain amount of energy accumulated in the form of adenosine triphosphate acid molecules.
So, with full oxidation of one mole of glucose,2800 kJ of energy is released on the cristae of mitochondria, of which 1596 kJ (55%) is stored in the form of ATP molecules containing macroergic bonds. Thus, the main function of oxygen in the cell is the implementation of aerobic respiration, which is based on a group of enzymatic reactions of the so-called respiratory chain, occurring in cellular organelles - mitochondria. In prokaryotic organisms - phototrophic bacteria and cyanobacteria - the oxidation of nutrients occurs under the action of oxygen, diffusing into the cells on the internal outgrowths of the plasma membranes.
We have studied the chemical organization of cells, as well as the processes of protein biosynthesis and the function of oxygen in cellular energy metabolism.
