The cell is the basic elementary unit of all living things, therefore it has all the properties of living organisms: a highly ordered structure, receiving energy from the outside and using it to perform work and maintain order, metabolism, an active response to irritations, growth, development, reproduction, duplication and transmission of biological information to descendants, regeneration (restoration of damaged structures), adaptation to the environment.

German scientist T. Schwann in mid-19th century, created the cellular theory, the main provisions of which indicated that all tissues and organs consist of cells; cells of plants and animals are fundamentally similar to each other, they all arise in the same way; the activity of organisms is the sum of the vital activities of individual cells. Great influence on further development Cell theory and the theory of cells in general were influenced by the great German scientist R. Virchow. He not only brought together all the numerous disparate facts, but also convincingly showed that cells are a permanent structure and arise only through reproduction.

Cell theory in its modern interpretation includes the following main provisions: the cell is a universal elementary unit of living things; the cells of all organisms are fundamentally similar in their structure, function and chemical composition; cells reproduce only by dividing the original cell; multicellular organisms are complex cellular assemblies that form integral systems.

Thanks to modern methods studies have been identified two main cell types: more complexly organized, highly differentiated eukaryotic cells (plants, animals and some protozoa, algae, fungi and lichens) and less complexly organized prokaryotic cells (blue-green algae, actinomycetes, bacteria, spirochetes, mycoplasmas, rickettsia, chlamydia).

Unlike a prokaryotic cell, a eukaryotic cell has a nucleus bounded by a double nuclear membrane and a large number of membrane organelles.

ATTENTION!

The cell is the basic structural and functional unit of living organisms, carrying out growth, development, metabolism and energy, storing, processing and implementing genetic information. From a morphological point of view, a cell is a complex system of biopolymers, separated from external environment plasma membrane (plasmolemma) and consisting of a nucleus and cytoplasm in which organelles and inclusions (granules) are located.

What types of cells are there?

Cells are diverse in their shape, structure, chemical composition and nature of metabolism.

All cells are homologous, i.e. have a number of common structural features on which the performance of basic functions depends. Cells are characterized by unity of structure, metabolism (metabolism) and chemical composition.

At the same time, different cells also have specific structures. This is due to their performance of special functions.

Cell structure

Ultramicroscopic cell structure:

1 - cytolemma (plasma membrane); 2 - pinocytotic vesicles; 3 - centrosome, cell center (cytocenter); 4 - hyaloplasm; 5 - endoplasmic reticulum: a - granular network membrane; b - ribosomes; 6 - connection of the perinuclear space with the cavities of the endoplasmic reticulum; 7 - core; 8 - nuclear pores; 9 - non-granular (smooth) endoplasmic reticulum; 10 - nucleolus; 11 - internal reticular apparatus (Golgi complex); 12 - secretory vacuoles; 13 - mitochondria; 14 - liposomes; 15 - three successive stages of phagocytosis; 16 - connection of the cell membrane (cytolemma) with the membranes of the endoplasmic reticulum.

Chemical composition of the cell

The cell contains more than 100 chemical elements, four of which account for about 98% of the mass; these are organogens: oxygen (65–75%), carbon (15–18%), hydrogen (8–10%) and nitrogen (1 .5–3.0%). The remaining elements are divided into three groups: macroelements - their content in the body exceeds 0.01%); microelements (0.00001–0.01%) and ultramicroelements (less than 0.00001).

Macroelements include sulfur, phosphorus, chlorine, potassium, sodium, magnesium, calcium.

Microelements include iron, zinc, copper, iodine, fluorine, aluminum, copper, manganese, cobalt, etc.

Ultramicroelements include selenium, vanadium, silicon, nickel, lithium, silver and more. Despite their very low content, microelements and ultramicroelements play a very important role. They mainly affect metabolism. Without them, the normal functioning of each cell and the organism as a whole is impossible.

The cell consists of inorganic and organic substances. Among inorganic greatest number water. The relative amount of water in the cell is between 70 and 80%. Water is a universal solvent; all biochemical reactions in the cell take place in it. With the participation of water, thermoregulation is carried out. Substances that dissolve in water (salts, bases, acids, proteins, carbohydrates, alcohols, etc.) are called hydrophilic. Hydrophobic substances (fats and fat-like substances) do not dissolve in water. Others don't organic matter(salts, acids, bases, positive and negative ions) range from 1.0 to 1.5%.

Among organic substances, proteins (10–20%), fats or lipids (1–5%), carbohydrates (0.2–2.0%), and nucleic acids (1–2%) predominate. The content of low molecular weight substances does not exceed 0.5%.

A protein molecule is a polymer that consists of a large number of repeating units of monomers. Amino acid protein monomers (20 of them) are connected to each other by peptide bonds, forming a polypeptide chain (the primary structure of the protein). It twists into a spiral, forming, in turn, the secondary structure of the protein. Due to the specific spatial orientation of the polypeptide chain, the tertiary structure of the protein arises, which determines the specificity and biological activity of the protein molecule. Several tertiary structures combine with each other to form a quaternary structure.

Proteins perform essential functions. Enzymes are biological catalysts that increase speed chemical reactions hundreds of thousands of millions of times in a cell are proteins. Proteins, being part of all cellular structures, perform a plastic (construction) function. Cell movements are also carried out by proteins. They provide transport of substances into the cell, out of the cell and within the cell. The protective function of proteins (antibodies) is important. Proteins are one of the sources of energy. Carbohydrates are divided into monosaccharides and polysaccharides. The latter are built from monosaccharides, which, like amino acids, are monomers. Among the monosaccharides in the cell, the most important are glucose, fructose (contains six carbon atoms) and pentose (five carbon atoms). Pentoses are part of nucleic acids. Monosaccharides are highly soluble in water. Polysaccharides are poorly soluble in water (glycogen in animal cells, starch and cellulose in plant cells). Carbohydrates are a source of energy; complex carbohydrates combined with proteins (glycoproteins), fats (glycolipids) are involved in the formation of cell surfaces and cell interactions.

Lipids include fats and fat-like substances. Fat molecules are built from glycerol and fatty acids. Fat-like substances include cholesterol, some hormones, and lecithin. Lipids, which are the main components of cell membranes, thereby perform a construction function. Lipids are the most important sources of energy. So, if with complete oxidation of 1 g of protein or carbohydrates 17.6 kJ of energy is released, then with complete oxidation of 1 g of fat - 38.9 kJ. Lipids carry out thermoregulation and protect organs (fat capsules).

DNA and RNA

Nucleic acids are polymer molecules formed by nucleotide monomers. A nucleotide consists of a purine or pyrimidine base, a sugar (pentose) and a phosphoric acid residue. In all cells, there are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), which differ in the composition of bases and sugars.

Spatial structure of nucleic acids:

(according to B. Alberts et al., with modification). I - RNA; II - DNA; ribbons - sugar phosphate backbones; A, C, G, T, U are nitrogenous bases, the lattices between them are hydrogen bonds.

DNA molecule

A DNA molecule consists of two polynucleotide chains twisted around one another in the form double helix. The nitrogenous bases of both chains are connected to each other by complementary hydrogen bonds. Adenine combines only with thymine, and cytosine with guanine (A - T, G - C). DNA contains genetic information that determines the specificity of the proteins synthesized by the cell, that is, the sequence of amino acids in the polypeptide chain. DNA transmits by inheritance all the properties of a cell. DNA is found in the nucleus and mitochondria.

RNA molecule

An RNA molecule is formed by one polynucleotide chain. There are three types of RNA in cells. Informational, or messenger RNA tRNA (from the English messenger - “intermediary”), which transfers information about the nucleotide sequence of DNA to ribosomes (see below). Transfer RNA (tRNA), which carries amino acids to ribosomes. Ribosomal RNA (rRNA), which is involved in the formation of ribosomes. RNA is found in the nucleus, ribosomes, cytoplasm, mitochondria, and chloroplasts.

Composition of nucleic acids.

Cell biology is generally known to everyone school curriculum. We invite you to remember what you once learned, and also discover something new about it. The name “cell” was proposed back in 1665 by the Englishman R. Hooke. However, it was only in the 19th century that it began to be studied systematically. Scientists were interested, among other things, in the role of cells in the body. They can be part of many different organs and organisms (eggs, bacteria, nerves, red blood cells) or be independent organisms (protozoa). Despite all their diversity, there is much in common in their functions and structure.

Cell functions

They are all different in form and often in function. The cells of tissues and organs of the same organism can differ quite greatly. However, cell biology highlights functions that are common to all of their varieties. This is where protein synthesis always occurs. This process is controlled. A cell that does not synthesize proteins is essentially dead. A living cell is one whose components are constantly changing. However, the main classes of substances remain unchanged.

All processes in the cell are carried out using energy. These are nutrition, breathing, reproduction, metabolism. Therefore, a living cell is characterized by the fact that energy exchange occurs in it all the time. Each of them has a common the most important property- the ability to store energy and spend it. Other functions include division and irritability.

All living cells can respond to chemical or physical changes in their environment. This property is called excitability or irritability. In cells, when excited, the rate of breakdown of substances and biosynthesis, temperature, and oxygen consumption change. In this state, they perform the functions inherent to them.

Cell structure

Its structure is quite complex, although it is considered the simplest form of life in a science such as biology. The cells are located in the intercellular substance. It provides them with breathing, nutrition and mechanical strength. The nucleus and cytoplasm are the main components of every cell. Each of them is covered with a membrane, the building element of which is a molecule. Biology has established that the membrane consists of many molecules. They are arranged in several layers. Thanks to the membrane, substances penetrate selectively. In the cytoplasm there are organelles - the smallest structures. These are the endoplasmic reticulum, mitochondria, ribosomes, cell center, Golgi complex, lysosomes. You will better understand what cells look like by studying the pictures presented in this article.

Membrane

Endoplasmic reticulum

This organelle was named so due to the fact that it is located in the central part of the cytoplasm (with Greek language the word "endon" translates as "inside"). EPS - a very branched system of vesicles, tubes, tubules various shapes and magnitude. They are delimited by membranes.

There are two types of EPS. The first is granular, which consists of cisterns and tubules, the surface of which is strewn with granules (grains). The second type of EPS is agranular, that is, smooth. Ribosomes are grana. It is curious that granular EPS is mainly observed in the cells of animal embryos, while in adult forms it is usually agranular. As you know, ribosomes are the site of protein synthesis in the cytoplasm. Based on this, we can make the assumption that granular EPS occurs predominantly in cells where active protein synthesis occurs. The agranular network is believed to be represented mainly in those cells where active synthesis of lipids, that is, fats and various fat-like substances, occurs.

Both types of EPS do not just take part in the synthesis of organic substances. Here these substances accumulate and are also transported to the necessary places. EPS also regulates the metabolism that occurs between environment and a cell.

Ribosomes

Mitochondria

Energy organelles include mitochondria (pictured above) and chloroplasts. Mitochondria are a kind of energy station of each cell. It is in them that energy is extracted from nutrients. Mitochondria vary in shape, but are most often granules or filaments. Their number and size are not constant. It depends on the functional activity of a particular cell.

If you look at an electron micrograph, you will notice that mitochondria have two membranes: inner and outer. The inner one forms projections (cristae) covered with enzymes. Due to the presence of cristae, the total surface area of ​​mitochondria increases. This is important for enzyme activity to proceed actively.

Scientists have discovered specific ribosomes and DNA in mitochondria. This allows these organelles to reproduce independently during cell division.

Chloroplasts

As for chloroplasts, the shape is a disk or a ball with a double shell (inner and outer). Inside this organelle there are also ribosomes, DNA and grana - special membrane formations connected both to the inner membrane and to each other. Chlorophyll is located precisely in gran membranes. Thanks to it, the energy from sunlight is converted into the chemical energy adenosine triphosphate (ATP). In chloroplasts it is used for the synthesis of carbohydrates (formed from water and carbon dioxide).

Agree, you need to know the information presented above not only in order to pass the biology test. A cell is the building material that makes up our body. Yes and all Live nature- a complex collection of cells. As you can see, they have many components. At first glance, it may seem that studying the structure of a cell is not an easy task. However, if you look at it, this topic is not so complicated. It is necessary to know it in order to be well versed in a science such as biology. The composition of the cell is one of its fundamental themes.

Chemical substances in the cell, especially their composition, from a chemical point of view are divided into macro- and microelements. However, there is also a group of ultramicroelements, which includes chemical elements, the percentage of which is 0.0000001%.

Alone chemical compounds there are more in the cage, less of others. However, all the main elements of the cell belong to the group of macroelements. The prefix macro means a lot.

A living organism at the atomic level is no different from objects of inanimate nature. It consists of the same atoms as inanimate objects. However, the number of chemical elements in a living organism, especially those that provide basic life processes, is much greater in percentage terms.

Cell chemicals

Squirrels

The main substances of the cell are proteins. They occupy 50% of the cell mass. Proteins perform many different functions in the body of living things, and proteins are also many other substances in their likeness and functions.

In my own way chemical structure proteins are biopolymers that consist of amino acids connected by peptide bonds. I would like to note that the composition of proteins is mainly occupied by amino acid residues.

The chemical composition of proteins is characterized by a constant average amount of nitrogen - approximately 16%. I would like to note that under the influence of specific enzymes, as well as during heating with acids, proteins are amenable to hydrolysis. This is one of their main features.

Carbohydrates

Carbohydrates are very widespread in nature and play a very important role in the life of plants and animals. They take part in various metabolic processes in the body and are components of many natural compounds.

Depending on the content, structure and physicochemical properties, carbohydrates are divided into two groups: simple - these are monosaccharides and complex - the condensation products of monosaccharides. Among complex carbohydrates, there are also two groups: oligosaccharides (the number of monosaccharide residues is from two to ten) and polysaccharides (the number of monosaccharide residues is more than ten).

Lipids

Lipids are the main source of energy for organisms. In living organisms, lipids perform at least three main functions: they are the main structural components membranes, are a common energy reserve, and also play a protective role in the composition of the integument of animals, plants and microorganisms.

Chemical substances in the cell, which belong to the class of lipids, have a special property - they are insoluble in water and slightly soluble in organic solvents.

Nucleic acids

Two types of vital nucleic acids have been found in the cells of living organisms: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are complex compounds that contain nitrogen.

In the case of complete hydrolysis, nucleic acids are broken down into smaller compounds, namely: nitrogenous bases, carbohydrates and phosphate acid. In the case of incomplete hydrolysis of nucleic acids, nucleosides and nucleotides are created. The main function of nucleic acids is the storage of genetic information and the transport of biologically active substances.

A group of macroelements is the main source of cell life

The group of macroelements includes such basic chemical elements as oxygen, carbon, hydrogen, nitrogen, potassium, phosphorus, sulfur, magnesium, sodium, calcium, chlorine and others. Many of them, for example, phosphorus, nitrogen, sulfur are part of various compounds that are responsible for the life processes of body cells. Each of these elements has its own function, without which the existence of the cell would be impossible.

• Oxygen, for example, is included in almost all organic substances and compounds of the cell. For many, especially aerobic organisms, oxygen acts as an oxidizing agent, which provides the cells of this organism with energy during their respiration. The largest amount of oxygen in living organisms is found in water molecules.
• Carbon is also part of many cell compounds. The carbon atoms in the CaCO3 molecule form the basis of the skeleton of living organisms. Moreover, carbon regulates cellular functions and plays an important role in the process of plant photosynthesis.
• Hydrogen is found in water molecules in the cell. Its main role in cell structure is that many microscopic bacteria oxidize hydrogen in order to obtain energy.
• Nitrogen is one of the main components of the cell. Its atoms are part of nucleic acids, many proteins and amino acids. Nitrogen is involved in the process of regulating blood pressure in the form of N O and is excreted from the living body in urine.

Sulfur and phosphorus are no less important for the life of organisms. The first is contained in many amino acids, and therefore in proteins. And phosphorus forms the basis of ATP - the main and largest source of energy of a living organism. Moreover, phosphorus in the form of mineral salts is found in dental and bone tissues.

Calcium and magnesium are important components of body cells. Calcium clots blood, so it is vital for living beings. It also regulates many intracellular processes. Magnesium is involved in the creation of DNA in the body, moreover, it is a cofactor for many enzymes.

The cell also needs macroelements such as sodium and potassium. Sodium maintains the membrane potential of the cell, and potassium is necessary for nerve impulses and normal functioning of the heart muscles.

The importance of microelements for a living organism

All basic cell substances consist not only of macroelements, but also of microelements. These include zinc, selenium, iodine, copper and others. In the cell, as part of the main substances, they are found in minute quantities, but they play vital role in body processes. Selenium, for example, regulates many basic processes, copper is one of the constituent components of many enzymes, and zinc is the main element in the composition of insulin, the main hormone of the pancreas.

Chemical composition of a cell - video