Everything in this world consists of different particles that make up a single picture, just like a living cell consists of organelles. The “unit of life” is covered with a protective barrier - a membrane that separates the outside world from the internal contents. The structure of cell organelles is a whole system that needs to be understood.

Eukaryotes and prokaryotes

In nature, there are a huge number of types of cells, only in the human body there are more than 200 of them, but only 2 types of cellular organization are known - eukaryotic and prokaryotic. Both types mentioned arose through evolution. Eukaryotes and prokaryotes have a cell membrane, but that's where their similarities end.

Cells of the prokaryotic species are small in size and cannot boast of a well-developed membrane. The main difference is the absence of a core. In some cases, plasmids are present, which are a ring of DNA molecules. Organelles are practically absent in such cells - only ribosomes are found. Prokaryotes include bacteria and archaea. Monera is what was previously called single-celled bacteria that do not have a nucleus. Today this term has fallen out of use.

The eukaryotic cell is much larger than prokaryotes and contains structures called organelles. Unlike its simplest “relative,” the eukaryotic cell has linear DNA, which is located in the nucleus. Another interesting difference between these two species is that mitochondria and plastids, which are located inside a eukaryotic cell, are strikingly reminiscent of bacteria in their structure and activity. Scientists have suggested that these organelles are descendants of prokaryotes, in other words, earlier prokaryotes entered into symbiosis with eukaryotes.

"Device" of a eukaryotic cell

Cell organelles are its small parts that perform important functions, for example, storage of genetic information, synthesis, division and others.

Organelles include:

• Cell membrane;
• Golgi complex;
• Ribosomes;
• Microfilaments;
• Chromosomes;
• Mitochondria;
• Endoplasmic reticulum;
• Microtubules;
• Lysosomes.

The structure of the organelles of animal, plant and human cells is the same, but each of them has its own characteristics. Animal cells are characterized by microfibrils and centrioles, while plant cells are characterized by plastids. A table of the structure of cell organelles will help you gather information together.

Some scientists classify the nucleus of a cell as its organelles. The core is located in the center and has an oval or round shape. Its porous shell consists of 2 membranes. The shell has two phases - interphase and division.

The cell nucleus has two functions - storing genetic information and protein synthesis. Thus, the core is not only a “repository”, but also a place where material is reproduced and functions.

Table: structure of cell organelles

Cell organelles	Organoid structure	Functions of the organoid
	1. Organelles with a membrane
Endoplasmic reticulum (ER).	A developed system of channels and various cavities that penetrate the entire cytoplasm. Single membrane structure.	Connection of cellular membrane structures. EPS is the “surface” on which intracellular processes occur. Substances are transported through the network system.
Golgi complex. located near the nucleus. A cell may have several Golgi complexes.	The complex is a system of bags that are stacked.	Transport of lipids and proteins that come from the EPS. Restructuring of these substances, “packaging” and accumulation.
Lysosomes.	Vesicles with one membrane containing enzymes.	They break down molecules, thereby participating in cell digestion.
Mitochondria.	The shape of mitochondria can be rod-shaped or oval. They have two membranes. Mitochondria contain a matrix containing DNA and RNA molecules.	Mitochondria are responsible for the synthesis of the energy source – ATP.
Plastids. They are present only in plant cells.	Most often, plastids are oval in shape. They have two membranes.	They have three types of plastids: leucoplasts, chloroplasts and chromoplasts. Leukoplasts accumulate organic substances. Chloroplasts are responsible for photosynthesis. Chromoplasts “color” the plant.
	2. Organelles that do not have a membrane
Ribosomes are present in all cells. They are located in the cytoplasm or connected to the membrane of the endoplasmic reticulum.	Consist of several molecules of RNA and protein. Magnesium ions support the structure of ribosomes. Ribosomes look like small sphere-shaped bodies.	Synthesis of polypeptide chains is carried out.
The cellular center is present in animal cells, except for a number of protozoa, and is also found in some plants.	The cell center consists of two cylindrical organelles - centrioles.	Participates in the division of achromatin verter. The organelles that make up the cell center produce flagella and cilia.
Myrofilaments, microtubules.	They are a plexus of filaments that penetrate the entire cytoplasm. These filaments are formed from contractile proteins.	They are part of the cell cytoskeleton. Responsible for the movement of organelles and contraction of fibers.

Cell organelles - video

Organoids(organelles)- in cytology, permanent specialized structures in the cells of living organisms. Each organelle performs certain functions vital for the cell. The term "Organoids" is explained by the comparison of these cell components with the organs of a multicellular organism. Organoids are contrasted with temporary inclusions of cells that appear and disappear during the metabolic process.

Sometimes only permanent cell structures located in its cytoplasm are considered organelles. Often, nuclei and intranuclear structures (for example, the nucleolus) are not called organelles. The cell membrane, cilia and flagella are also not usually classified as organelles.

Receptors and other small, molecular-level structures are not called organelles. The boundary between molecules and organelles is not very clear. Thus, ribosomes, which are usually unambiguously classified as organelles, can also be considered a complex molecular complex. Elements of the cytoskeleton (microtubules, thick filaments of striated muscles, etc.) are usually not classified as organelles.

In many ways, the set of organelles listed in training manuals is determined by tradition.

Cellular organelles (having a membrane structure)

Name	animal cell	plant cell
Core		System of genetic determination and regulation of protein metabolism
Endoplasmic reticulum granular (ER)		Synthesis of hormones, enzymes, plasma proteins, membranes; segregation (separation) of synthesized proteins; formation of membranes of the vacuolar system, plasmalemma, phospholipid synthesis
Smooth endoplasmic reticulum (ER)		Metabolism of lipids and some intracellular polysaccharides
Lamellar Golgi complex	polysaccharide synthesis	Secretion, segregation and accumulation of products synthesized in the EPS, polysaccharide synthesis
Primary lysosomes	Hydrolysis of biopolymers	Hydrolysis of biopolymers
Secondary lysosomes (see vacuole)		The result of phagocytosis, pinocytosis, transmembrane transport of substances
Autolysosome		Autolysis of cellular components
Peroxisomes	Oxidation of amino acids, formation of peroxides	Amino acid oxidation, peroxide formation, protective function
Mitochondria	ATP synthesis	ATP synthesis
Kinetoplast		Complex function: movement and power supply of movement
Plastids: chloroplasts chromatophores leukoplasts chromoplasts		Photosynthesis, synthesis and hydrolysis of secondary starch (amyloplasts); oils (elaioplasts); protein (proteinoplasts, proteoplasts)
Vacuole	Intracellular digestion	Accumulation of water and nutrients

Cellular organelles (having a non-membrane structure)

Name	animal cell	plant cell
Nucleolus		Place of formation of ribosomal RNA
Centrioles (centrosomes)		Spindle formation
Ribosomes	Protein synthesis	Protein synthesis
Microtubules		Cytoskeleton, participation in the transport of substances and organelles
Micro filaments		Contractile elements of the cytoskeleton, cell motility, intracellular movement of substances
Microfibrils		Contractile function of the cell and intracellular movement of organelles
Flagella	Organs of movement	Organs of movement
Cilia	Increased suction surface	Organs of movement, protection
Dictyosomes, desmosomes	High contact membranes	Organ of intercellular contact

Eukaryotic organelles

(general information)

Organelle	Main function	Structure	Organisms	Notes
Chloroplast (Plastids)	photosynthesis	double-membrane	plants, protista	have their own DNA; suggest that chloroplasts arose from cyanobacteria as a result of symbiogenesis
Endoplasmic reticulum	translation and folding of new proteins (granular endoplasmic reticulum), lipid synthesis (agranular endoplasmic reticulum)	single-membrane	all eukaryotes	on the surface of the granular endoplasmic reticulum there is a large number of ribosomes, folded like a bag; agranular endoplasmic reticulum is rolled into tubes
Golgi apparatus	protein sorting and conversion	single-membrane	All eukaryotes	asymmetric - cisterns located closer to the cell nucleus contain the least mature proteins, and vesicles containing fully mature proteins bud from cisterns located further from the nucleus
Mitochondria	energy	double-membrane	most eukaryotes	have their own mitochondrial DNA; suggest that mitochondria arose as a result of symbiogenesis
Vacuole	reserve, maintaining homeostasis, in plant cells - maintaining cell shape (turgor)	single membrane	eukaryotes, more pronounced in plants
Core	DNA storage, RNA transcription	double-membrane	all eukaryotes	contains the bulk of the genome
Ribosomes	protein synthesis based on messenger RNA using transport RNA	RNA/protein	eukaryotes, prokaryotes
Vesicles	store or transport nutrients	single membrane	all eukaryotes
Lysosomes	small labile formations containing enzymes, in particular hydrolases, involved in the processes of digestion of phagocytosed food and autolysis (self-dissolution of organelles)	single membrane	most eukaryotes
Centrioles (cell center)	Center of cytoskeletal organization. Necessary for the process of cell division (evenly distributes chromosomes)	non-membrane	eukaryotes
Melanosome	pigment storage	single membrane	animals
Myofibrils	contraction of muscle fibers	complexly organized bundle of protein filaments	animals

It is assumed that mitochondria And plastids- these are former symbionts of the cells containing them, once independent prokaryotes

Organelles are structures that are constantly present in the cytoplasm and are specialized to perform certain functions. Based on the principle of organization, membrane and non-membrane cell organelles are distinguished.

Membrane cell organelles

1. Endoplasmic reticulum (ER) - a system of internal membranes of the cytoplasm, forming large cavities - cisterns and numerous tubules; occupies a central position in the cell, around the nucleus. EPS makes up up to 50% of the cytoplasm volume. ER channels connect all cytoplasmic organelles and open into the perinuclear space of the nuclear envelope. Thus, the ER is an intracellular circulatory system. There are two types of membranes of the endoplasmic reticulum - smooth and rough (granular). However, it is necessary to understand that they are part of one continuous endoplasmic reticulum. Ribosomes are located on granular membranes, where protein synthesis occurs. Enzyme systems involved in the synthesis of fats and carbohydrates are arranged in an orderly manner on smooth membranes.

2. The Golgi apparatus is a system of cisterns, tubules and vesicles formed by smooth membranes. This structure is located on the periphery of the cell in relation to the EPS. Enzyme systems involved in the formation of more complex organic compounds from proteins, fats and carbohydrates synthesized in the ER are arranged in an orderly manner on the membranes of the Golgi apparatus. Membrane assembly and lysosome formation occur here. The membranes of the Golgi apparatus ensure the accumulation, concentration and packaging of secretions released from the cell.

3. Lysosomes are membrane organelles containing up to 40 proteolytic enzymes capable of breaking down organic molecules. Lysosomes are involved in the processes of intracellular digestion and apoptosis (programmed cell death).

4. Mitochondria are the energy stations of the cell. Double-membrane organelles with a smooth outer and inner membrane forming cristae - ridges. On the inner surface of the inner membrane, enzyme systems involved in ATP synthesis are arranged in an orderly manner. Mitochondria contain a circular DNA molecule, similar in structure to the chromosome of prokaryotes. There are many small ribosomes on which protein synthesis occurs, partially independent of the nucleus. However, the genes enclosed in a circular DNA molecule are not sufficient to provide all aspects of the life of mitochondria, and they are semi-autonomous structures of the cytoplasm. An increase in their number occurs due to division, which is preceded by the doubling of the circular DNA molecule.

5. Plastids are organelles characteristic of plant cells. There are leucoplasts - colorless plastids, chromoplasts, which have a red-orange color, and chloroplasts. - green plastids. All of them have a single structural plan and are formed by two membranes: the outer (smooth) and the inner, forming partitions - stromal thylakoids. On the thylakoids of the stroma there are grana, consisting of flattened membrane vesicles - grana thylakoids, stacked one on top of the other like coin columns. The thylakoids of the grana contain chlorophyll. The light phase of photosynthesis takes place here - in the grana, and the dark phase reactions - in the stroma. Plastids contain a ring-shaped DNA molecule, similar in structure to the chromosome of prokaryotes, and many small ribosomes on which protein synthesis occurs, partially independent of the nucleus. Plastids can change from one type to another (chloroplasts to chromoplasts and leucoplasts); they are semi-autonomous organelles of the cell. The increase in the number of plastids occurs due to their division into two and budding, which is preceded by reduplication of the circular DNA molecule.

Non-membrane cell organelles

1. Ribosomes are round formations of two subunits, consisting of 50% RNA and 50% proteins. Subunits are formed in the nucleus, in the nucleolus, and in the cytoplasm in the presence of Ca 2+ ions they are combined into integral structures. In the cytoplasm, ribosomes are located on the membranes of the endoplasmic reticulum (granular ER) or freely. In the active center of ribosomes, the process of translation occurs (selection of tRNA anticodons to mRNA codons). Ribosomes, moving along the mRNA molecule from one end to the other, sequentially make the mRNA codons available for contact with the tRNA anticodons.

2. Centrioles (cell center) are cylindrical bodies, the wall of which is 9 triads of protein microtubules. In the cell center, centrioles are located at right angles to each other. They are capable of self-reproduction according to the principle of self-assembly. Self-assembly is the formation of structures similar to existing ones with the help of enzymes. Centrioles take part in the formation of spindle filaments. They ensure the process of chromosome segregation during cell division.

3. Flagella and cilia are organelles of movement; they have a single structural plan - the outer part of the flagellum faces the environment and is covered with a section of the cytoplasmic membrane. They are a cylinder: its wall is made up of 9 pairs of protein microtubules, and in the center there are two axial microtubules. At the base of the flagellum, located in the ectoplasm - the cytoplasm lying directly below the cell membrane, another short microtubule is added to each pair of microtubules. As a result, a basal body is formed, consisting of nine triads of microtubules.

4. The cytoskeleton is represented by a system of protein fibers and microtubules. Provides maintenance and change in the shape of the cell body and the formation of pseudopodia. Responsible for amoeboid movement, forms the internal framework of the cell, and ensures the movement of cellular structures throughout the cytoplasm.

Main groups of organelles. Organelles are permanent intracellular structures that have a specific structure and perform corresponding functions. Organelles are divided into two groups: membrane and non-membrane. Membrane organelles come in two varieties: double-membrane and single-membrane. The double-membrane components are plastids, mitochondria and the cell nucleus. Single-membrane organelles include the organelles of the vacuolar system - the endoplasmic reticulum, the Golgi complex, lysosomes, vacuoles of plant and fungal cells, pulsating vacuoles, etc. Non-membrane organelles include ribosomes and the cell center, which are constantly present in the cell. The expression of cytoskeletal elements (a permanent component of the cell) can change significantly during the cell cycle - from the complete disappearance of one component (for example, cytoplasmic tubes during cell division) to the appearance of new structures (division spindles).

A common property of membrane organelles is that they are all built from lipoprotein films (biological membranes), which close on themselves so that closed cavities, or compartments, are formed. The internal contents of these compartments are always different from the hyaloplasm.

Double membrane organelles. Double-membraned organelles include plastids and mitochondria. Plastids are characteristic organelles of cells of autotrophic eukaryotic organisms. Their color, shape and size are very diverse. There are chloroplasts, chromoplasts and leucoplasts.

Chloroplasts They have a green color due to the presence of the main pigment - chlorophyll. Chloroplasts also contain auxiliary pigments - carotenoids (orange). In shape, chloroplasts are oval lens-shaped bodies measuring (5-10) x (2-4) microns. One leaf cell can contain 15-20 or more chloroplasts, and some algae have only 1-2 giant chloroplasts (chromatophores) of various shapes.

Chloroplasts are bounded by two membranes - outer and inner (Fig. 1.8).

Rice. 1.8. Chloroplast structure diagram: I —outer membrane; 2 — ribosomes; 3 — plastoglobules; 4 - grains; 5 —thylakoids; 6 — matrix; 7 —DNA; 8 — internal membrane; 9 —intermembrane space.

The outer membrane delimits the liquid internal homogeneous environment of the chloroplast - the stroma (matrix). The stroma contains proteins, lipids, DNA (a circular molecule), RNA, ribosomes and storage substances (lipids, starch and protein grains) as well as enzymes involved in the fixation of carbon dioxide.

The inner membrane of the chloroplast forms invaginations into the stroma - thylakoids, or lamellae, which have the shape of flattened sacs (cisterns). Several such thylakoids lying on top of each other form a grana, in which case they are called thyl grana acoids. It is in the thylakoid membranes that light-sensitive pigments are localized, as well as electron and proton carriers that participate in the absorption and transformation of light energy.

Chloroplasts in the cell carry out the process of photosynthesis.

Leukoplasts- small colorless plastids of various shapes. They are spherical, ellipsoidal, dumbbell-shaped, cup-shaped, etc. Compared to chloroplasts, their internal membrane system is poorly developed.

Leukoplasts are mainly found in the cells of organs hidden from sunlight (roots, rhizomes, tubers, seeds). They carry out secondary synthesis and accumulation of reserve nutrients - starch, less often fats and proteins.

Chromoplasts differ from other plastids in their unique shape (disc-shaped, jagged, crescent-shaped, triangular, rum-

bic, etc.) and color (orange, yellow, red). Chromoplasts lack chlorophyll and are therefore incapable of photosynthesis. Their internal membrane structure is weakly expressed.

Chromoplasts are present in the cells of the petals of many plants (buttercups, marigolds, daffodils, dandelions, etc.), mature fruits (tomatoes, rowan, lily of the valley, rose hips) and root vegetables (carrots, beets), as well as leaves in the autumn. The bright color of these organs is due to various pigments belonging to the group of carginoids, which are concentrated in chromoplasts.

All types of plastids are genetically related to each other, and some types can transform into others:

Thus, the entire process of interconversion of plastids can be represented as a series of changes going in one direction - from proplastids to chromoplasts.

Mitochondria are integral components of all eukaryotic cells. They are granular or thread-like structures 0.5 µm thick and up to 7-10 µm long.

Mitochondria are bounded by two membranes - outer and inner (Fig. 1.9). Between the outer and inner membranes there is a so-called perimitochondriaal space, which is the site of accumulation of hydrogen ions H + Outer mitochondrial membrane separates it from the hyaloplasm. Inner membrane forms many invaginations into mitochondria - the so-called christ. Enzymes are located on the cristae membrane or inside it, including carriers of electrons and hydrogen ions H +, which are involved in oxygen respiration. The outer membrane is highly permeable and many compounds pass through it easily. The inner membrane is less permeable. The internal contents of the mitochondria limited by it (matrix) its composition is close to that of the cytoplasm. The matrix contains various proteins, V including enzymes, DNA (circular molecule), all types of RNA, amino acids, ribosomes, a number of vitamins. DNA provides some genetic autonomy to mitochondria, although in general their work is coordinated by nuclear DNA.

Rice. 1.9. Scheme of the structure of mitochondria: a - longitudinal section; 6 — three-dimensional structure diagram; 1 — outer membrane; 2— matrix; 3 —intermembrane space; 4 — granule; 5 —DNA; 6 — inner membrane; 7 — ribosomes.

The oxygen stage of cellular respiration occurs in mitochondria.

Single-membrane organelles. A huge number of different substances are synthesized in the cell. Some of them are consumed for their own needs (ATP synthesis, construction of organelles, accumulation of nutrients), some are removed from the cell and used to build the membrane (plant and fungal cells), glyco-calyx (animal cells). Cellular secretions also include enzymes, hormones, collagen, keratin, etc. The accumulation of these substances and their movement from one part of the cell to another or removal beyond its boundaries occurs in a system of closed cytoplasmic membranes - the endoplasmic reticulum, or endoplasmic reticulum, and the Golgi complex , making up the transport system of cells.

Endoplasmic reticulum was discovered using an electron microscope in 1945. It is a system of branched channels, cisterns (vacuoles), and vesicles that create a kind of loose network in the cytoplasm (Fig. 1.10). The walls of channels and cavities are formed by elementary membranes.

There are two types of endoplasmic reticulum in a cell: granular (rough) And agranular (smooth). The granular endoplasmic reticulum is densely studded with ribosomes, which carry out protein biosynthesis. Synthesized proteins pass through the membrane into the channels and cavities of the endoplasmic reticulum, are isolated from the cytoplasm, accumulate there, mature and move to other parts of the cell or to the Golgi complex in special membrane vesicles that are detached from the cisterns of the endoplasmic reticulum.

Rice. 1.10. Scheme of the structure of rough (1) and smooth (2) endoplasmic reticulum.

Functions of the endoplasmic reticulum the following:

1. In the membranes of the granular endoplasmic reticulum, proteins accumulate and are isolated, which, after their synthesis, could be harmful to the cell. For example, the synthesis of hydrolytic enzymes and their free release into the cytoplasm would lead to self-digestion of the cell and its death. However, this does not happen, because such proteins are reliably isolated in the cavities of the endoplasmic reticulum.
2. The ribosomes of the granular endoplasmic reticulum also synthesize integral and peripheral proteins of cell membranes and some of the proteins of the cytoplasm.
3. The cisternae of the rough endoplasmic reticulum are associated with the nuclear envelope, some of them being a direct continuation of the latter. It is believed that after cell division, the membranes of new nuclei are formed from the cisterns of the endoplasmic reticulum.
4. The processes of synthesis of lipids and some carbohydrates (for example, glycogen) take place on the membranes of the smooth endoplasmic reticulum.

Golgi complex (apparatus) discovered in 1898 by the Italian scientist C. Golgi. It is a system of flat disc-shaped closed tanks, which are located one above the other in the form of a stack and form dictyosome. Membranous tubes and vesicles extend from the tanks in all directions (Fig. 1.11). The number of dictyosomes in cells varies from one to several dozen depending on the type of cell and the phase of their development.

Fig 1.11. Scheme of the structure of the Golgi apparatus: 1 — bubbles; 2 — tanks.

Substances synthesized in the endoplasmic reticulum are delivered to the Golgi complex. Vesicles are detached from the cisterns of the endoplasmic reticulum and connect to the cisterns of the Golgi complex, where these substances are modified and mature.

Vesicles of the Golgi complex are involved in the formation of the cytoplasmic membrane and walls of plant cells after division, as well as in the formation of vacuoles and primary lysosomes.

Mature dictyosome cisternae release vesicles or Golgi vacuoles filled with secretion. The contents of such vesicles are either used by the cell itself or removed beyond its boundaries. In the latter case, Golgi vesicles approach the plasma membrane, connect with it and pour their contents out, and their membrane is included in the plasma membrane and thus its renewal occurs.

The Golgi complex cisterns actively extract monosaccharides from the cytoplasm and synthesize more complex oligo- and polysaccharides from them. In plants, as a result of this, pectin substances, hemicellulose and cellulose are formed, which are used to build the cell wall, and root cap mucus. In animals, glycoproteins and glycolipids of the glycocalyx are synthesized in a similar way, pancreatic secretions, salivary amylase, pituitary peptide hormones, and collagen are produced.

The Golgi complex is involved in the formation of lysosomes, milk proteins in the mammary glands, bile in the liver, lens substances, tooth enamel, and g.p.

The Golgi complex and the endoplasmic reticulum are closely related; their joint activity ensures the synthesis and transformation of substances in the cell, their isolation, accumulation and transport.

Lysosomes- these are membrane vesicles up to 2 microns in size. Lysosomes contain hydrolytic enzymes that can digest proteins, lipids, carbohydrates, and nucleic acids. Lysosomes are formed from vesicles that separate from the Golgi complex, and hydrolytic enzymes are first synthesized on the rough plasma reticulum.

Merging with endocytic vesicles, lysosomes form digestive vacuole (secondary lysosome), where organic substances are broken down into their constituent monomers. The latter enter the cell cytoplasm through the membrane of the digestive vacuole. This is exactly how, for example, the neutralization of bacteria in blood cells occurs - neutrophils.

Secondary lysosomes, in which the digestion process has completed, contain practically no enzymes. They contain only undigested residues, i.e., non-hydrolyzable material, which is either excreted outside the cell or accumulates in the cytoplasm.

The breakdown of foreign material received by endocytosis by lysosomes is called heterophagy. Lysosomes are also involved in the destruction of cell materials, such as reserve nutrients, as well as macromolecules and entire organelles that have lost their functional activity. (autophagy). With pathological changes in the cell or its aging, the membranes of lysosomes can be destroyed: enzymes enter the cytoplasm, and self-digestion of the cell occurs —autolysis. Sometimes, with the help of lysosomes, entire cell complexes and organs are destroyed. For example, when a tadpole turns into a frog, lysosomes located in the cells of the tail digest it: the tail disappears, and the substances formed during this process are absorbed and used by other cells of the body.

Vacuoles- large membrane vesicles or cavities in the cytoplasm filled with cell sap. Vacuoles are formed in plant and fungal cells from vesicle-like extensions of the endoplasmic reticulum or from vesicles of the Golgi complex. In the meristematic cells of plants, many small vacuoles first appear. As they grow larger, they merge into central vacuole which occupies up to 70-90% of the cell volume and can be penetrated by strands of cytoplasm (Fig. 1.12).

Rice. 1.12. Vacuole in a plant cell: 1 — vacuole; 2 — cytopasmatic cords; 3 — core; 4 — chloroplasts.

Contents of vacuoles - cell sap. It is an aqueous solution of various inorganic and organic substances. Most of them are products of protoplast metabolism, which can appear and disappear during different periods of cell life. The chemical composition and concentration of cell sap are very variable and depend on the plant type, organ, tissue and cell condition. Cell sap contains salts, sugars (primarily sucrose, glucose, fructose), organic acids (malic, citric, oxalic, acetic, etc.), amino acids, and proteins. These substances are intermediate metabolic products, temporarily removed from the cell's metabolism into the vacuole. They are spare cell substances.

In addition to reserve substances that can be reused in metabolism, cell sap contains phenols, tannins (tannins), alkaloids, and anthocyanins, which are excreted from metabolism into the vacuole and thus isolated from the cytoplasm.

Tannins are especially common in the cell sap (as well as in the cytoplasm and membranes) of cells in leaves, bark, wood, unripe fruits and seed coats. Alkaloids are present, for example, in coffee seeds (caffeine), poppy fruits (morphine) and henbane (atropine), stems and leaves of lupine (lupinine), etc. It is believed that tannins with their astringent taste, alkaloids and toxic polyphenols perform a protective function: their poisonous (usually bitter) taste and unpleasant odor repel herbivores, which prevents them from being eaten.

Vacuoles also often accumulate end products of cell activity. (waste). Such a substance for plant cells is calcium oxalate, which is deposited in vacuoles in the form of crystals of various shapes.

The cell sap of many plants contains pigments, giving the cell sap a variety of colors. Pigments determine the color of the corollas of flowers, fruits, buds and leaves, as well as the roots of some plants (for example, beets).

The cell sap of some plants contains physiologically active substances - phytohormones (growth regulators), phytoncides, enzymes. In the latter case, the vacuoles act as lysosomes. After cell death, the vacuole membrane loses selective permeability, and enzymes released from it cause autolysis of the cell.

Functions of vacuoles the following:

1. Vacuoles play a major role in the absorption of water by plant cells. Water by osmosis through its membrane enters the vacuole, the cell sap of which is more concentrated than the cytoplasm, and puts pressure on the cytoplasm, and therefore on the cell membrane. As a result, turgor pressure develops in the cell, which determines the relative rigidity of plant cells and causes cell elongation during their growth.
2. In the storage tissues of plants, instead of one central one, there are often several vacuoles in which reserve nutrients (fats, proteins) accumulate. Contractile (pulsating) vacuoles serve for osmotic regulation, primarily in freshwater protozoa, since water from the surrounding hypotonic solution continuously enters their cells by osmosis (the concentration of substances in river or lake water is much lower than the concentration of substances in protozoan cells). Contractile vacuoles absorb excess water and then expel it out through contractions.

Non-membrane organelles. Cellular center. The cells of most animals, as well as some fungi, algae, mosses and ferns, have centrioles. They are usually located in the center of the cell, which determines their name (Fig. 1.13).

Centrioles are hollow cylinders no more than 0.5 µm long. They are arranged in pairs perpendicular to one another (Fig. 1.14). Each centriole is made up of nine triplets of microtubules.

The main function of centrioles is to organize the microtubules of the cell division spindle.

Centrioles are identical in structure basal bodies, which are always found at the base of flagella and cilia. In all likelihood, basal bodies are formed by doubling centrioles. Basal bodies, like centrioles, are centers for organizing microtubules that make up flagella and cilia.

Flagella and cilia- organelles of movement in the cells of many species of living beings. They are mobile cytoplasmic processes that serve either for the movement of the entire organism (many bacteria, protozoa, ciliated worms) or reproductive cells (sperm, zoospores), or for the transport of particles and liquids (for example, cilia of ciliated cells of the mucous membrane of the nasal cavities and trachea , oviducts, etc.).

The flagella of eukaryotic cells contain 20 microtubules along their entire length: 9 peripheral doublets and 2 central single ones. At the base of the flagellum in the cytoplasm there is a basal body.

Flagella are about 100 µm or more in length. Short flagella (10-20 microns), of which there are many on one cell, are called eyelashes.

The sliding of microtubules that are part of the flagella or cilia causes them to beat, which ensures the movement of the cell or the advancement of particles.

Ribosomes- These are the smallest spherical granules with a diameter of 15-35 nm, which are the site of protein synthesis from amino acids. They are found in the cells of all organisms, including prokaryotic ones. Unlike other organelles of the cytoplasm (plastids, mitochondria, cell center, etc.), ribosomes are represented in a cell in a huge number: about 10 million of them are formed during the cell cycle.

Ribosomes contain many molecules of various proteins and several rRNA molecules. A complete working ribosome consists of two unequal subunits (Fig. 1.15). The small subunit is rod-shaped with several protrusions. The large sub-unit looks like a hemisphere with three protruding protrusions. When combined into a ribosome, the small subunit rests at one end on one of the protrusions of the large subunit. The small subunit contains one RNA molecule, and the large subunit contains three.

Rice. 1.15, Scheme of the structure of a ribosome: 1 — small subunit; 2 — mRNA; 3 — TRIC; 4 — amino acid; 5 — large subunit; b — endoplasmic reticulum membrane; 7 — synthesized polypeptide chain.

In the cytoplasm, tens of thousands of ribosomes are located freely (singly or in groups) or attached to the filaments of the microtrabecular system, the outer surface of the nuclear membrane and the endoplasmic reticulum. They are also found in mitochondria and chloroplasts.

During protein synthesis, the ribosome protects the synthesized protein from the destructive action of cellular enzymes. The mechanism of the protective effect is that part of the newly synthesized protein is located in the channel-like structure of the large subunit.

Source : ON THE. Lemeza L.V. Kamlyuk N.D. Lisov "A manual on biology for those entering universities"

Lesson type: combined.

Methods: verbal, visual, practical, problem-search.

Lesson Objectives

Educational: deepen students’ knowledge of the structure of eukaryotic cells, teach them to apply them in practical classes.

Developmental: improve students’ abilities to work with didactic material; develop students' thinking by offering tasks to compare prokaryotic and eukaryotic cells, plant cells and animal cells, identifying similar and distinctive features.

Equipment: poster “Structure of the cytoplasmic membrane”; task cards; handout (structure of a prokaryotic cell, a typical plant cell, structure of an animal cell).

Interdisciplinary connections: botany, zoology, human anatomy and physiology.

Lesson Plan

I. Organizational moment

Checking readiness for the lesson.
Checking the list of students.
Communicate the topic and objectives of the lesson.

II. Learning new material

Division of organisms into pro- and eukaryotes

The cells are extremely varied in shape: some are round in shape, others look like stars with many rays, others are elongated, etc. Cells also vary in size - from the smallest, difficult to distinguish in a light microscope, to perfectly visible to the naked eye (for example, the eggs of fish and frogs).

Any unfertilized egg, including the giant fossilized dinosaur eggs that are kept in paleontological museums, was also once living cells. However, if we talk about the main elements of the internal structure, all cells are similar to each other.

Prokaryotes (from lat. pro- before, earlier, instead of and Greek. karyon– nucleus) are organisms whose cells do not have a membrane-bound nucleus, i.e. all bacteria, including archaebacteria and cyanobacteria. The total number of prokaryotic species is about 6000. All the genetic information of a prokaryotic cell (genophore) is contained in a single circular DNA molecule. Mitochondria and chloroplasts are absent, and the functions of respiration or photosynthesis, which provide the cell with energy, are performed by the plasma membrane (Fig. 1). Prokaryotes reproduce without a pronounced sexual process by dividing in two. Prokaryotes are capable of carrying out a number of specific physiological processes: they fix molecular nitrogen, carry out lactic acid fermentation, decompose wood, and oxidize sulfur and iron.

After an introductory conversation, students review the structure of a prokaryotic cell, comparing the main structural features with the types of eukaryotic cells (Fig. 1).

Eukaryotes - these are higher organisms that have a clearly defined nucleus, which is separated from the cytoplasm by a membrane (karyomembrane). Eukaryotes include all higher animals and plants, as well as unicellular and multicellular algae, fungi and protozoa. Nuclear DNA in eukaryotes is contained in chromosomes. Eukaryotes have cellular organelles bounded by membranes.

Differences between eukaryotes and prokaryotes

– Eukaryotes have a real nucleus: the genetic apparatus of the eukaryotic cell is protected by a membrane similar to the membrane of the cell itself.
– Organelles included in the cytoplasm are surrounded by a membrane.

Structure of plant and animal cells

The cell of any organism is a system. It consists of three interconnected parts: shell, nucleus and cytoplasm.

In your studies of botany, zoology, and human anatomy, you have already become familiar with the structure of different types of cells. Let's briefly review this material.

Exercise 1. Based on Figure 2, determine which organisms and tissue types the cells numbered 1–12 correspond to. What determines their shape?

Structure and functions of organelles of plant and animal cells

Using Figures 3 and 4 and the Biology Dictionary and Textbook, students complete a table comparing animal and plant cells.

Table. Structure and functions of organelles of plant and animal cells

Cell organelles	Structure of organelles	Function	Presence of organelles in cells
			plants	animals
Chloroplast	It is a type of plastid	Colors plants green and allows photosynthesis to occur.
Leukoplast	The shell consists of two elementary membranes; internal, growing into the stroma, forms a few thylakoids	Synthesizes and accumulates starch, oils, proteins
Chromoplast	Plastids with yellow, orange and red colors, the color is due to pigments - carotenoids	Red, yellow color of autumn leaves, juicy fruits, etc.
	Occupies up to 90% of the volume of a mature cell, filled with cell sap	Maintaining turgor, accumulation of reserve substances and metabolic products, regulation of osmotic pressure, etc.
Microtubules	Composed of the protein tubulin, located near the plasma membrane	They participate in the deposition of cellulose on cell walls and the movement of various organelles in the cytoplasm. During cell division, microtubules form the basis of the spindle structure
Plasma membrane (PMM)	Consists of a lipid bilayer penetrated by proteins immersed at varying depths	Barrier, transport of substances, communication between cells
Smooth EPR	System of flat and branching tubes	Carries out the synthesis and release of lipids
Rough EPR	It got its name because of the many ribosomes located on its surface.	Protein synthesis, accumulation and transformation for release from the cell to the outside
	Surrounded by a double nuclear membrane with pores. The outer nuclear membrane forms a continuous structure with the ER membrane. Contains one or more nucleoli	Carrier of hereditary information, center for regulating cell activity
Cell wall	Consists of long cellulose molecules arranged in bundles called microfibrils	External frame, protective shell
Plasmodesmata	Tiny cytoplasmic channels that penetrate cell walls	Unite protoplasts of neighboring cells
Mitochondria		ATP synthesis (energy storage)
Golgi apparatus	Consists of a stack of flat sacs called cisternae, or dictyosomes	Synthesis of polysaccharides, formation of CPM and lysosomes
Lysosomes		Intracellular digestion
Ribosomes	Consist of two unequal subunits - large and small, into which they can dissociate	Site of protein biosynthesis
Cytoplasm	Consists of water with a large number of dissolved substances containing glucose, proteins and ions	It houses other cell organelles and carries out all processes of cellular metabolism.
Microfilaments	Fibers made from the protein actin, usually arranged in bundles near the surface of cells	Participate in cell motility and change in shape
Centrioles	May be part of the cell's mitotic apparatus. A diploid cell contains two pairs of centrioles	Participate in the process of cell division in animals; in zoospores of algae, mosses and protozoa they form basal bodies of cilia
Microvilli	Plasma membrane protrusions	They increase the outer surface of the cell; microvilli collectively form the cell border

conclusions

1. The cell wall, plastids and central vacuole are unique to plant cells.
2. Lysosomes, centrioles, microvilli are present mainly only in the cells of animal organisms.
3. All other organelles are characteristic of both plant and animal cells.

Cell membrane structure

The cell membrane is located outside the cell, separating the latter from the external or internal environment of the body. Its basis is the plasmalemma (cell membrane) and the carbohydrate-protein component.

Functions of the cell membrane:

– maintains the shape of the cell and gives mechanical strength to the cell and the body as a whole;
– protects the cell from mechanical damage and the entry of harmful compounds into it;
– carries out recognition of molecular signals;
– regulates the metabolism between the cell and the environment;
– carries out intercellular interaction in a multicellular organism.

Cell wall function:

– represents an external frame – a protective shell;
– ensures the transport of substances (water, salts, and molecules of many organic substances pass through the cell wall).

The outer layer of animal cells, unlike the cell walls of plants, is very thin and elastic. It is not visible under a light microscope and consists of a variety of polysaccharides and proteins. The surface layer of animal cells is called glycocalyx, performs the function of direct connection of animal cells with the external environment, with all the substances surrounding it, but does not play a supporting role.

Under the glycocalyx of the animal cell and the cell wall of the plant cell there is a plasma membrane bordering directly on the cytoplasm. The plasma membrane consists of proteins and lipids. They are arranged in an orderly manner due to various chemical interactions with each other. Lipid molecules in the plasma membrane are arranged in two rows and form a continuous lipid bilayer. Protein molecules do not form a continuous layer; they are located in the lipid layer, plunging into it to different depths. Molecules of proteins and lipids are mobile.

Functions of the plasma membrane:

– forms a barrier separating the internal contents of the cell from the external environment;
– provides transport of substances;
– provides communication between cells in the tissues of multicellular organisms.

Entry of substances into the cell

The surface of the cell is not continuous. In the cytoplasmic membrane there are numerous tiny holes - pores, through which, with or without the help of special proteins, ions and small molecules can penetrate into the cell. In addition, some ions and small molecules can enter the cell directly through the membrane. The entry of the most important ions and molecules into the cell is not passive diffusion, but active transport, requiring energy expenditure. The transport of substances is selective. Selective permeability of the cell membrane is called semi-permeability.

By phagocytosis Large molecules of organic substances, such as proteins, polysaccharides, food particles, and bacteria enter the cell. Phagocytosis occurs with the participation of the plasma membrane. At the point where the surface of the cell comes into contact with a particle of any dense substance, the membrane bends, forms a depression and surrounds the particle, which is immersed inside the cell in a “membrane capsule”. A digestive vacuole is formed, and organic substances entering the cell are digested in it.

Amoebas, ciliates, and leukocytes of animals and humans feed by phagocytosis. Leukocytes absorb bacteria, as well as a variety of solid particles that accidentally enter the body, thus protecting it from pathogenic bacteria. The cell wall of plants, bacteria and blue-green algae prevents phagocytosis, and therefore this route of entry of substances into the cell is not realized in them.

Drops of liquid containing various substances in a dissolved and suspended state also penetrate into the cell through the plasma membrane. This phenomenon was called pinocytosis. The process of fluid absorption is similar to phagocytosis. A drop of liquid is immersed in the cytoplasm in a “membrane package”. Organic substances that enter the cell along with water begin to be digested under the influence of enzymes contained in the cytoplasm. Pinocytosis is widespread in nature and is carried out by cells of all animals.

III. Reinforcing the material learned

What two large groups are all organisms divided into based on the structure of their nucleus?
Which organelles are characteristic only of plant cells?
Which organelles are unique to animal cells?
How does the structure of the cell membrane of plants and animals differ?
What are the two ways substances enter a cell?
What is the significance of phagocytosis for animals?