Diagram of the structure of a human cell. Biology: cells. Structure, purpose, functions. The structure of a human cell

Man, like all living beings, consists of cells interconnected by connecting structures.
The cells themselves behave like living beings, since they perform the same vital functions as multicellular organisms: they eat to support their livelihoods, use oxygen for energy, respond to certain stimuli, and have the ability to reproduce.

Lysosomes- organelles responsible for the digestion of substances entering the cytoplasm.

Ribosomes- organelles that synthesize proteins from amino acid molecules.

Cell or cytoplasmic membrane- semi-permeable structure surrounding the cell. Provides communication between the cell and the extracellular environment.

Cytoplasm- a substance that fills the entire cell and contains all cellular bodies, including the nucleus.

Microvilli– folds and bulges of the cytoplasmic membrane, ensuring the passage of substances through it.

Centrosome– participates in mitosis or cell division.

Centrioles– central parts of the centrosome.

Vacuoles- small vesicles in the cytoplasm filled with cellular fluid.

Core– one of the fundamental components of the cell, since the nucleus is the carrier of hereditary characteristics and influences reproduction and transmission of biological heredity.

Nuclear envelope– a porous membrane that regulates the passage of substances between the nucleus and the cytoplasm.

Nucleoli- spherical organelles of the nucleus involved in the formation of ribosomes.

Intracellular filaments- organelles contained in the cytoplasm.

Mitochondria- organelles that take part in a large number of chemical reactions, such as cellular respiration.

How we get energy: catabolism and anabolism 21.11.03 The nutritional functions of the cell are aimed at providing us with food and energy. 1 cell + mitosis = 2 cells 21.11.03 This type of mathematical formula is an easy way to remember the importance of the cell division process necessary for Cell or cytoplasmic membrane 21.11.03 The cytoplasmic membrane (envelope) is a thin structure that separates the contents of the cell from the environment. Cells, tissues, organs, systems and devices 21.11.03 The human body is a composite of elements that work together to effectively perform all vital functions. Stanley L. Miller's experiment on the origin of organic compounds 18.11.03 The earth was formed about 5 billion years ago. When its surface was sufficient, large amounts of ash and gases (hydrogen, measure) were erupted into the atmosphere. The high temperature contributed to the formation of huge clouds, which From parents to children thanks to chromosomes 21.11.03 The cell nucleus undergoes various changes when the cell begins to divide: the membrane and nucleoli disappear; at this time Mitochondria 21.11.03 Mitochondria are round or elongated organelles distributed throughout the cytoplasm Cell nucleus 21.11.03 The nucleus, one in every human cell, is its main component, as it is an organism

The cell is the basic structural and functional unit of all living organisms, except viruses. It has a specific structure, including many components that perform specific functions.

What science studies the cell?

Everyone knows that the science of living organisms is biology. The structure of a cell is studied by its branch - cytology.

What does a cell consist of?

This structure consists of a membrane, cytoplasm, organelles, or organelles, and a nucleus (absent in prokaryotic cells). The structure of cells of organisms belonging to different classes differs slightly. Significant differences are observed between the cell structure of eukaryotes and prokaryotes.

Plasma membrane

The membrane plays a very important role - it separates and protects the contents of the cell from the external environment. It consists of three layers: two protein layers and a middle phospholipid layer.

Cell wall

Another structure that protects the cell from external factors is located on top of the plasma membrane. Present in the cells of plants, bacteria and fungi. In the first it consists of cellulose, in the second - from murein, in the third - from chitin. In animal cells, a glycocalyx is located on top of the membrane, which consists of glycoproteins and polysaccharides.

Cytoplasm

It represents the entire cell space limited by the membrane, with the exception of the nucleus. The cytoplasm includes organelles that perform the main functions responsible for the life of the cell.

Organelles and their functions

The structure of a cell of a living organism involves a number of structures, each of which performs a specific function. They are called organelles, or organelles.

Mitochondria

They can be called one of the most important organelles. Mitochondria are responsible for the synthesis of energy necessary for life. In addition, they are involved in the synthesis of certain hormones and amino acids.

Energy in mitochondria is produced due to the oxidation of ATP molecules, which occurs with the help of a special enzyme called ATP synthase. Mitochondria are round or rod-shaped structures. Their number in an animal cell, on average, is 150-1500 pieces (this depends on its purpose). They consist of two membranes and a matrix - a semi-liquid mass that fills the internal space of the organelle. The main components of the shells are proteins; phospholipids are also present in their structure. The space between the membranes is filled with liquid. The mitochondrial matrix contains grains that accumulate certain substances, such as magnesium and calcium ions, necessary for energy production, and polysaccharides. Also, these organelles have their own protein biosynthesis apparatus, similar to that of prokaryotes. It consists of mitochondrial DNA, a set of enzymes, ribosomes and RNA. The structure of a prokaryotic cell has its own characteristics: it does not contain mitochondria.

Ribosomes

These organelles are composed of ribosomal RNA (rRNA) and proteins. Thanks to them, translation is carried out - the process of protein synthesis on an mRNA (messenger RNA) matrix. One cell can contain up to ten thousand of these organelles. Ribosomes consist of two parts: small and large, which combine directly in the presence of mRNA.

Ribosomes, which are involved in the synthesis of proteins necessary for the cell itself, are concentrated in the cytoplasm. And those with the help of which proteins are produced that are transported outside the cell are located on the plasma membrane.

Golgi complex

It is present only in eukaryotic cells. This organelle consists of dictosomes, the number of which is usually approximately 20, but can reach several hundred. The Golgi apparatus is included in the cell structure of only eukaryotic organisms. It is located near the nucleus and performs the function of synthesis and storage of certain substances, for example, polysaccharides. It produces lysosomes, which will be discussed below. This organelle is also part of the cell’s excretory system. Dictosomes are presented in the form of stacks of flattened disc-shaped cisterns. At the edges of these structures, vesicles form, containing substances that need to be removed from the cell.

Lysosomes

These organelles are small vesicles containing a set of enzymes. Their structure has one membrane covered with a layer of protein on top. The function performed by lysosomes is the intracellular digestion of substances. Thanks to the enzyme hydrolase, with the help of these organelles, fats, proteins, carbohydrates, and nucleic acids are broken down.

Endoplasmic reticulum (reticulum)

The cell structure of all eukaryotic cells also implies the presence of EPS (endoplasmic reticulum). The endoplasmic reticulum consists of tubes and flattened cavities with a membrane. This organelle comes in two types: rough and smooth network. The first is distinguished by the fact that ribosomes are attached to its membrane, the second does not have this feature. The rough endoplasmic reticulum performs the function of synthesizing proteins and lipids that are required for the formation of the cell membrane or for other purposes. Smooth takes part in the production of fats, carbohydrates, hormones and other substances, except proteins. The endoplasmic reticulum also performs the function of transporting substances throughout the cell.

Cytoskeleton

It consists of microtubules and microfilaments (actin and intermediate). The components of the cytoskeleton are polymers of proteins, mainly actin, tubulin or keratin. Microtubules serve to maintain the shape of the cell; they form organs of movement in simple organisms, such as ciliates, chlamydomonas, euglena, etc. Actin microfilaments also play the role of a framework. In addition, they are involved in the process of organelle movement. Intermediates in different cells are built from different proteins. They maintain the shape of the cell and also secure the nucleus and other organelles in a constant position.

Cell center

Consists of centrioles, which have the shape of a hollow cylinder. Its walls are formed from microtubules. This structure is involved in the process of division, ensuring the distribution of chromosomes between daughter cells.

Core

In eukaryotic cells it is one of the most important organelles. It stores DNA, which encrypts information about the entire organism, its properties, proteins that must be synthesized by the cell, etc. It consists of a shell that protects the genetic material, nuclear sap (matrix), chromatin and nucleolus. The shell is formed from two porous membranes located at some distance from each other. The matrix is represented by proteins; it forms a favorable environment inside the nucleus for storing hereditary information. The nuclear sap contains filamentous proteins that serve as support, as well as RNA. Also present here is chromatin, an interphase form of chromosome existence. During cell division, it turns from clumps into rod-shaped structures.

Nucleolus

This is a separate part of the nucleus responsible for the formation of ribosomal RNA.

Organelles found only in plant cells

Plant cells have some organelles that are not characteristic of any other organisms. These include vacuoles and plastids.

Vacuole

This is a kind of reservoir where reserve nutrients are stored, as well as waste products that cannot be removed due to the dense cell wall. It is separated from the cytoplasm by a specific membrane called the tonoplast. As the cell functions, individual small vacuoles merge into one large one - the central one.

Plastids

These organelles are divided into three groups: chloroplasts, leucoplasts and chromoplasts.

Chloroplasts

These are the most important organelles of a plant cell. Thanks to them, photosynthesis occurs, during which the cell receives the nutrients it needs. Chloroplasts have two membranes: outer and inner; matrix - the substance that fills the internal space; own DNA and ribosomes; starch grains; grains. The latter consist of stacks of thylakoids with chlorophyll, surrounded by a membrane. It is in them that the process of photosynthesis occurs.

Leukoplasts

These structures consist of two membranes, a matrix, DNA, ribosomes and thylakoids, but the latter do not contain chlorophyll. Leukoplasts perform a reserve function, accumulating nutrients. They contain special enzymes that make it possible to obtain starch from glucose, which, in fact, serves as a reserve substance.

Chromoplasts

These organelles have the same structure as those described above, however, they do not contain thylakoids, but there are carotenoids that have a specific color and are located directly next to the membrane. It is thanks to these structures that flower petals are painted a certain color, allowing them to attract pollinating insects.

Chemical composition of living organisms

The chemical composition of living organisms can be expressed in two forms: atomic and molecular. Atomic (elemental) composition shows the ratio of atoms of elements included in living organisms. Molecular (material) composition reflects the ratio of molecules of substances.

Chemical elements are part of cells in the form of ions and molecules of inorganic and organic substances. The most important inorganic substances in the cell are water and mineral salts, the most important organic substances are carbohydrates, lipids, proteins and nucleic acids.

Water is the predominant component of all living organisms. The average water content in the cells of most living organisms is about 70%.

Mineral salts in an aqueous cell solution dissociate into cations and anions. The most important cations are K+, Ca2+, Mg2+, Na+, NHJ, anions are Cl-, SO2-, HPO2-, H2PO-, HCO-, NO-.

Carbohydrates - organic compounds consisting of one or many molecules of simple sugars. The carbohydrate content in animal cells is 1-5%, and in some plant cells it reaches 70%.

Lipids - fats and fat-like organic compounds, practically insoluble in water. Their content in different cells varies greatly: from 2-3 to 50-90% in the cells of plant seeds and adipose tissue of animals.

Squirrels are biological heteropolymers whose monomers are amino acids. Only 20 amino acids are involved in the formation of proteins. They are called fundamental, or basic. Some of the amino acids are not synthesized in animals and humans and must come from plant foods (they are called essential).

Nucleic acids. There are two types of nucleic acids: DNA and RNA. Nucleic acids are polymers whose monomers are nucleotides.

Cell structure

The emergence of cell theory

Robert Hooke discovered cells in a section of cork in 1665 and first used the term “cell.”
Anthony van Leeuwenhoek discovered single-celled organisms.
Matthias Schleiden in 1838 and Thomas Schwann in 1839 formulated the basic principles of cell theory. However, they mistakenly believed that cells arise from a primary noncellular substance.
Rudolf Virchow proved in 1858 that all cells are formed from other cells through cell division.

Basic principles of cell theory

The cell is the structural unit of all living things. All living organisms are made up of cells (with the exception of viruses).
The cell is the functional unit of all living things. The cell exhibits the entire complex of vital functions.
The cell is the unit of development of all living things. New cells are formed only as a result of division of the original (mother) cell.
The cell is the genetic unit of all living things. The chromosomes of a cell contain information about the development of the entire organism.
The cells of all organisms are similar in chemical composition, structure and functions.

Types of Cellular Organization

Among living organisms, only viruses do not have a cellular structure. All other organisms are represented by cellular life forms. There are two types of cellular organization: prokaryotic and eukaryotic. Prokaryotes include bacteria, eukaryotes include plants, fungi and animals.

Prokaryotic cells are relatively simple. They do not have a nucleus, the area where DNA is located in the cytoplasm is called a nucleoid, the only DNA molecule is circular and not associated with proteins, the cells are smaller than eukaryotic ones, the cell wall includes a glycopeptide - murein, there are no membrane organelles, their functions are performed by invaginations of the plasma membrane, ribosomes are small, There are no microtubules, so the cytoplasm is motionless, and cilia and flagella have a special structure.

Eukaryotic cells have a nucleus in which chromosomes are located - linear DNA molecules associated with proteins; various membrane organelles are located in the cytoplasm.

Plant cells are distinguished by the presence of a thick cellulose cell wall, plastids, and a large central vacuole that displaces the nucleus to the periphery. The cell center of higher plants does not contain centrioles. The storage carbohydrate is starch.

Fungal cells have a cell wall containing chitin, a central vacuole in the cytoplasm, and no plastids. Only some fungi have a centriole in the cell center. The main reserve carbohydrate is glycogen.

Animal cells, as a rule, have a thin cell wall, do not contain plastids and a central vacuole; the cell center is characterized by a centriole. The storage carbohydrate is glycogen.

Structure of a eukaryotic cell

A typical eukaryotic cell has three components: the membrane, the cytoplasm, and the nucleus.

Cell membrane

Outside, the cell is surrounded by a membrane, the basis of which is the plasma membrane, or plasmalemma, which has a typical structure and thickness of 7.5 nm.

The cell membrane performs important and very diverse functions: determines and maintains the shape of the cell; protects the cell from the mechanical effects of penetration of damaging biological agents; carries out the reception of many molecular signals (for example, hormones); limits the internal contents of the cell; regulates the metabolism between the cell and the environment, ensuring the constancy of the intracellular composition; participates in the formation of intercellular contacts and various kinds of specific protrusions of the cytoplasm (microvilli, cilia, flagella).

The carbon component in the membrane of animal cells is called the glycocalyx.

The exchange of substances between the cell and its environment occurs constantly. The mechanisms of transport of substances into and out of the cell depend on the size of the transported particles. Small molecules and ions are transported by the cell directly across the membrane in the form of active and passive transport.

Depending on the type and direction, endocytosis and exocytosis are distinguished.

The absorption and release of solid and large particles are called phagocytosis and reverse phagocytosis, respectively; liquid or dissolved particles are called pinocytosis and reverse pinocytosis.

Cytoplasm

Cytoplasm is the internal contents of the cell and consists of hyaloplasm and various intracellular structures located in it.

Hyaloplasm (matrix) is an aqueous solution of inorganic and organic substances that can change their viscosity and are in constant motion. The ability to move or flow the cytoplasm is called cyclosis.

The matrix is an active environment in which many physical and chemical processes take place and which unites all the elements of the cell into a single system.

The cytoplasmic structures of the cell are represented by inclusions and organelles. Inclusions are relatively unstable, found in certain types of cells at certain moments of life, for example, as a supply of nutrients (starch grains, proteins, glycogen drops) or products to be released from the cell. Organelles are permanent and essential components of most cells, having a specific structure and performing a vital function.

The membrane organelles of a eukaryotic cell include the endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and plastids.

Endoplasmic reticulum. The entire internal zone of the cytoplasm is filled with numerous small channels and cavities, the walls of which are membranes similar in structure to the plasma membrane. These channels branch, connect with each other and form a network called the endoplasmic reticulum.

The endoplasmic reticulum is heterogeneous in its structure. There are two known types of it: granular and smooth. On the membranes of the channels and cavities of the granular network there are many small round bodies - ribosomes, which give the membranes a rough appearance. The membranes of the smooth endoplasmic reticulum do not carry ribosomes on their surface.

The endoplasmic reticulum performs many diverse functions. The main function of the granular endoplasmic reticulum is participation in protein synthesis, which occurs in ribosomes.

The synthesis of lipids and carbohydrates occurs on the membranes of the smooth endoplasmic reticulum. All these synthesis products accumulate in channels and cavities, and are then transported to various organelles of the cell, where they are consumed or accumulated in the cytoplasm as cellular inclusions. The endoplasmic reticulum connects the main organelles of the cell.

Golgi apparatus

In many animal cells, such as nerve cells, it takes the form of a complex network located around the nucleus. In the cells of plants and protozoa, the Golgi apparatus is represented by individual sickle- or rod-shaped bodies. The structure of this organelle is similar in the cells of plant and animal organisms, despite the diversity of its shape.

The Golgi apparatus includes: cavities bounded by membranes and located in groups (5-10); large and small bubbles located at the ends of the cavities. All these elements form a single complex.

The Golgi apparatus performs many important functions. The products of the cell's synthetic activity - proteins, carbohydrates and fats - are transported to it through the channels of the endoplasmic reticulum. All these substances first accumulate, and then, in the form of large and small bubbles, enter the cytoplasm and are either used in the cell itself during its life, or removed from it and used in the body. For example, in the cells of the mammalian pancreas, digestive enzymes are synthesized, which accumulate in the cavities of the organelle. Bubbles filled with enzymes then form. They are excreted from the cells into the pancreatic duct, from where they flow into the intestinal cavity. Another important function of this organelle is that on its membranes the synthesis of fats and carbohydrates (polysaccharides) occurs, which are used in the cell and which are part of the membranes. Thanks to the activity of the Golgi apparatus, renewal and growth of the plasma membrane occurs.

Mitochondria

The cytoplasm of most animal and plant cells contains small bodies (0.2-7 microns) - mitochondria (Greek "mitos" - thread, "chondrion" - grain, granule).

Mitochondria are clearly visible in a light microscope, with which you can examine their shape, location, and count their number. The internal structure of mitochondria was studied using an electron microscope. The mitochondrial shell consists of two membranes - outer and inner. The outer membrane is smooth, it does not form any folds or outgrowths. The inner membrane, on the contrary, forms numerous folds that are directed into the mitochondrial cavity. The folds of the inner membrane are called cristae (Latin “crista” - ridge, outgrowth). The number of cristae varies in the mitochondria of different cells. There can be from several tens to several hundred of them, and there are especially many cristae in the mitochondria of actively functioning cells, such as muscle cells.

Mitochondria are called the “power stations” of cells because their main function is the synthesis of adenosine triphosphoric acid (ATP). This acid is synthesized in the mitochondria of cells of all organisms and is a universal source of energy necessary for the vital processes of the cell and the whole organism.

New mitochondria are formed by the division of mitochondria already existing in the cell.

Lysosomes

They are small round bodies. Each lysosome is separated from the cytoplasm by a membrane. Inside the lysosome there are enzymes that break down proteins, fats, carbohydrates, and nucleic acids.

Lysosomes approach a food particle that has entered the cytoplasm, merge with it, and one digestive vacuole is formed, inside which there is a food particle surrounded by lysosome enzymes. Substances formed as a result of the digestion of food particles enter the cytoplasm and are used by the cell.

Having the ability to actively digest nutrients, lysosomes participate in the removal of cell parts, whole cells and organs that die during vital activity. The formation of new lysosomes occurs constantly in the cell. Enzymes contained in lysosomes, like any other proteins, are synthesized on ribosomes in the cytoplasm. These enzymes then travel through the endoplasmic reticulum to the Golgi apparatus, in the cavities of which lysosomes are formed. In this form, lysosomes enter the cytoplasm.

Plastids

Plastids are found in the cytoplasm of all plant cells. There are no plastids in animal cells. There are three main types of plastids: green - chloroplasts; red, orange and yellow - chromoplasts; colorless - leucoplasts.

Organelles that do not have a membrane structure are also required for most cells. These include ribosomes, microfilaments, microtubules, and the cell center.

Ribosomes. Ribosomes are found in the cells of all organisms. These are microscopic round bodies with a diameter of 15-20 nm. Each ribosome consists of two particles of unequal size, small and large.

One cell contains many thousands of ribosomes; they are located either on the membranes of the granular endoplasmic reticulum or lie freely in the cytoplasm. Ribosomes contain proteins and RNA. The function of ribosomes is protein synthesis. Protein synthesis is a complex process that is carried out not by one ribosome, but by a whole group, including up to several dozen united ribosomes. This group of ribosomes is called a polysome. Synthesized proteins first accumulate in the channels and cavities of the endoplasmic reticulum and are then transported to organelles and cell sites where they are consumed. The endoplasmic reticulum and ribosomes located on its membranes represent a single apparatus for the biosynthesis and transport of proteins.

Microtubules and microfilaments

Thread-like structures consisting of various contractile proteins and determining the motor functions of the cell. Microtubules look like hollow cylinders, the walls of which consist of proteins - tubulins. Microfilaments are very thin, long, thread-like structures composed of actin and myosin.

Microtubules and microfilaments permeate the entire cytoplasm of the cell, forming its cytoskeleton, causing cyclosis, intracellular movements of organelles, divergence of chromosomes during the division of nuclear material, etc.

Cellular center (centrosome). In animal cells, near the nucleus there is an organelle called the cell center. The main part of the cell center consists of two small bodies - centrioles, located in a small area of densified cytoplasm. Each centriole has the shape of a cylinder up to 1 µm long. Centrioles play an important role in cell division; they participate in the formation of the division spindle.

In the process of evolution, different cells adapted to living in different conditions and performing specific functions. This required the presence of special organelles in them, which are called specialized in contrast to the general-purpose organoids discussed above. These include contractile vacuoles of protozoa, muscle fiber myofibrils, neurofibrils and synaptic vesicles of nerve cells, microvilli of epithelial cells, cilia and flagella of some protozoa.

Core

The nucleus is the most important component of eukaryotic cells. Most cells have one nucleus, but multinucleated cells are also found (in a number of protozoa, in the skeletal muscles of vertebrates). Some highly specialized cells lose their nuclei (mammalian red blood cells, for example).

The nucleus, as a rule, has a spherical or oval shape, less often it can be segmented or fusiform. The nucleus consists of a nuclear envelope and karyoplasm containing chromatin (chromosomes) and nucleoli.

The nuclear envelope is formed by two membranes (outer and inner) and contains numerous pores through which various substances are exchanged between the nucleus and the cytoplasm.

Karyoplasm (nucleoplasm) is a jelly-like solution containing various proteins, nucleotides, ions, as well as chromosomes and the nucleolus.

The nucleolus is a small round body, intensely stained and found in the nuclei of non-dividing cells. The function of the nucleolus is the synthesis of rRNA and its connection with proteins, i.e. assembly of ribosomal subunits.

Chromatin is clumps, granules and filamentous structures formed by DNA molecules in complex with proteins that are specifically stained with certain dyes. Different sections of DNA molecules within chromatin have different degrees of helicalization, and therefore differ in color intensity and the nature of genetic activity. Chromatin is a form of existence of genetic material in non-dividing cells and provides the possibility of doubling and implementing the information contained in it. During cell division, DNA spirals and chromatin structures form chromosomes.

Chromosomes are dense, intensely stained structures that are units of morphological organization of genetic material and ensure its precise distribution during cell division.

The number of chromosomes in the cells of each biological species is constant. Usually in the nuclei of body cells (somatic) chromosomes are presented in pairs; in germ cells they are not pairs. A single set of chromosomes in germ cells is called haploid (n), while a set of chromosomes in somatic cells is called diploid (2n). Chromosomes of different organisms vary in size and shape.

A diploid set of chromosomes of cells of a particular type of living organism, characterized by the number, size and shape of chromosomes, is called a karyotype. In the chromosome set of somatic cells, paired chromosomes are called homologous, chromosomes from different pairs are called non-homologous. Homologous chromosomes are identical in size, shape, and composition (one is inherited from the maternal organism, the other from the paternal organism). Chromosomes as part of a karyotype are also divided into autosomes, or non-sex chromosomes, which are the same in male and female individuals, and heterochromosomes, or sex chromosomes, which are involved in sex determination and differ in males and females. The human karyotype is represented by 46 chromosomes (23 pairs): 44 autosomes and 2 sex chromosomes (females have two identical X chromosomes, males have X and Y chromosomes).

The nucleus stores and implements genetic information, controls the process of protein biosynthesis, and, through proteins, all other life processes. The nucleus is involved in the replication and distribution of hereditary information between daughter cells, and, consequently, in the regulation of cell division and development processes of the organism.

Cell biology is generally known to everyone from the 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 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 because it is located in the central part of the cytoplasm (from the Greek the word “endon” is translated as “inside”). The EPS is a very branched system of vesicles, tubes, and tubules of various shapes and sizes. 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. The EPS also regulates the metabolism that occurs between the environment and the 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. And all living nature is 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.

The elementary and functional unit of all life on our planet is the cell. In this article you will learn in detail about its structure, the functions of organelles, and also find the answer to the question: “How is the structure of plant and animal cells different?”

Cell structure

The science that studies the structure of the cell and its functions is called cytology. Despite their small size, these parts of the body have a complex structure. Inside is a semi-liquid substance called cytoplasm. All vital processes take place here and the component parts - organelles - are located. You can learn about their features below.

Core

The most important part is the core. It is separated from the cytoplasm by a shell, which consists of two membranes. They have pores so that substances can pass from the nucleus into the cytoplasm and vice versa. Inside there is nuclear juice (karyoplasm), in which the nucleolus and chromatin are located.

Rice. 1. Structure of the nucleus.

It is the nucleus that controls the life of the cell and stores genetic information.

The functions of the internal contents of the nucleus are the synthesis of protein and RNA. From them special organelles are formed - ribosomes.

Ribosomes

They are located around the endoplasmic reticulum, making its surface rough. Sometimes ribosomes are freely located in the cytoplasm. Their functions include protein biosynthesis.

TOP 4 articleswho are reading along with this

Endoplasmic reticulum

EPS can have a rough or smooth surface. The rough surface is formed due to the presence of ribosomes on it.

The functions of the EPS include protein synthesis and internal transport of substances. Part of the formed proteins, carbohydrates and fats enters special storage containers through the channels of the endoplasmic reticulum. These cavities are called the Golgi apparatus; they are presented in the form of stacks of “cisterns”, which are separated from the cytoplasm by a membrane.

Golgi apparatus

Most often located near the nucleus. Its functions include protein conversion and the formation of lysosomes. This complex stores substances that were synthesized by the cell itself for the needs of the whole organism, and will later be removed from it.

Lysosomes are presented in the form of digestive enzymes, which are enclosed by a membrane in vesicles and distributed throughout the cytoplasm.

Mitochondria

These organelles are covered with a double membrane:

smooth - outer shell;
cristae - an inner layer with folds and protrusions.

Rice. 2. The structure of mitochondria.

The functions of mitochondria are respiration and conversion of nutrients into energy. The cristae contain an enzyme that synthesizes ATP molecules from nutrients. This substance is a universal source of energy for all kinds of processes.

The cell wall separates and protects the internal contents from the external environment. It maintains shape, ensures communication with other cells, and ensures the metabolic process. The membrane consists of a double layer of lipids, between which there are proteins.

Comparative characteristics

Plant and animal cells differ from each other in their structure, size and shape. Namely:

the cell wall of a plant organism has a dense structure due to the presence of cellulose;
a plant cell has plastids and vacuoles;
an animal cell has centrioles, which are important in the process of division;
The outer membrane of an animal organism is flexible and can take on various shapes.

Rice. 3. Scheme of the structure of plant and animal cells.

The following table will help summarize knowledge about the main parts of the cellular organism:

Table "Cell structure"

*Organoid*	*Characteristic*	*Functions*
	It has a nuclear envelope, inside which contains nuclear juice with a nucleolus and chromatin.	Transcription and storage of DNA.
Plasma membrane	It consists of two layers of lipids, which are permeated with proteins.	Protects the contents, ensures intercellular metabolic processes, and responds to stimuli.
Cytoplasm	Semi-liquid mass containing lipids, proteins, polysaccharides, etc.	Association and interaction of organelles.
	Membrane bags of two types (smooth and rough)	Synthesis and transportation of proteins, lipids, steroids.
Golgi apparatus	Located near the nucleus in the form of vesicles or membrane sacs.	Forms lysosomes and removes secretions.
Ribosomes	They have protein and RNA.	They form protein.
Lysosomes	In the form of a bag containing enzymes.	Digestion of nutrients and dead parts.
Mitochondria	The outside is covered with a membrane and contains cristae and numerous enzymes.	Formation of ATP and protein.
Plastids	Covered with a membrane. They are represented by three types: chloroplasts, leucoplasts, chromoplasts.	Photosynthesis and storage of substances.
	Sacs with cell sap.	Regulate blood pressure and retain nutrients.
Centrioles	Has DNA, RNA, proteins, lipids, carbohydrates.	Participates in the process of division, forming a spindle.

What have we learned?

A living organism consists of cells that have a rather complex structure. On the outside, it is covered with a dense shell that protects the internal contents from the effects of the external environment. Inside there is a core that regulates all ongoing processes and stores the genetic code. Around the nucleus there is cytoplasm with organelles, each of which has its own characteristics and characteristics.