Chemical organization of cells: organic substances, macro- and microelements

At the end of the 19th century, a branch of biology was formed, 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 that regulate the vital activity of plant and animal cells.

The concept of the chemical composition of cells

As a result of careful research, scientists have studied the chemical organization of cells and found 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. And the third group of chemical elements is present in cells of microorganisms, plants and animals in small enough 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 also carbon-containing organic compounds are synthesized: carbohydrates, proteins, lipids.

Organogenic elements

In biochemistry, they include carbon, hydrogen, oxygen and nitrogen. Their totality is in the cell from 88 to 97% of the other chemical elements that are 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 internal contents of a cell consist of soluble 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 cell 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: the hyaloplasm and the organelles.

Macro elements and their meanings

Chemical elements, which are also very often found in the cells of various species of organisms, are called macrocells in biochemistry. 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 type of intercellular transport: the so-called sodium-potassium pump. They are also part of interstitial fluid and blood plasma. Magnesium ions are present in chlorophyll molecules (photopigment of higher plants) and participate in the process of photosynthesis, since they form reaction centers that capture photons of light energy.

Calcium ions provide nerve impulses along the fibers, and are also 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 part of the native proteins and cause their tertiary structure, "stitching" the polypeptide chain, resulting in the formation of a globular protein molecule.

Potassium ions participate in the transport of substances through cell membranes. Atoms of phosphorus are a part of such an important energy-intensive substance as adenosine triphosphoric acid, and also an important component of the molecules of deoxyribonucleic and ribonucleic acids, which are the main substances of cellular heredity.

Functions of microelements in cellular metabolism

About 50 chemical elements, which make up less than 0.1% in cells, are called microelements. These include zinc, molybdenum, iodine, copper, cobalt, fluorine. With insignificant content, they perform very important functions, as they are part of many biologically active substances.

For example, zinc atoms are found in insulin molecules (the hormone of the pancreas regulating blood glucose level), iodine is an integral part of the thyroid hormones - thyroxine and triiodothyronine, which control the level of metabolism in the body. Copper, along with iron ions, participates in hematopoiesis (the formation of erythrocytes, platelets and leukocytes in the red bone marrow of vertebrates). Copper ions are part of the pigment of hemocyanin present in the blood of invertebrates, for example mollusks. Therefore, the color of hemolymph they have blue.

Even less is the content in the cell of such chemical elements as lead, gold, bromine, silver. They are called ultramicroelements and are part of plant and animal cells. For example, in the grains of corn, gold ions were detected by chemical analysis. Atoms of bromine in a large number are included in the composition of thallus cells of brown and red algae, for example sargassum, kelp, fucus.

All the above examples and facts explain how the chemical composition, functions 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

The chemical properties of cells of different groups of organisms depend in a certain way on the carbon atoms, the proportion of which is more than 50% of the cell mass. Practically 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 compounds entering into a living cell confirms the high content of organic substances such as proteins in it. This fact has a logical explanation: proteins perform a variety of functions and participate in all manifestations of cellular life.

For example, the protective function of proteins is the formation of antibodies - immunoglobulins, produced by lymphocytes. Such protective proteins, like thrombin, fibrin and thromboblastin, provide blood clotting and prevent its loss in injuries and injuries. The cell consists of complex proteins of cell membranes, which have the ability to recognize foreign compounds - antigens. They change their configuration and inform the cell of potential danger (signal function).

Some proteins perform a regulatory function and are hormones, for example, oxytocin, produced by the hypothalamus, is reserved by the pituitary gland. Entering into the blood, oxytocin affects the muscular walls of the uterus, causing it to contract. Protein vasopressin also performs a regulatory function, controlling blood pressure.

In the muscle cells are actin and myosin, able to contract, which causes the motor function of muscle tissue. For proteins, trophic function is also characteristic, for example, albumin is used by the embryo as a nutrient for its development. Blood proteins of various organisms, for example hemoglobin and hemocyanin, carry oxygen molecules - perform a transport function. If more energy-intensive substances, such as carbohydrates and lipids, are fully used, the cell begins to break down the proteins. One gram of this substance gives 17, 2 kJ of energy. One of the most important functions of proteins is catalytic (protein-enzymes accelerate chemical reactions that occur in the compartment of the cytoplasm). Based on the foregoing, we were convinced 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 a cell that occurs in the cytoplasm with the help of organelles such as ribosomes. Thanks to the activity of special enzymes, with the participation of calcium ions, the ribosomes combine into polysomes. The main functions of ribosomes in a cell are the synthesis of protein molecules, which starts with the process of transcription. As a result, it synthesizes mRNA molecules, to which polysomes are attached. Then the second process begins - translation. Transport RNAs combine with twenty different kinds 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 are linked together by peptide bonds to form the protein macromolecule.

The role of water in metabolic processes

Cytological studies have confirmed the fact that the cell, the structure and composition of which we study, is on average 70% water, and in many animals that lead the aquatic life (for example, coelenterates), its content reaches 97-98%. With this in mind, the chemical organization of cells includes hydrophilic (soluble) and hydrophobic (water-repellent) substances. Being a universal polar solvent, water plays an exceptional role and directly affects not only the functions, but also the very structure of the cell. The table below shows the water content in the cells of various types of living organisms.

Function of carbohydrates in a cage

As we found out earlier, important carbohydrates are important organic substances - polymers. These include polysaccharides, oligosaccharides and monosaccharides. Carbohydrates are part of more complex complexes - glycolipids and glycoproteins, of which cell membranes and supramembrane structures, for example glycocalyx, are built.

In addition to carbon, carbohydrates include oxygen and hydrogen atoms, and some polysaccharides also contain nitrogen, sulfur and phosphorus. There are many carbohydrate plant cells: potato tubers contain up to 90% starch, in seeds and fruits carbohydrates up to 70%, and in animal cells they occur in the form of compounds such as glycogen, chitin and trehalose.

Simple sugars (monosaccharides) have the general formula CnH2nOn and are divided into tetroses, trioses, pentoses and hexoses. The latter two are most common in cells of living organisms, for example, ribose and deoxyribose are part of nucleic acids, and glucose and fructose are involved 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 contained in germinated grains of rye and barley.

Disaccharides have a sweetish taste and are readily soluble 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 is energy. As a result of hydrolysis and reactions of energy metabolism, polysaccharides split up to glucose, and it is then oxidized to carbon dioxide and water. As a result, one gram of glucose releases 17.6 kJ of energy, and stocks of starch and glycogen, in fact, are a reservoir of cellular energy.

Glycogen is deposited mainly in muscle tissue and liver cells, vegetable starch in tubers, onions, root crops, seeds, and in arthropods, for example spiders, insects and crustaceans, the main role in energy supply is played by trehalose oligosaccharide.

Carbohydrates differ from lipids and proteins by the ability to oxygen-free digestion. 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 - building (structural). It consists in the fact that these substances are the supporting structures of cells. For example, cellulose is a part of cell walls of plants, chitin forms the outer skeleton of many invertebrates and occurs in fungal cells, olisaccharides together with lipid and protein molecules form a glycocalyx-supramembrane complex. It provides adhesion - clumping of animal cells among themselves, leading to the formation of tissues.

Lipids: structure and function

These organic substances that are hydrophobic (water-insoluble) can be recovered, that is, extracted from the cells by non-polar solvents such as acetone or chloroform. The functions of lipids in a cell depend on which of the three groups they belong to: fats, waxes or steroids. Fats are most widely distributed in all types of cells.

Animals accumulate them in subcutaneous adipose tissue, the nerve tissue contains fat in the form of myelin sheaths of nerves. It also accumulates in the kidneys, liver, in insects - in the fatty body. Liquid fats - oils - are found in the seeds of many plants: cedar, peanuts, sunflower, olives. The lipid content in cells varies from 5 to 90% (in adipose tissue).

Steroids and waxes differ from fats in that they do not have fatty acid residues in the molecules. Thus, steroids are the hormones of the cortical layer of the adrenals, which affect the sexual maturation of the body and are components of testosterone. They are also part of vitamins (for example, vitamin D).

The main functions of lipids in the cell are energy, building and protective. The first is due to the fact that 1 gram of fat during the cleavage yields 38.9 kJ energy - much more than other organic substances - proteins and carbohydrates. In addition, when oxidizing 1g of fat, almost 1.1 gr is released. water. That's why some animals having a store of fat in their body can stay without water for a long time. For example, gophers can sleep more than two months without needing water, and a camel does not drink water during transitions through the desert for 10-12 days.

The building function of lipids is that they are an integral part of cell membranes, and also form part of the nerves. The protective function of lipids is that a layer of fat under the skin around the kidneys and other internal organs protects them from mechanical injuries. A specific thermal insulation function is inherent in animals that have been in the water for a long time: whales, seals, seals. A thick subcutaneous fat layer, for example, in a blue whale is 0.5 m, it protects the animal from hypothermia.

The importance of oxygen in cellular metabolism

Aerobic organisms, which include the 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 molecules of adenosine triphosphate.

Thus, with the complete oxidation of one mole of glucose occurring on the mitochondrial crystals, 2800 kJ of energy is released, 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 that occur in cellular organelles - mitochondria. In prokaryotic organisms - phototrophic bacteria and cyanobacteria - the oxidation of nutrients occurs under the influence of oxygen, diffusing into cells into internal outgrowths of plasma membranes.

We have studied the chemical organization of cells, and also examined the processes of protein biosynthesis and the function of oxygen in cellular energy metabolism.