The science that studies the structure and function of cells is called cytology.
Cell- an elementary structural and functional unit of the living.
Cells, despite their small size, are very complex. The internal semi-liquid content of the cell is called cytoplasm.
The cytoplasm is the internal environment of the cell, where various processes take place and the components of the cell - organelles (organelles) - are located.
Cell nucleus
The cell nucleus is the most important part of the cell.
The nucleus is separated from the cytoplasm by a membrane consisting of two membranes. There are numerous pores in the shell of the nucleus so that various substances can get from the cytoplasm into the nucleus, and vice versa.
The internal contents of the core are called karyoplasm or nuclear juice... The nuclear juice contains chromatin and nucleolus.
Chromatin is a strand of DNA. If the cell begins to divide, the chromatin threads are tightly wound in a spiral onto special proteins, like threads on a spool. Such dense formations are clearly visible under a microscope and are called chromosomes.
Core contains genetic information and controls the life of the cell.
Nucleolus is a dense rounded body inside the nucleus. Usually, there are from one to seven nucleoli in the cell nucleus. They are clearly visible between cell divisions, and during division they are destroyed.
The function of the nucleoli is the synthesis of RNA and proteins, from which special organelles are formed - ribosomes.
Ribosomes participate in protein biosynthesis. In the cytoplasm, ribosomes are most often located on rough endoplasmic reticulum... Less commonly, they are freely suspended in the cytoplasm of the cell.
Endoplasmic reticulum (EPS) participates in the synthesis of cell proteins and the transport of substances inside the cell.
A significant part of the substances synthesized by the cell (proteins, fats, carbohydrates) is not consumed immediately, but through the EPS channels it enters for storage into special cavities, stacked in peculiar piles, “cisterns,” and separated from the cytoplasm by a membrane. These cavities are called Golgi apparatus (complex)... Most often, the cisterns of the Golgi apparatus are located near the cell nucleus.
Golgi apparatus takes part in the transformation of cell proteins and synthesizes lysosomes- the digestive organelles of the cell.
Lysosomes are digestive enzymes, “packaged” in membrane vesicles, bud off and spread through the cytoplasm.
The Golgi complex also accumulates substances that the cell synthesizes for the needs of the whole organism and which are removed from the cell to the outside.
Mitochondria- energy organelles of cells. They convert nutrients into energy (ATP) and take part in cell respiration.
Mitochondria are covered with two membranes: the outer membrane is smooth, and the inner one has numerous folds and protrusions - cristae.
Plasma membrane
For a cell to be a single system, it is necessary that all its parts (cytoplasm, nucleus, organelles) are held together. For this, in the process of evolution, the plasma membrane, which, surrounding each cell, separates it from the external environment. The outer membrane protects the internal contents of the cell - the cytoplasm and the nucleus - from damage, maintains the constant shape of the cell, ensures the communication of cells with each other, selectively passes the necessary substances into the cell and removes metabolic products from the cell.
The structure of the membrane is the same for all cells. The membrane is based on a double layer of lipid molecules, in which numerous protein molecules are located. Some proteins are located on the surface of the lipid layer, while others penetrate both lipid layers through and through.
Special proteins form the thinnest channels through which ions of potassium, sodium, calcium and some other ions with a small diameter can pass into the cell or from it. However, larger particles (molecules of food substances - proteins, carbohydrates, lipids) cannot pass through the membrane channels and enter the cell using phagocytosis or pinocytosis:
- In the place where the food particle touches the outer membrane of the cell, an invagination is formed, and the particle enters the cell, surrounded by the membrane. This process is called phagocytosis (plant cells on top of the outer cell membrane are covered with a dense layer of fiber (cell membrane) and cannot capture substances through phagocytosis).
- Pinocytosis differs from phagocytosis only in that in this case the invagination of the outer membrane captures not solid particles, but droplets of liquid with substances dissolved in it. This is one of the main mechanisms for the penetration of substances into the cell.
All living things and organisms do not consist of cells: plants, fungi, bacteria, animals, people. Despite the minimal size, the cell performs all the functions of the whole organism. Complex processes take place inside it, on which the vitality of the body and the work of its organs depend.
In contact with
Structural features
Scientists are studying structural features of the cell and the principles of its work. It is possible to examine in detail the features of the cell structure only with the help of a powerful microscope.
All our tissues - skin, bones, internal organs consist of cells that are from building material, come in different shapes and sizes, each variety performs a specific function, but the main features of their structure are similar.
First, let's find out what lies behind structural organization of cells... In the course of the research, scientists have established that the cellular foundation is membrane principle. It turns out that all cells are formed of membranes, which consist of a double layer of phospholipids, where protein molecules are immersed from the outside and inside.
What property is characteristic for all types of cells: the same structure, as well as functionality - regulation of the metabolic process, the use of its own genetic material (presence and RNA), receipt and consumption of energy.
The structural organization of the cell is based on the following elements that perform a specific function:
- membrane- the cell membrane, consists of fats and proteins. Its main task is to separate the substances inside from the external environment. It has a semi-permeable structure: it is also capable of transmitting carbon monoxide;
- core- the central region and the main component, separated from other elements by a membrane. It is inside the nucleus that information about growth and development, genetic material, presented in the form of DNA molecules that make up the composition, is located;
- cytoplasm Is a liquid substance that forms an internal environment where a variety of vital processes take place, contains a lot of important components.
What does the cellular content consist of, what are the functions of the cytoplasm and its main components:
- Ribosome- the most important organoid, which is necessary for the processes of biosynthesis of proteins from amino acids, proteins perform a huge number of vital tasks.
- Mitochondria- another component located inside the cytoplasm. It can be described in one word combination - an energy source. Their function is to provide components with power for further energy production.
- Golgi apparatus consists of 5 - 8 bags, which are interconnected. The main task of this apparatus is to transfer proteins to other parts of the cell to provide energy potential.
- Cleaning of damaged elements is carried out lysosomes.
- Transportation is handled by endoplasmic reticulum, along which proteins move molecules of useful substances.
- Centrioli responsible for reproduction.
Core
Since it is a cell center, therefore, special attention should be paid to its structure and functions. This component is an essential element for all cells: it contains hereditary characteristics. Without the nucleus, the processes of reproduction and transmission of genetic information would become impossible. Take a look at the figure showing the structure of the nucleus.
- The nuclear envelope, which is highlighted in lilac color, lets the substances inside and releases them back through the pores - small holes.
- Plasma is a viscous substance, it contains all the other nuclear components.
- the core is located in the very center, has the shape of a sphere. Its main function is the formation of new ribosomes.
- If you look at the central part of the cell in section, you can see subtle blue weaves - chromatin, the main substance, which consists of a complex of proteins and long DNA strands that carry the necessary information.
Cell membrane
Let's take a closer look at the work, structure and function of this component. Below is a table that clearly shows the importance of the outer shell.
Chloroplasts
This is another overriding component. But why chloroplasts were not mentioned earlier, you may ask. Because this component is found only in plant cells. The main difference between animals and plants lies in the way of feeding: in animals it is heterotrophic, and in plants it is autotrophic. This means that animals are not able to create, that is, synthesize organic substances from inorganic ones - they feed on ready-made organic substances. Plants, on the other hand, are capable of carrying out the process of photosynthesis and contain special components - chloroplasts. These are green plastids containing chlorophyll. With its participation, the energy of light is converted into the energy of chemical bonds of organic substances.
Interesting! Chloroplasts in a large volume are concentrated mainly in the aerial part of plants - green fruits and leaves.
If you are asked the question: name an important feature of the structure of organic compounds of the cell, then the answer can be given as follows.
- many of them contain carbon atoms that have different chemical and physical properties, and are also capable of bonding with each other;
- are carriers, active participants in various processes occurring in organisms, or are their products. This refers to hormones, various enzymes, vitamins;
- can form chains and rings, which provides a variety of connections;
- destroyed by heating and interaction with oxygen;
- atoms in the composition of molecules combine with each other using covalent bonds, do not decompose into ions and therefore slowly interact, reactions between substances take a very long time - for several hours or even days.
Chloroplast structure
Fabrics
Cells can exist one at a time, as in unicellular organisms, but most often they combine into groups of their own kind and form various tissue structures that make up the organism. There are several types of tissues in the human body:
- epithelial- concentrated on the surface of the skin, organs, elements of the digestive tract and the respiratory system;
- muscular- we move thanks to the contraction of the muscles of our body, we carry out a variety of movements: from the simplest movement of the little finger to high-speed running. By the way, the heartbeat also occurs due to the contraction of muscle tissue;
- connective tissue makes up 80 percent of the mass of all organs and plays a protective and supporting role;
- nervous- forms nerve fibers. Thanks to her, various impulses pass through the body.
Reproduction process
Throughout the life of the body, mitosis occurs - this is the name of the division process, consisting of four stages:
- Prophase... Two centrioles of the cell divide and go in opposite directions. At the same time, the chromosomes form pairs, and the shell of the nucleus begins to break down.
- The second stage was named metaphases... Chromosomes are located between centrioles, gradually the outer shell of the nucleus completely disappears.
- Anaphase is the third stage, during which the centrioles continue to move in the opposite direction from each other, and individual chromosomes also follow the centrioles and move away from each other. The cytoplasm and the entire cell begin to shrink.
- Telophase- the final stage. The cytoplasm contracts until two identical new cells appear. A new membrane is formed around the chromosomes and one pair of centrioles appears in each new cell.
Interesting! Cells in the epithelium divide faster than in bone tissue. It all depends on the density of the fabrics and other characteristics. The average life span of the main structural units is 10 days.
Cell structure. The structure and function of the cell. Cell life.
Conclusion
You have learned what is the structure of the cell - the most important component of the body. Billions of cells make up an amazingly wisely organized system that ensures the efficiency and functioning of all representatives of the animal and plant world.
As a rule, a eukaryotic cell has one nucleus, but there are binucleated (ciliates) and multinucleated cells (opaline). Some highly specialized cells lose their nucleus for the second time (erythrocytes of mammals, sieve tubes of angiosperms).
The shape of the nucleus is spherical, elliptical, less often lobed, bean-shaped, etc. The diameter of the nucleus is usually from 3 to 10 microns.
Nucleus structure:
1 - outer membrane; 2 - inner membrane; 3 - pores; 4 - nucleolus; 5 - heterochromatin; 6 - euchromatin.
The nucleus is delimited from the cytoplasm by two membranes (each of them has a typical structure). Between the membranes there is a narrow gap filled with a semi-liquid substance. In some places, the membranes merge with each other, forming pores (3), through which the exchange of substances between the nucleus and the cytoplasm takes place. The outer nuclear (1) membrane from the side facing the cytoplasm is covered with ribosomes, which give it roughness, the inner (2) membrane is smooth. Nuclear membranes are part of the cell membrane system: the outgrowths of the outer nuclear membrane are connected to the channels of the endoplasmic reticulum, forming a single system of communicating channels.
Karyoplasm (nuclear juice, nucleoplasm) is the inner content of the nucleus, in which chromatin and one or more nucleoli are located. The composition of nuclear juice includes various proteins (including enzymes of the nucleus), free nucleotides.
The nucleolus (4) is a rounded dense body immersed in nuclear juice. The number of nucleoli depends on the functional state of the nucleus and varies from 1 to 7 or more. Nucleoli are found only in non-dividing nuclei; during mitosis, they disappear. The nucleolus is formed on certain parts of the chromosomes that carry information about the structure of rRNA. Such regions are called the nucleolar organizer and contain numerous copies of the genes encoding rRNA. Ribosome subunits are formed from rRNA and proteins coming from the cytoplasm. Thus, the nucleolus is an accumulation of rRNA and ribosomal subunits at different stages of their formation.
Chromatin is the internal nucleoprotein structures of the nucleus, stained with some dyes and differing in shape from the nucleolus. Chromatin is in the form of lumps, granules and filaments. The chemical composition of chromatin: 1) DNA (30–45%), 2) histone proteins (30–50%), 3) non-histone proteins (4–33%), therefore, chromatin is a deoxyribonucleoprotein complex (DNP). Depending on the functional state of chromatin, they are distinguished: heterochromatin (5) and euchromatin (6). Euchromatin is genetically active, heterochromatin is genetically inactive regions of chromatin. Euchromatin under light microscopy is indistinguishable, weakly stained and represents decondensed (despiralized, untwisted) areas of chromatin. Heterochromatin under a light microscope looks like lumps or granules, intensely stains and represents condensed (spiralized, compacted) areas of chromatin. Chromatin is a form of existence of genetic material in interphase cells. During cell division (mitosis, meiosis), chromatin is converted into chromosomes.
1. Review Figure 24 on p. 54-55 of the textbook. Remember the names, locations and functioning of the organelles.
2. Fill in the cluster "The main components of a eukaryotic cell".
3. On the basis of what basic characteristics is a cell considered eukaryotic?
Eukaryotic cells have a well-formed nucleus. Eukaryotic cells are large, complex in structure in comparison with prokaryotic cells.
4. Sketch the structure of the cell membrane and sign its elements.
5. Label the animal and plant cells in the drawing and indicate their main organelles.
6. Fill in the cluster "Basic functions of the outer cell membrane".
Membrane functions:
Barrier
Transport
Interaction of the cell with the environment and other cells.
7. Make up syncwine to the term "membrane".
Membrane.
Selectively permeable, two-layer.
It transports, protects, signals.
An elastic molecular structure composed of proteins and lipids.
Shell.
8. Why are the phenomena of phagocytosis and pinocytosis very common in animal cells and practically absent in plant and fungal cells?
In the cells of plants and fungi, there is a cell wall that animals do not have. This allows the cytoplasmic membrane to absorb water with mineral salts (pinocytosis) due to its greater elasticity. Due to this property, the process of phagocytosis is carried out - the capture of solid particles.
9. Fill in the cluster "Eukaryotic cell organelles".
Organoids: membrane and non-membrane.
Membrane: single membrane and double membrane.
10. Establish a correspondence between groups and individual organelles.
Organelles
1. Mitochondria
2. EPS
3. Cell center
4. Vacuole
5. Golgi apparatus
6. Lysosomes
7. Ribosomes
8. Plastids
Groups
A. Single membrane
B. Double membrane
B. Non-membrane
11. Complete the table.
The structure and function of cell organelles
12. Fill in the table.
COMPARATIVE CHARACTERISTICS OF PLANT AND ANIMAL CELLS
13. Choose the name of any organoid and make up three types of sentences with this term: declarative, interrogative, exclamatory.
The vacuole is a large membrane vesicle filled with cell sap.
Vacuole is a mandatory accessory of the plant cell!
What functions, besides the accumulation of reserve substances, does the vacuole perform?
14. Give definitions of concepts.
Inclusions- these are optional components of the cell that appear and disappear depending on the intensity and nature of metabolism in the cell and on the conditions of existence of the organism.
Organelles- permanent specialized structures in the cells of living organisms.
15. Choose the correct answer.
Test 1.
Responsible for the formation of lysosomes, the accumulation, modification and removal of substances from the cell:
2) the Golgi complex;
Test 2.
The hydrophobic basis of the cell membrane is made up of:
3) phospholipids;
Test 3.
Single-membrane cell organelles:
2) lysosomes;
16. Explain the origin and general meaning of the word (term), based on the meaning of the roots that make it up.
17. Select a term and explain how its modern meaning matches the original meaning of its roots.
The term chosen is exocytosis.
Compliance, the term corresponds, but the mechanism has become clear and refined. It is a cellular process in which membrane vesicles fuse with the outer cell membrane. During exocytosis, the contents of the secretory vesicles are released to the outside, and their membrane merges with the cell membrane.
18. Formulate and write down the main ideas § 2.7.
The cell consists of three main components: the nucleus, the cytoplasm, and the cell membrane.
The cytoplasm contains organelles, inclusions, and hyaloplasm (main substance). Organoids are single-membrane (EPS, Golgi complex, lysosomes, etc.), two-membrane (mitochondria, plastids) and non-membrane (ribosomes, cell center). A plant cell differs from an animal cell in that it has additional structures: vacuole, plastids, cell wall, and there are no centrioles in the cell center. All organelles and cell components make up a well-coordinated complex that works as a whole.
Organelles – permanent and obligatory components of cells; specialized sections of the cytoplasm of the cell, which have a specific structure and perform specific functions in the cell. Distinguish between general and special purpose organelles.
General purpose organelles are found in most cells (endoplasmic reticulum, mitochondria, plastids, Golgi complex, lysosomes, vacuoles, cell center, ribosomes). Special purpose organelles are characteristic only of specialized cells (myofibrils, flagella, cilia, contractile and digestive vacuoles). Organoids (with the exception of ribosomes and the cell center) have a membrane structure.
Endoplasmic reticulum (ER) – it is a branched system of interconnected cavities, tubes and channels formed by elementary membranes and permeating the entire thickness of the cell. Opened in 1943 by Porter. There are especially many channels of the endoplasmic reticulum in cells with intensive metabolism. On average, the EPS volume ranges from 30% to 50% of the total cell volume. EPS is labile. The shape of the inner lacunae and kana
fishing, their size, location in the cage and the number change in the process of life. The cage is more developed in animals. EPS is morphologically and functionally connected with the boundary layer of the cytoplasm, the nuclear envelope, ribosomes, the Golgi complex, vacuoles, forming together with them a single functional-structural system for the metabolism and energy and movement of substances inside the cell. Mitochondria and plastids accumulate near the endoplasmic reticulum.
There are two types of EPS: rough and smooth. Enzymes of fat and carbohydrate synthesis systems are localized on the membranes of smooth (agranular) EPS: the synthesis of carbohydrates and almost all cellular lipids occurs here. Membranes of a smooth variety of the endoplasmic reticulum predominate in the cells of the sebaceous glands, liver (glycogen synthesis), in cells with a high content of nutrients (plant seeds). On the membrane of rough (granular) EPS, ribosomes are located, where the biosynthesis of proteins is carried out. Some of the proteins they synthesize are included in the membrane of the endoplasmic reticulum, the rest enter the lumen of its channels, where they are converted and transported to the Golgi complex. There are especially many rough membranes in glandular cells and nerve cells.
Rice. Rough and smooth endoplasmic reticulum.
Rice. Transport of substances through the system nucleus - endoplasmic reticulum (EPR) - Golgi complex.
Functions of the endoplasmic reticulum:
1) synthesis of proteins (rough EPS), carbohydrates and lipids (smooth EPS);
2) transport of substances, both entering the cell and newly synthesized;
3) division of the cytoplasm into compartments (compartments), which provides the spatial separation of enzyme systems necessary for their sequential entry into biochemical reactions.
Mitochondria - are present in almost all types of cells of single and multicellular organisms (with the exception of mammalian erythrocytes). Their number in different cells varies and depends on the level of functional activity of the cell. In the rat liver cell there are about 2500, and in the male reproductive cell of some mollusks - 20 - 22. There are more of them in the pectoral muscle of flying birds than in the pectoral muscle of flightless birds.
Mitochondria are spherical, oval, and cylindrical. Sizes are 0.2 - 1.0 microns in diameter and up to 5 - 7 microns in length.
Rice. Mitochondria.
The length of the filamentous forms reaches 15-20 microns. Outside, mitochondria are bounded by a smooth outer membrane, similar in composition to the plasmalemma. The inner membrane forms numerous outgrowths - cristae - and contains numerous enzymes, ATP-soms (mushroom bodies), which are involved in the transformation of nutrient energy into ATP energy. The number of cristae depends on the function of the cell. There are a lot of cristae muscles in the mitochondria; they occupy the entire internal cavity of the organoid. In the mitochondria of embryonic cells, cristae are rare. In plant outgrowths of the inner membrane, they are more often tubular. The mitochondrial cavity is filled with a matrix that contains water, mineral salts, enzyme proteins, and amino acids. Mitochondria have an autonomous protein-synthesizing system: a circular DNA molecule, various types of RNA, and smaller ribosomes than in the cytoplasm.
Mitochondria are closely connected by membranes of the endoplasmic reticulum, which channels often open directly into the mitochondria. With an increase in the load on the organ and the intensification of synthetic processes that require energy expenditure, contacts between EPS and mitochondria become especially numerous. The number of mitochondria can rapidly increase through division. The ability of mitochondria to reproduce is due to the presence in them of a DNA molecule that resembles the circular chromosome of bacteria.
Mitochondrial functions:
1) synthesis of a universal energy source - ATP;
2) the synthesis of steroid hormones;
3) biosynthesis of specific proteins.
Plastids - organelles of membrane structure, characteristic only for plant cells. The processes of synthesis of carbohydrates, proteins and fats take place in them. According to the content of pigments, they are divided into three groups: chloroplasts, chromoplasts and leukoplasts.
Chloroplasts have a relatively constant elliptical or lenticular shape. The largest diameter is 4-10 microns. The number in a cell ranges from a few units to several tens. Their size, color intensity, number and location in the cell depend on the lighting conditions, the type and physiological state of the plants.
Rice. Chloroplast, structure.
These are protein-lipoid bodies, consisting of 35-55% protein, 20-30% lipids, 9% chlorophyll, 4-5% carotenoids, 2-4% nucleic acids. The amount of carbohydrates varies; discovered a certain amount of mineral substances Chlorophyll - an ester of organic dibasic acid - chlorophyllin and organic alcohols - methyl (CH 3 OH) and phytol (C 20 H 39 OH). In higher plants, chloroplasts constantly contain chlorophyll a - it has a blue-green color, and chlorophyll b - yellow-green; and the chlorophyll content is several times higher.
In addition to chlorophyll, the composition of chloroplasts includes pigments - carotene C 40 H 56 and xanthophyll C 40 H 56 O 2 and some other pigments (carotenoids). In the green leaf, the yellow satellites of chlorophyll are masked by a brighter green color. However, in autumn, with leaf fall, in most plants, chlorophyll is destroyed and then the presence of carotenoid in the leaf is found - the leaf turns yellow.
Chloroplast is clad with a double shell, consisting of an outer and an inner membrane. The internal content - the stroma - has a lamellar (lamellar) structure. In the colorless stroma, granules are distinguished - green colored bodies, 0.3 - 1.7 microns. They are a collection of thylakoids - closed bodies in the form of flat vesicles or disks of membrane origin. Chlorophyll in the form of a monomolecular layer is located between the protein and lipid layers in close connection with them. The spatial arrangement of pigment molecules in the membrane structures of chloroplasts is very expedient and creates optimal conditions for the most efficient absorption, transfer and use of radiant energy. Lipids form anhydrous dielectric layers of chloroplast membranes, which are necessary for the functioning of the electron transport chain. Proteins (cytochromes, plastoquinones, ferredoxin, plastocyanin) and individual chemical elements - iron, manganese, etc. play the role of links in the electron transport chain. The number of grains in the chloroplast is from 20 to 200. Between the grains, linking them to each other, stromal lamellae are located. Gran lamellae and stromal lamellae have a membrane structure.
The internal structure of the chloroplast makes possible the spatial separation of numerous and varied reactions, which in their totality make up the content of photosynthesis.
Chloroplasts, like mitochondria, contain specific RNA and DNA, as well as smaller ribosomes and the entire molecular arsenal required for protein biosynthesis. These organelles have a sufficient amount of i-RNA to ensure the maximum activity of the protein-synthesizing system. However, they also contain enough DNA to encode certain proteins. They reproduce by division, by a simple constriction.
It has been established that chloroplasts can change their shape, size and position in the cell, that is, they are able to move independently (taxis of chloroplasts). In them, two types of contractile proteins were found, due to which, apparently, the active movement of these organelles in the cytoplasm is carried out.
Chromoplasts are widespread in the generative organs of plants. They color the petals of flowers (buttercup, dahlia, sunflower), fruits (tomatoes, mountain ash, rose hips) yellow, orange, red. In vegetative organs, chromoplasts are much less common.
Coloring of chromoplasts is due to the presence of carotenoids - carotene, xanthophyll and lycopene, which are in different states in plastids: in the form of crystals, lipoid solution or in combination with proteins.
Chromoplasts, in comparison with chloroplasts, have a simpler structure - they lack a lamellar structure. The chemical composition is also different: pigments - 20-50%, lipids up to 50%, proteins - about 20%, RNA - 2-3%. This indicates a lower physiological activity of chloroplasts.
Leukoplasts do not contain pigments, they are colorless. These smallest plastids are round, ovoid, or rod-shaped. In a cell, they are often grouped around the nucleus.
Internally, the structure is even less differentiated compared to chloroplasts. They synthesize starch, fats, proteins. In accordance with this, three types of leukoplasts are distinguished - amyloplasts (starch), oleoplasts (vegetable oils) and proteoplasts (proteins).
Leukoplasts arise from proplastids, with which they are similar in shape and structure, but differ only in size.
All plastids are genetically related to each other. They are formed from proplastids - the smallest colorless cytoplasmic formations, similar in appearance to mitochondria. Proplastids are found in spores, eggs, and embryonic growth points. Chloroplasts (in the light) and leukoplasts (in the dark) are formed directly from proplastids, and from them chromoplasts develop, which are the final product in the evolution of plastids in the cell.
Golgi complex - was first discovered in 1898 by the Italian scientist Golgi in animal cells. This is a system of internal cavities, cisterns (5-20), located close and parallel to each other, and large and small vacuoles. All these formations have a membrane structure and are specialized sections of the endoplasmic reticulum. The Golgi complex is better developed in animal cells than in plant cells; in the latter, it is called dictyosomes.
Rice. The structure of the Golgi complex.
The proteins and lipids that enter the lamellar complex undergo various transformations, accumulate, sorted, packed into secretory vesicles and transported to their destination: to various structures inside the cell or outside the cell. Golgi complex membranes also synthesize polysaccharides and form lysosomes. In the cells of the mammary glands, the Golgi complex is involved in the formation of milk, and in the cells of the liver, bile.
Functions of the Golgi complex:
1) concentration, dehydration and compaction of proteins, fats, polysaccharides and substances synthesized in the cell from outside;
2) assembly of complex complexes of organic substances and their preparation for removal from the cell (cellulose and hemicellulose in plants, glycoproteins and glycolipids in animals);
3) the synthesis of polysaccharides;
4) the formation of primary lysosomes.
Lysosomes - small oval bodies with a diameter of 0.2-2.0 microns. The central position is occupied by a vacuole containing 40 (according to various sources 30-60) hydrolytic enzymes capable of cleaving proteins, nucleic acids, polysaccharides, lipids and other substances in an acidic medium (pH 4.5-5).
Around this cavity is the stroma, dressed from the outside with an elementary membrane. The breakdown of substances by enzymes is called lysis, which is why the organoid is called the lysosome. Lysosomes are formed in the Golgi complex. Primary lysosomes approach directly to pinocytic or phagocytic vacuoles (endosomes) and pour out their contents into their cavity, forming secondary lysosomes (phagosomes), inside of which substances are digested. The lysis products enter the cytoplasm through the lysosomal membrane and are included in further metabolism. Secondary lysosomes with residues of undigested substances are called residual bodies. An example of secondary lysosomes are the digestive vacuoles of protozoa.
Functions of lysosomes:
1) intracellular digestion of food macromolecules and foreign components entering the cell during pino- and phagocytosis, providing the cell with additional raw materials for biochemical and energy processes;
2) during starvation, lysosomes digest some organelles and replenish the supply of nutrients for some time;
3) destruction of the temporary organs of embryos and larvae (the tail and gills of the frog) in the process of postembryonic development;
Rice. Lysosome formation
Vacuoles – cavities in the cytoplasm of plant cells and protist, filled with liquid. They are in the form of bubbles, thin tubules and others. Vacuoles are formed from the extensions of the endoplasmic reticulum and the vesicles of the Golgi complex as the thinnest cavities, then, as the cell grows and the accumulation of metabolic products, their volume increases, and the number decreases. A developed, formed cell usually has one large vacuole, which occupies a central position.
The vacuoles of plant cells are filled with cell sap, which is an aqueous solution of organic (malic, oxalic, citric acids, sugar, inulin, amino acids, proteins, tannins, alkaloids, glucosides) and mineral (nitrates, chlorides, phosphates) substances.
In protists, there are digestive and contractile vacuoles.
Vacuole functions:
1) storage of reserve nutrients and reservoirs of excretions (in plants);
2) determine and maintain osmotic pressure in cells;
3) provide intracellular digestion in protists.
Rice. Cell center.
Cell center usually located near the nucleus and consists of two centrioles located perpendicular to each other and surrounded by a radiant sphere. Each centriole is a hollow cylindrical body 0.3-0.5 μm long and 0.15 μm long, the wall of which is formed by 9 triplets of microtubules. If the centriole lies at the base of the cilium or flagellum, then it is called basal body.
Before division, centrioles diverge to opposite poles and a daughter centriole appears near each of them. From centrioles located at different poles of the cell, microtubules are formed, growing towards each other. They form a mitotic spindle, which contributes to the even distribution of genetic material between daughter cells, and are the center of the cytoskeleton organization. Some of the spindle filaments are attached to the chromosomes. In the cells of higher plants, the cell center has no centrioles.
Centrioles are self-replicating organelles of the cytoplasm. They arise as a result of duplication of existing ones. This occurs when the centrioles diverge. Immature centriole contains 9 single microtubules; Apparently, each microtubule is a matrix for the assembly of triplets characteristic of a mature centriole.
The centrosome is characteristic of animal cells, some fungi, algae, mosses and ferns.
Cell center functions:
1) the formation of fission poles and the formation of fission spindle microtubules.
Ribosomes - small spherical organelles, from 15 to 35 nm. They consist of two subunits large (60S) and small (40S). They contain about 60% protein and 40% ribosomal RNA. The rRNA molecules form its structural framework. Most proteins are specifically associated with certain regions of rRNA. Some proteins are included in the ribosome only during protein biosynthesis. Ribosome subunits are formed in the nucleoli. and through the pores in the nuclear envelope enter the cytoplasm, where they are located either on the EPA membrane, or on the outer side of the nuclear envelope, or freely in the cytoplasm. First, rRNA is synthesized on the nucleolar DNA, which is then covered with ribosomal proteins coming from the cytoplasm, cleaved to the required size and forming ribosome subunits. There are no fully formed ribosomes in the nucleus. The union of subunits into a whole ribosome occurs in the cytoplasm, usually during protein biosynthesis. Compared to mitochondria, plastids, prokaryotic cells, ribosomes in the cytoplasm of eukaryotic cells are larger. 5-70 units can be combined into polysomes.
Functions of ribosomes:
1) participation in protein biosynthesis.
Rice. 287. Ribosome: 1 - small subunit; 2 is a large subunit.
Cilia, flagella – outgrowths of the cytoplasm, covered with an elementary membrane, under which there are 20 microtubules forming 9 pairs along the periphery and two single ones in the center. Basal bodies are located at the base of the cilia and flagella. The length of the flagella reaches 100 microns. Cilia are short - 10-20 microns - flagella. The movement of the flagella is helical, and the cilia is paddle-like. Thanks to cilia and flagella, bacteria, protists, ciliary cells move, particles or liquids (cilia of the ciliated epithelium of the respiratory tract, oviducts), sex cells (spermatozoa) move.
Rice. The structure of eukaryotic flagella and cilia
Inclusions - temporary components of the cytoplasm, now emerging, then disappearing. As a rule, they are contained in cells at certain stages of the life cycle. The specificity of inclusions depends on the specificity of the corresponding tissue and organ cells. Inclusions are found mainly in plant cells. They can occur in the hyaloplasm, various organelles, less often in the cell wall.
In functional terms, inclusions are either compounds temporarily removed from the metabolism of cells (reserve substances - starch grains, lipid drops and protein deposits), or end products of metabolism (crystals of some substances).
Starch grains... These are the most common plant cell inclusions. Starch is stored in plants exclusively in the form of starch grains. They are formed only in the plastid stroma of living cells. In the process of photosynthesis, green leaves are formed assimilation, or primary starch. Assimilatory starch does not accumulate in the leaves and, being rapidly hydrolyzed to sugars, flows out into the parts of the plant in which it accumulates. There it again turns into starch, which is called secondary. Secondary starch is also formed directly in tubers, rhizomes, seeds, that is, where it is deposited in stock. Then they call him spare... Leukoplasts that accumulate starch are called amyloplasts... Especially rich in starch are seeds, underground shoots (tubers, bulbs, rhizomes), parenchyma of conductive tissues of roots and stems of woody plants.
Lipid drops... Found in almost all plant cells. The richest in them are seeds and fruits. Fatty oils in the form of lipid droplets are the second most important (after starch) form of reserve nutrients. The seeds of some plants (sunflower, cotton, etc.) can accumulate up to 40% oil by dry matter.
Lipid drops usually accumulate directly in the hyaloplasm. They are spherical bodies, usually submicroscopic in size. Lipid drops can also accumulate in leukoplasts, which are called elaioplasts.
Protein inclusions are formed in various cell organelles in the form of amorphous or crystalline deposits of various shapes and structures. Most often, crystals can be found in the nucleus - in the nucleoplasm, sometimes in the perinuclear space, less often in the hyaloplasm, plastid stroma, in the dilatation of the EPR cisterns, peroxisome matrix and mitochondria. Both crystalline and amorphous protein inclusions are found in vacuoles. The largest amount of protein crystals are found in the storage cells of dry seeds in the form of the so-called aleurone 3 grains or protein bodies.
Storage proteins are synthesized by ribosomes during seed development and deposited in the vacuole. When the seeds ripen, accompanied by their dehydration, the protein vacuoles dry out and the protein crystallizes. As a result, in a mature dry seed, protein vacuoles are converted into protein bodies (aleurone grains).