The chemical composition of the cell

Chemical elements of the cell.

All cells, regardless of the level of organization, are similar in chemical composition. The cell contains several thousand substances that are involved in a variety of chemical reactions. In living organisms, about 80 chemical elements of the periodic system of D.I. Mendeleev were found. For 24 elements, the functions that they perform in the body are known, these are biogenic elements. According to the quantitative content in living matter, elements are divided into three categories:

Macronutrients:

O, C, H, N- about 98% of the mass of living matter, elements of the 1st group;

K, Na, Ca, Mg, S, P, Cl, F e - elements of the 2nd group. (1.9% of the mass of living matter).

trace elements (Zn, Mn, Cu, Co, Mo and many others), the share of which ranges from 0.001% to 0.000001. Trace elements are part of biologically active substances - enzymes, vitamins and hormones.

Ultramicroelements (Au, U, Ra, etc.), the concentration of which does not exceed 0.000001%. The role of most elements of this group has not yet been elucidated.

Macro- and microelements are present in living matter in the form of various chemical compounds, which are divided into inorganic and organic substances .

Inorganic compounds of the cell.

Inorganic substances include: water, making up about 70-80% of body weight; minerals - 1-1,5%.

Water. The most common inorganic compound in living organisms. Its content varies widely: in the cells of tooth enamel, water is about 10% by weight, and in the cells of a developing embryo - more than 90%.

Life is impossible without water. It is not only an essential component of living cells, but also the habitat of organisms. The biological significance of water is based on its chemical and physical properties.

The chemical and physical properties of water are explained, first of all, by the small size of water molecules, their polarity and the ability to combine with each other by hydrogen bonds. In a water molecule, one oxygen atom is covalently bonded to two hydrogen atoms. The molecule is polar: an oxygen atom carries a small negative charge, and two hydrogen atoms carry a small positive charge. This makes the water molecule a dipole. Therefore, when water molecules interact with each other, hydrogen bonds are established between them. They are 15-20 times weaker than covalent, but since each water molecule is capable of forming 4 hydrogen bonds, they significantly affect the physical properties of water. The large heat capacity, heat of fusion and heat of vaporization are explained by the fact that most of the heat absorbed by water is spent on breaking the hydrogen bonds between its molecules. Water has a high thermal conductivity. Water practically does not compress, it is transparent in the visible part of the spectrum. Finally, water is a substance whose density in the liquid state is greater than in the solid state, at 4 ° C it has a maximum density, ice has a lower density, it rises to the surface and protects the reservoir from freezing.

Its physical and chemical properties make it a unique liquid and determine its biological significance. Water is a good solvent for ionic (polar) as well as some non-ionic compounds that contain charged (polar) groups in their molecules. Any polar compounds in water hydrated(surrounded by water molecules), while water molecules participate in the formation of the structure of molecules of organic substances. If the energy of attraction of water molecules to the molecules of a substance is greater than the energy of attraction between the molecules of a substance, then the substance dissolves. In relation to water, there are: hydrophilic substances - substances that are highly soluble in water; hydrophobic substances Substances that are practically insoluble in water. Most biochemical reactions can only take place in an aqueous solution; many substances enter the cell and are excreted from it in an aqueous solution. The large heat capacity and thermal conductivity of water contribute to the uniform distribution of heat in the cell.

Due to the large loss of heat during the evaporation of water, the body is cooled. Thanks to the forces of adhesion and cohesion, water is able to rise through the capillaries (one of the factors that ensure the movement of water in the vessels of plants). Water is a direct participant in many chemical reactions (hydrolytic breakdown of proteins, carbohydrates, fats, etc.). Determines the stress state of cell walls (turgor), and also performs a supporting function (hydrostatic skeleton, for example, in roundworms).

Minerals of the cell. They are mainly represented by salts that dissociate into anions and cations. For the life processes of the cell, the most important cations are K +, Na +, Ca 2+, Mg 2+, anions HPO 4 2-, Cl -, HCO 3 -. The concentrations of ions in the cell and its environment are different. For example, in the external environment (blood plasma, sea water) K + is always less, and Na + is always more than in the cell. There are a number of mechanisms that allow the cell to maintain a certain ratio of ions in the protoplast and the environment.

Various ions take part in many life processes of the cell: cations K + , Na + , Cl - provide the excitability of living organisms; cations Mg 2+ , Mn 2+ , Zn 2+ , Ca 2+ and others are necessary for the normal functioning of many enzymes; the formation of carbohydrates during photosynthesis is impossible without Mg 2+ (an integral part of chlorophyll); the buffer properties of the cell (maintaining a slightly alkaline reaction of the contents of the cell) is supported by anions of weak acids (HCO 3 -, HPO 4 -) and weak acids (H 2 CO 3);

Phosphate buffer system:

Low pH High pH

HPO 4 2- + H + ←―――――――→H 2 PO 4 -

Hydrophosphate - ion Dihydrogen phosphate - ion

Bicarbonate Buffer System:

Low pH High pH

HCO 3 - + H + ←―――――――→ H 2 CO 3

Bicarbonate - ion Carbonic acid

Some inorganic substances are contained in the cell not only in a dissolved state, but also in a solid state. For example, Ca and P are found in bone tissue, in mollusk shells in the form of double carbonic and phosphate salts.

The chemical elements that make up the cell.

The composition of a living cell includes about 60 chemical elements of the periodic system of D. and Mendeleev. Moreover, many of them have the smallest serial numbers. And the lower the serial number of a chemical element, the more often it is found in wildlife.

All chemical elements that make up the cell can be divided into
3 groups by occurrence:

1) macroelements: carbon, hydrogen, oxygen and nitrogen. Their number in the cell is the largest, is about 98%. These elements are part of the protein.

2) oligoelements or average occurrence. There are 8 of them: 5 of them are metals (sodium, potassium, calcium, magnesium and iron) and 3 are non-metals (sulphur, phosphorus and chlorine). The share of oligoelements in the cell accounts for 1.9%.

3) trace elements. There are very few of them in the cell, about 0.1% for more than 40 elements. These are iodine, zinc, copper, fluorine, etc. Lack or absence of microelements can cause serious diseases. For example, a lack of iodine causes dysfunction of the thyroid gland, resulting in the development of a goiter.

According to the chemical composition, the substances entering the cell are divided into 2 groups:

- Inorganic (also found in inanimate nature)

– Organic (characteristic only for living organisms)

Water . The amount of water in the cell is maximum and is 70-80%.

The role of water in the cell is very large:

1) Water is a universal solvent. Various organic and inorganic substances dissolve in it. Depending on how different substances dissolve in water, there are 2 groups of substances:

– hydrophilic(from the Greek hydor - water, phileo - love) - these are substances that are highly soluble in water. These include many salts, acids, proteins, carbohydrates, etc.

– hydrophobic(from the Greek hydor - water, phobos - fear) - these are insoluble or poorly soluble substances in water. These include fats and fat-like substances.

2) Most of the chemical processes in the cell proceed only in aqueous solutions. Water is directly involved in many chemical intracellular reactions (hydrolysis, i.e. the breakdown of proteins, fats and other substances).

3) The volume and elasticity of the cell depend on the amount of water in it.

4) Water has a high heat capacity, it provides thermoregulation of the cell.

Water molecules are polar and are able to form complexes of several molecules due to the occurrence of hydrogen bonds. When the ambient temperature rises, part of the heat is spent on breaking the hydrogen bonds between water molecules, while the temperature of the internal environment remains practically unchanged. When cooled, hydrogen bonds between water molecules reappear, and heat is released.

In addition to water, the cell contains weak acids, bases, and many salts.

salt in the cell are in a dissociated state. K +, Na + Ca 2+ Mg 2+ and HPO 2-, H 2 PO 4, HCO 3, Cl - are important in the life of the cell. With the help of anions of weak acids, the reaction of the internal environment of the cell, close to neutral (weakly alkaline), is maintained at an almost constant level.

The concentration of ions inside the cell and in the intercellular fluid is different. Particularly sharp differences are characteristic of Na + (located mainly in the intercellular fluid) and K + (contained in the cell in high concentration), which play an important role in the functioning of nerve and muscle fibers.

The content of various salts in the cell is maintained at a certain level. A significant change in their concentration can cause serious disturbances in the cell, and even its death. A decrease in Ca 2+ concentration in the blood of mammals causes convulsions and death. For normal contraction of the heart muscle, a certain ratio of K + , Na + Ca 2+ is necessary. When the balance of these ions changes, the work of the heart muscle is disrupted.

Often inorganic substances in the cell form complexes with proteins, carbohydrates and fats.

Water. Of the inorganic substances that make up the cell, water is the most important. Its amount is from 60 to 95% of the total cell mass. Water plays an essential role in the life of cells and living organisms in general. In addition to being part of their composition, for many organisms it is also a habitat.

The role of water in the cell is determined by its unique chemical and physical properties, mainly related to the small size of the molecules, the polarity of its molecules and their ability to form hydrogen bonds with each other.

Water as a component of biological systems performs the following important functions: cell chemical inorganic

Water is a universal solvent for polar substances, such as salts, sugars, alcohols, acids, etc. Substances that are readily soluble in water are called hydrophilic. When a substance goes into solution, its molecules or ions are allowed to move more freely; the reactivity of the substance increases accordingly. It is for this reason that most of the chemical reactions in the cell proceed in aqueous solutions. Its molecules are involved in many chemical reactions, for example, in the formation or hydrolysis of polymers. In the process of photosynthesis, water is an electron donor, a source of hydrogen ions and free oxygen.

Water does not dissolve or mix with non-polar substances, since it cannot form hydrogen bonds with them. Substances that are insoluble in water are called hydrophobic. Hydrophobic molecules or their parts are repelled by water, and in its presence are attracted to each other. Such interactions play an important role in ensuring the stability of membranes, as well as many protein molecules, nucleic acids, and a number of subcellular structures.

Water has a high specific heat capacity. It takes a lot of energy to break the hydrogen bonds that hold water molecules together. This property ensures the maintenance of the thermal balance of the body with significant temperature fluctuations in the environment. In addition, water has a high thermal conductivity, which allows the body to maintain the same temperature throughout its volume.

Water is characterized by a high heat of vaporization, i.e., the ability of molecules to carry away a significant amount of heat with them while cooling the body. Due to this property of water, which is manifested during sweating in mammals, thermal shortness of breath in crocodiles and other animals, transpiration in plants, their overheating is prevented.

Water has an exceptionally high surface tension. This property is very important for adsorption processes, for the movement of solutions through tissues (blood circulation, ascending and descending currents in plants). For many small organisms, surface tension allows them to float or glide across the surface of the water.

Water ensures the movement of substances in the cell and body, the absorption of substances and the excretion of metabolic products.

In plants, water determines the turgor of cells, and in some animals it performs supporting functions, being a hydrostatic skeleton (round and annelids, echinoderms).

Water is an integral part of lubricating fluids (synovial - in the joints of vertebrates, pleural - in the pleural cavity, pericardial - in the pericardial sac) and mucus (facilitate the movement of substances through the intestines, create a humid environment on the mucous membranes of the respiratory tract). It is part of saliva, bile, tears, sperm, etc.

mineral salts. salts in an aqueous solution decompose into cations and anions. Cations (K+, Na+, Ca 2+, Mg:+, NH4+) and anions (C 1, H 2P 04 -, HP 042-, HC 03 -, NO32--, SO4 2-) are of the greatest importance. only the content, but also the ratio of ions in the cell.

The difference between the number of cations and anions on the surface and inside the cell provides the emergence of an action potential, which underlies the occurrence of nerve and muscle excitation. The difference in the concentration of ions on different sides of the membrane is due to the active transfer of substances through the membrane, as well as the conversion of energy.

Phosphoric acid anions create a phosphate buffer system that maintains the pH of the intracellular environment of the body at a level of 6.9.

Carbonic acid and its anions form a bicarbonate buffer system that maintains the pH of the extracellular medium (blood plasma) at 7.4.

Some ions are involved in the activation of enzymes, the creation of osmotic pressure in the cell, in the processes of muscle contraction, blood coagulation, etc.

A number of cations and anions are necessary for the synthesis of important organic substances (for example, phospholipids, ATP, nucleotides, hemoglobin, hemocyanin, chlorophyll, etc.), as well as amino acids, being sources of nitrogen and sulfur atoms.

Any cell contains not only organic substances. It consists of 70 elements from the periodic table. And 24 of them are found in cells of any type. The inorganic substances of the cell are also represented by water and ions.

All elements can be divided into three groups depending on their content:

• macroelements - N, C, H, O, Mg, Na, K, Ca, Fe, P, Cl, S;
• trace elements - B, Ni, Cu, Zn, Mb, Co;
• ultramicroelements - U, Ra, Hg, Au, Pb, Se.

According to another classification method, organelles are taken out separately from these groups - substances necessary for the synthesis of organic matter: water, carbon, oxygen and nitrogen.

The value of water

Water is one of the most important inorganic substances in the cell. Its necessity for any living being can hardly be overestimated, but few people know about all its functions in the cell. Let us briefly consider them in connection with those properties of water that allow it to fulfill its role.

1. Transpiration and perspiration - high heat capacity and good thermal conductivity.
2. Maintaining the shape - it is almost impossible to compress water so that it changes its volume.
3. Lubricating properties - viscosity.
4. Osmosis is the mobility of molecules due to the fragility of hydrogen bonds within the molecule.
5. Lymph, blood, gastric juice and other body fluids can use oxygen dissolved in water - water molecules are polar, it is a good solvent.
6. A dispersion medium is maintained in the cytoplasm (simultaneous existence in solution of two or more phases that do not mix with each other) - the formation of hydration membranes around large molecules, again due to the polarity of water molecules.

Macroelements, microelements and their role in the cell

Let us consider some of the functions of the elements in order to understand how important they are for the cell, although their content in it is small.

Magnesium - helps many enzymes to participate in DNA synthesis and energy metabolism.

Calcium - regulates the permeability of cell membranes.

Potassium - participates in protein synthesis and glycolysis, maintains the necessary bioelectric potential on the membrane (see how the sodium-potassium pump works).

Sulfur - is part of some amino acids, helps them create disulfide bridges (for the formation of the tertiary structure of the protein), participates in chemosynthesis and bacterial photosynthesis.

Iron - is part of the electron carrier enzymes in the photosynthesis system, is the center of the hemoglobin molecule.

Chlorine - its ions help the cell to remain electrically neutral.

Bromine is part of vitamin B1.

Copper - is part of the enzymes that are involved in the synthesis of cytochromes.

Zinc - found in enzymes necessary for alcoholic fermentation.

And this is not all the inorganic substances of the cell. It is very important to maintain the concentration of each substance at the right level. After all, their lack can significantly disrupt the functioning of the cell. However, as well as their excess.

The structure of the cell and all the processes occurring in it is a very large and complex system. All processes and methods of their regulation have been developed over centuries of evolution, everything in them is perfected and, under proper conditions, works stably and without errors.

Inorganic substances that make up the cell - video

Biology- the science of life. The most important task of biology is the study of the diversity, structure, life activity, individual development and evolution of living organisms, their relationship with the environment.

Living organisms have a number of features that distinguish them from inanimate nature. Individually, each of the differences is rather conditional, so they should be considered as a whole.

Signs that distinguish living matter from non-living:

1. the ability to reproduce and transfer hereditary information to the next generation;
2. metabolism and energy;
3. excitability;
4. adaptation to specific living conditions;
5. building material - biopolymers (the most important of them are proteins and nucleic acids);
6. specialization from molecules to organs and a high degree of their organization;
7. growth;
8. aging;
9. death.

Levels of organization of living matter:

1. molecular,
2. cellular,
3. fabric,
4. organ,
5. organismic,
6. population-species,
7. biogeocenotic,
8. biospheric.

Diversity of life

Nuclear-free cells were the first to appear on our planet. Most scientists accept that nuclear organisms appeared as a result of the symbiosis of ancient archaebacteria with blue-green algae and oxidizing bacteria (symbiogenesis theory).

Cytology

Cytology- the science of cage. Studies the structure and functions of cells of unicellular and multicellular organisms. A cell is an elementary unit of structure, functioning, growth and development of all living beings. Therefore, the processes and patterns characteristic of cytology underlie the processes studied by many other sciences (anatomy, genetics, embryology, biochemistry, etc.).

Chemical elements of the cell

Chemical element- a certain type of atoms with the same positive charge of the nucleus. About 80 chemical elements have been found in cells. They can be divided into four groups:
Group 1 - carbon, hydrogen, oxygen, nitrogen (98% of the contents of the cell),
group 2 - potassium, sodium, calcium, magnesium, sulfur, phosphorus, chlorine, iron (1.9%),
group 3 - zinc, copper, fluorine, iodine, cobalt, molybdenum, etc. (less than 0.01%),
Group 4 - gold, uranium, radium, etc. (less than 0.00001%).

Elements of the first and second groups in most manuals are called macronutrients, the elements of the third group are trace elements, the elements of the fourth group are ultramicroelements. For macro- and microelements, the processes and functions in which they participate have been clarified. For most ultramicroelements, the biological role has not been identified.

Chemical element	Substances containing a chemical element	Processes in which a chemical element is involved
Carbon, hydrogen, oxygen, nitrogen	Proteins, nucleic acids, lipids, carbohydrates and other organic substances	Synthesis of organic substances and the whole complex of functions carried out by these organic substances
Potassium, sodium	Na+ and K+	Ensuring the function of membranes, in particular, maintaining the electrical potential of the cell membrane, the operation of the Na + / Ka + pump, the conduction of nerve impulses, anionic, cationic and osmotic balances
Calcium	Ca +2	Participation in the process of blood clotting
	calcium phosphate, calcium carbonate	Bone tissue, tooth enamel, mollusk shells
	calcium pectate	Formation of the median lamina and cell wall in plants
Magnesium	Chlorophyll	Photosynthesis
Sulfur	Squirrels	Formation of the spatial structure of the protein due to the formation of disulfide bridges
Phosphorus	Nucleic acids, ATP	Synthesis of nucleic acids
Chlorine	Cl-	Maintaining the electric potential of the cell membrane, the operation of the Na + /Ka + -pump, the conduction of nerve impulses, anionic, cationic and osmotic balances
	HCl	Activation of digestive enzymes in the stomach
Iron	Hemoglobin	Oxygen transport
	Cytochromes	Electron transfer during photosynthesis and respiration
Manganese	Decarboxylases, dehydrogenases	Oxidation of fatty acids, participation in the processes of respiration and photosynthesis
Copper	Hemocyanin	Oxygen transport in some invertebrates
	Tyrosinase	melanin formation
Cobalt	Vitamin B 12	RBC formation
Zinc	Alcohol dehydrogenase	Anaerobic respiration in plants
	carbonic anhydrase	CO 2 transport in vertebrates
Fluorine	calcium fluoride	Bone tissue, tooth enamel
Iodine	thyroxine	regulation of basal metabolism
Molybdenum	Nitrogenase	Nitrogen fixation

Atoms of chemical elements in living organisms form inorganic(water, salt) and organic compounds(proteins, nucleic acids, lipids, carbohydrates). At the atomic level, there are no differences between living and non-living matter, differences will appear at the next, higher levels of organization of living matter.

Water

Water is the most common inorganic compound. The water content ranges from 10% (tooth enamel) to 90% of the cell mass (developing embryo). Life is impossible without water, the biological significance of water is determined by its chemical and physical properties.

The water molecule has an angular shape: hydrogen atoms form an angle of 104.5° with respect to oxygen. The part of the molecule where hydrogen is located is positively charged, the part where oxygen is negatively charged, in connection with this, the water molecule is a dipole. Hydrogen bonds form between water dipoles. Physical properties of water: transparent, maximum density - at 4 °C, high heat capacity, practically does not shrink; pure water is a poor conductor of heat and electricity, freezes at 0 °C, boils at 100 °C, etc. Chemical properties of water: good solvent, forms hydrates, enters into hydrolytic decomposition reactions, interacts with many oxides, etc. In relation to the ability to dissolve in water, there are: hydrophilic substances- highly soluble hydrophobic substances- practically insoluble in water.

Biological value of water:

1. is the basis of the internal and intracellular environment,
2. ensures the maintenance of the spatial structure,
3. provides transport of substances,
4. hydrates polar molecules,
5. serves as a solvent and diffusion medium,
6. participates in the reactions of photosynthesis and hydrolysis,
7. helps to cool the body
8. is a habitat for many organisms,
9. promotes migration and distribution of seeds, fruits, larval stages,
10. is the environment in which fertilization occurs,
11. in plants provides transpiration and seed germination,
12. contributes to the uniform distribution of heat in the body and many others. others

Other inorganic compounds of the cell

Other inorganic compounds are represented mainly by salts, which can be contained either in dissolved form (dissociated into cations and anions) or in solid form. Cations K + , Na + , Ca 2+ , Mg 2+ (see table above) and anions HPO 4 2- , Cl - , HCO 3 - are important for the life of the cell, providing buffer properties of the cell. buffering- the ability to maintain pH at a certain level (pH is the decimal logarithm of the reciprocal of the concentration of hydrogen ions). A pH value of 7.0 corresponds to a neutral solution, below 7.0 to an acidic solution, and above 7.0 to an alkaline solution. Cells and tissues are characterized by a slightly alkaline environment. Phosphate (1) and bicarbonate (2) buffer systems are responsible for maintaining this slightly alkaline reaction.