At the end of the 19th century, a branch of biology called biochemistry was formed. It studies the chemical composition of a living cell. The main task of science is to understand the characteristics of metabolism and energy that regulate the vital activity of plant and animal cells.
The concept of the chemical composition of the cell
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. Moreover, some of them are obligatory for almost all organisms, while others are specific and are found in specific biological species. And the third group of chemical elements is present in the cells of microorganisms, plants and animals in fairly small quantities. Cells contain chemical elements most often in the form of cations and anions, from which mineral s alts and water are formed, and carbon-containing organic compounds are synthesized: carbohydrates, proteins, lipids.
Organogenic elements
In biochemistry these include carbon, hydrogen,oxygen and nitrogen. Their totality in the cell is from 88 to 97% of the other chemical elements in it. Carbon is especially important. All organic substances in the composition of the cell are composed of molecules containing carbon atoms in their composition. They are able to connect with each other, forming chains (branched and unbranched), as well as cycles. This ability of carbon atoms underlies the amazing variety of organic substances that make up the cytoplasm and cellular organelles.
For example, the internal content of a cell consists of soluble oligosaccharides, hydrophilic proteins, lipids, various types of ribonucleic acid: transfer RNA, ribosomal RNA and messenger RNA, as well as free monomers - nucleotides. The cell nucleus has a similar chemical composition. It also contains deoxyribonucleic acid molecules that are part of the chromosomes. All of the above compounds contain atoms of nitrogen, carbon, oxygen, hydrogen. This is proof of their particularly important significance, since the chemical organization of cells depends on the content of organogenic elements that make up cellular structures: hyaloplasm and organelles.
Macro elements and their meanings
Chemical elements, which are also very common in the cells of various types of organisms, are called macronutrients 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 variouscell organelles. So, the ferrous ion is present in the blood protein - hemoglobin, which transports oxygen (in this case it is called oxyhemoglobin), carbon dioxide (carbohemoglobin) 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 the interstitial fluid and blood plasma. Magnesium ions are present in chlorophyll molecules (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 the conduction of 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, whose shells are composed of calcium carbonate.
Chlorine ions are involved in the recharging of cell membranes and provide the occurrence of electrical impulses that underlie nervous excitation.
Sulfur atoms are part of native proteins and determine their tertiary structure by "crosslinking" the polypeptide chain, resulting in the formation of a globular protein molecule.
Potassium ions are involved in the transport of substances across cell membranes. Phosphorus atoms are part of such an important energy-intensive substance as adenosine triphosphoric acid, and are also an important component of deoxyribonucleic and ribonucleic acid molecules, which are the main substances of cellular heredity.
Functions of trace elements in the cellularmetabolism
About 50 chemical elements that make up less than 0.1% in cells are called trace elements. These include zinc, molybdenum, iodine, copper, cob alt, fluorine. With an insignificant content, they perform very important functions, as they are part of many biologically active substances.
For example, zinc atoms are found in the molecules of insulin (a pancreatic hormone that regulates blood glucose levels), 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, is involved in hematopoiesis (the formation of erythrocytes, 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 molluscs. Therefore, the color of their hemolymph is blue.
Even less 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, gold ions were detected in corn kernels by chemical analysis. Bromine atoms in large quantities are part of the cells of the thallus of brown and red algae, such as sargassum, kelp, fucus.
All the above examples and facts explain how the chemical composition, functions and structure of the cell are interconnected. 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 groups of organisms in a certain way depend on carbon atoms, the proportion of which is more than 50% of the cell mass. Almost all dry matter of the cell is represented by carbohydrates, proteins, nucleic acids and lipids, which have a complex structure and 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 the compounds that make up a living cell confirms the high content of such organic substances as proteins in it. There is a logical explanation for this fact: proteins perform various functions and are involved in all manifestations of cellular life.
For example, the protective function of proteins is the formation of antibodies - immunoglobulins produced by lymphocytes. Protective proteins such as thrombin, fibrin and thromboblastin provide blood clotting and prevent its loss during injuries and wounds. The composition of the cell includes complex proteins of cell membranes that have the ability to recognize foreign compounds - antigens. They change their configuration and inform the cell of potential danger (signaling function).
Some proteins have a regulatory function and are hormones, for example, oxytocin produced by the hypothalamus is reserved by the pituitary gland. From it toblood, oxytocin acts on the muscular walls of the uterus, causing it to contract. The protein vasopressin also has a regulatory function, controlling blood pressure.
In muscle cells there are actin and myosin that can contract, which determines the motor function of muscle tissue. Proteins also have a trophic function, 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 - they perform a transport function. If more energy-intensive substances such as carbohydrates and lipids are fully utilized, the cell proceeds to break down proteins. One gram of this substance gives 17.2 kJ of energy. One of the most important functions of proteins is catalytic (enzyme proteins accelerate chemical reactions occurring in the compartments 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.
Protein biosynthesis
Consider the process of protein synthesis in a cell, which 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, ribosomes are combined into polysomes. The main functions of ribosomes in a cell are the synthesis of protein molecules, which begins with the process of transcription. As a result, mRNA molecules are synthesized, to which polysomes are attached. Then the second process begins - translation. Transfer RNAscombine with twenty different types of amino acids and bring them to polysomes, and since the functions of ribosomes in a cell are the synthesis of polypeptides, these organelles form complexes with tRNA, and amino acid molecules bind to each other by peptide bonds, forming a 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 are studying, is on average 70% water, and in many animals leading an aquatic way of life (for example, coelenterates), 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 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.
The function of carbohydrates in the cell
As we found out earlier, carbohydrates are also important organic substances - polymers. These include polysaccharides, oligosaccharides and monosaccharides. Carbohydrates are part of more complex complexes - glycolipids and glycoproteins, from which cell membranes and supra-membrane structures, such as glycocalyx, are built.
In addition to carbon, carbohydrates contain oxygen and hydrogen atoms, and some polysaccharides also contain nitrogen, sulfur and phosphorus. There are a lot of carbohydrates in plant cells: potato tuberscontain up to 90% starch, seeds and fruits contain up to 70% carbohydrates, and in animal cells they are found 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 last two are the most common in the cells of living organisms, for example, ribose and deoxyribose are part of nucleic acids, and glucose and fructose take part in assimilation and dissimilation reactions. Oligosaccharides are often found in plant cells: sucrose is stored in the cells of sugar beet and sugar cane, m altose is found in germinated grains of rye and barley.
Disaccharides have a sweet taste and dissolve well in water. Polysaccharides, being biopolymers, are mainly represented 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 energy metabolism reactions, polysaccharides are broken down 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 starch and glycogen stores, in fact, are a reservoir of cellular energy.
Glycogen is stored mainly in muscle tissue and liver cells, vegetable starch in tubers, bulbs, roots, seeds, and in arthropods such as spiders, insects and crustaceans, trehalose oligosaccharide plays a major role in energy supply.
Carbohydratesdiffer from lipids and proteins in their ability to oxygen-free cleavage. This is extremely important for organisms that live in conditions of oxygen deficiency or absence, such as anaerobic bacteria and helminths - parasites of humans and animals.
There is another function of carbohydrates in the cell - building (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, olisaccharides, together with lipid and protein molecules, form a glycocalyx - an epimembrane complex. It provides adhesion - the adhesion of animal cells to each other, leading to the formation of tissues.
Lipids: structure and functions
These organic substances, which are hydrophobic (insoluble in water), can be extracted, that is, extracted from cells, using 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 the most abundant in all cell types.
Animals accumulate them in the subcutaneous adipose tissue, the nervous tissue contains fat in the form of myelin sheaths of nerves. It also accumulates in the kidneys, liver, in insects - in the fat body. Liquid fats - oils - are found in the seeds of many plants: cedar, peanut, sunflower, olive. The content of lipids in cells ranges from 5 to 90% (in adipose tissue).
Steroids and waxesdiffer from fats in that they do not have fatty acid residues in their molecules. So, steroids are hormones of the adrenal cortex that affect the puberty of the body and are components of testosterone. They are also found in vitamins (such as 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 splitting gives 38.9 kJ of energy - much more than other organic substances - proteins and carbohydrates. In addition, during the oxidation of 1 g of fat, almost 1.1 g is released. water. That is why some animals, having a supply of fat in their body, can be without water for a long time. For example, gophers can hibernate for more than two months without needing water, and a camel does not drink water when crossing the desert for 10–12 days.
The building function of lipids is that they are an integral part of cell membranes, and are also 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 injury. A specific thermal insulation function is inherent in animals that are in the water for a long time: whales, seals, fur 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 breakdown of organic substances and the release of a certain amount of energy accumulated in the form of molecules of adenosine triphosphoric acid.
Thus, with the complete oxidation of one mole of glucose, which occurs on the cristae of mitochondria, 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, occurring in cellular organelles - mitochondria. In prokaryotic organisms - phototrophic bacteria and cyanobacteria - the oxidation of nutrients occurs under the action of oxygen diffusing into cells on the internal outgrowths of plasma membranes.
We studied the chemical organization of cells, as well as the processes of protein biosynthesis and the function of oxygen in cellular energy metabolism.
