In 1898, the Italian scientist Camillo Golgi discovered an important cell organelle, which was later named after him. The structure and functions of the Golgi complex are important for the normal functioning of the cell itself and the whole organism.
Structure
The Golgi apparatus is a system of membranes resembling concave stacks. Each stack is a kind of cistern, a pouch, a cavity formed by the fusion of two membranes. This is the structural unit of the organelle, which is called the dictyosome. In one organelle, the number of dictyosomes can vary from four to seven.
Rice. 1. Structure of the Golgi complex.
Tanks interact with each other through a system of tubes and bubbles. According to the structure and functional purpose, the Golgi apparatus is divided into three sections. Each section contains certain enzymes that are involved in the modification of substances that have entered the organelle. The process starts with the cis section. Short description each department is presented in the table "Structure and functions of the Golgi complex in the cell."
In the animal cell, the Golgi complex is located closer to the nucleus and often comes into contact with the rough endoplasmic reticulum (ER). In plant cells, cisterns are scattered throughout the cytoplasm.
Meaning
The organelle performs three important functions:
- transfer and transformation of proteins;
- formation and modification of polysaccharides and lipids;
- production of lysosomes.
The work of the Golgi complex is not fully understood by biologists. The main function of the organelle is the synthesis of secrets, which are subsequently transported outside. Most of the secretions are of protein origin, so the Golgi complex processes the primary, immature proteins separated from the EPS into ready-made secrets. The mechanism of this transformation and the features of the process of transporting proteins through all departments are not completely clear.
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The Golgi apparatus produces glycolipids - complex compounds formed by carbohydrates and fats. The basis of the substances are polysaccharides, to which fatty acid residues are attached. Glycolipids are part of the nervous tissues and cell membranes.
Rice. 2. Glycolipids.
The third important function is the production of lysosomes. They are also "made" from ER proteins. The Golgi apparatus forms primary lysosomes - organelles resembling a vesicle or vesicle. Outside, the lysosome is limited by a thin membrane, inside there are enzymes that break down organic substances that come from outside or are produced by the cell (waste products). Separated from the Golgi complex, primary lysosomes merge in the cytoplasm with solid or liquid substances, turning into secondary lysosomes that perform the function of digestion.
Rice. 3. The process of formation of lysosomes.
The Golgi complex is most developed in cells that secrete various secrets.
What have we learned?
The Golgi apparatus is an important organelle in plant and animal cells. It consists of membranes that form cavities and are stacked. Proteins, fats, lipids pass through the cavities of the Golgi complex, from which complex compounds are formed that participate in the life of the cell and the organism as a whole. The Golgi apparatus produces "building" material from carbohydrates and lipids, secrets, enzymes, lysosomes.
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The cell is a whole system
A living cell is a unique, perfect, smallest unit of an organism; it is designed in such a way as to use oxygen and nutrients as efficiently as possible, while performing its functions. The organelles vital for the cell are the nucleus, ribosomes, mitochondria, endoplasmic reticulum, Golgi apparatus. Let's talk about the latter in more detail.
What it is
This membrane organelle is a complex of structures that remove the substances synthesized in it from the cell. Most often, it is located near the outer cell membrane.
Golgi apparatus: structure
It consists of "sacs" formed by membranes called cisterns. The latter have an elongated shape, slightly flattened in the middle and expanded along the edges. Also in the complex there are round Golgi vesicles - small membrane structures. Cisterns are “stacked” in stacks called dictyosomes. The Golgi apparatus contains various types of "sacs", the whole complex is divided into some parts according to the degree of remoteness from the nucleus. There are three of them: the cis-section (closer to the nucleus), the median, and the trans-section - the furthest from the nucleus. They are characterized by a different composition of enzymes, and hence the work performed. There is one feature in the structure of dictyosomes: they are polar, that is, the section closest to the nucleus only receives vesicles coming from the endoplasmic reticulum. The part of the "stack" facing the cell membrane only forms and releases them.
Golgi apparatus: functions
The main tasks performed are the sorting of proteins, lipids, mucous secretions and their excretion. Also, non-protein substances secreted by the cell, carbohydrate components of the outer membrane, pass through it. At the same time, the Golgi apparatus is not at all an indifferent intermediary that simply “transfers” substances; processes of activation and modification (“maturation”) take place in it:
- Sorting of substances, transport of proteins. The distribution of protein substances occurs in three streams: for the membrane of the cell itself, export, lysosomal enzymes. In the first stream, in addition to proteins, fats are also included. Interesting fact that any export substances are carried inside the bubbles. But the proteins intended for the cell membrane are integrated into the membrane of the transport vesicle and move in this way.
- Isolation of all products produced in the cell. The Golgi apparatus "packs" all products, both protein and other nature, into secretory vesicles. All substances are released outside through the complex interaction of the latter with the cell membrane.
- Synthesis of polysaccharides (glycosaminoglycans and components of the cell wall glycocalyx).
- Sulfation, glycosylation of fats and proteins, partial proteolysis of the latter (necessary to transfer them from an inactive form to an active one) - these are all the processes of “maturation” of proteins necessary for their future full-fledged work.
Finally
Having considered how the Golgi complex is arranged and works, we are convinced that it is the most important and integral part of any cell (especially secretory ones). A cell that does not produce substances for export also cannot do without this organelle, since the “completeness” of the cell membrane and other important internal life processes depend on it.
Golgi complex.Golgi complex- lamellar complex, it is the most important membrane organelle that controls the processes of intracellular transport.
The main functions of the Golgi apparatus are the modification, accumulation, sorting and direction of various substances into the appropriate intracellular compartments, as well as outside the cell.Structure.
The Golgi complex consists of a set of flattened cisterns surrounded by a membrane, resembling a stack of plates. Each Golgi stack typically contains four to six cisterns, typically about 1 µm in diameter. The number of Golgi stacks in a cell largely depends on its type: some cells contain one large stack, while others have hundreds of very small stacks.
Functions.
1) Transport of substances from the endoplasmic reticulum.
The Golgi apparatus is not symmetrical in structure, the tanks on the side that is closer to the cell nucleus contain the least mature proteins, membrane vesicles continuously attach to these tanks, detaching from the granular endoplasmic reticulum.
2) Modification of proteins in the Golgi apparatus
In the tanks of the Golgi apparatus, proteins intended for excretion, proteins built into the cell membrane, proteins of lysosomes, etc. mature. The maturing proteins sequentially move along the tanks to organelles, in which their modifications occur - glycosylation and phosphorylation.
Glycosylation - attachment of saccharide residues to organic molecules.
Phosphorylation– addition of phosphoric acid residues.In oxygen-glycosylation, complex sugars are attached to proteins through an oxygen atom. During phosphorylation, a residue of phosphoric acid is attached to proteins.
Different tanks of the Golgi apparatus contain different resident catalytic enzymes and, consequently, different processes sequentially occur with maturing proteins in them. It is clear that such a stepwise process must be somehow controlled. Indeed, maturing proteins are “marked” with special polysaccharide residues, apparently playing the role of a kind of “quality mark”.3) Transport of proteins from the Golgi apparatus
Eventually from the extended side of the Golgi Complex (called trance-Golgi) vesicles containing fully mature proteins bud off. The main function of the Golgi apparatus is the sorting of proteins passing through it. In the Golgi apparatus, the formation of a "three-directional protein flow" occurs:
With the help of vesicular transport, the proteins that have passed through the Golgi apparatus are delivered “to the address” depending on the “tags” received by them in the Golgi apparatus.
- maturation and transport of plasma membrane proteins;
- maturation and transport of secretions (secrets);
- maturation and transport of lysosome enzymes.
4) Formation of lysosomes
They bud off from the Golgi apparatus.
5) Transport of proteins to the outer membrane
Modified proteins are detached from the golgi complex into cellular vesicles (vesicles), which deliver them to the cell surface. Such proteins remain in its composition, and are not released into external environment, like those proteins that were in the cavity of the vesicle.
3d model
Location in the cell
Transportation process through the Golgi Complex
Animation view
Foreign video from detailed description transportation process
Organelles- permanent, necessarily present, components of the cell that perform specific functions.
Endoplasmic reticulum
Endoplasmic reticulum (ER), or endoplasmic reticulum (EPR), is a single-membrane organelle. It is a system of membranes that form "tanks" and channels, connected to each other and limiting a single internal space - EPS cavities. On the one hand, the membranes are connected to the cytoplasmic membrane, on the other hand, to the outer nuclear membrane. There are two types of EPS: 1) rough (granular), containing ribosomes on its surface, and 2) smooth (agranular), the membranes of which do not carry ribosomes.
Functions: 1) transport of substances from one part of the cell to another, 2) division of the cytoplasm of the cell into compartments ("compartments"), 3) synthesis of carbohydrates and lipids (smooth ER), 4) protein synthesis (rough ER), 5) place of formation of the Golgi apparatus .
Or golgi complex, is a single-membrane organelle. It is a stack of flattened "tanks" with widened edges. A system of small single-membrane vesicles (Golgi vesicles) is associated with them. Each stack usually consists of 4-6 "tanks", is a structural and functional unit of the Golgi apparatus and is called a dictyosome. The number of dictyosomes in a cell ranges from one to several hundred. In plant cells, dictyosomes are isolated.
The Golgi apparatus is usually located near the cell nucleus (in animal cells often near the cell center).
Functions of the Golgi apparatus: 1) accumulation of proteins, lipids, carbohydrates, 2) modification of incoming organic matter, 3) “packaging” of proteins, lipids, carbohydrates into membrane vesicles, 4) secretion of proteins, lipids, carbohydrates, 5) synthesis of carbohydrates and lipids, 6) site of formation of lysosomes. The secretory function is the most important, therefore the Golgi apparatus is well developed in the secretory cells.
Lysosomes
Lysosomes- single-membrane organelles. They are small bubbles (diameter from 0.2 to 0.8 microns) containing a set of hydrolytic enzymes. Enzymes are synthesized on the rough ER, move to the Golgi apparatus, where they are modified and packaged into membrane vesicles, which, after separation from the Golgi apparatus, become lysosomes proper. A lysosome can contain from 20 to 60 various kinds hydrolytic enzymes. The breakdown of substances by enzymes is called lysis.
Distinguish: 1) primary lysosomes, 2) secondary lysosomes. Primary lysosomes are called lysosomes, detached from the Golgi apparatus. Primary lysosomes are a factor that ensures the exocytosis of enzymes from the cell.
Secondary lysosomes are called lysosomes, formed as a result of the fusion of primary lysosomes with endocytic vacuoles. In this case, they digest substances that have entered the cell by phagocytosis or pinocytosis, so they can be called digestive vacuoles.
Autophagy- the process of destruction of structures unnecessary to the cell. First, the structure to be destroyed is surrounded by a single membrane, then the resulting membrane capsule merges with the primary lysosome, as a result, a secondary lysosome (autophagic vacuole) is also formed, in which this structure is digested. Digestion products are absorbed by the cytoplasm of the cell, but some of the material remains undigested. The secondary lysosome containing this undigested material is called the residual body. By exocytosis, undigested particles are removed from the cell.
Autolysis- self-destruction of the cell, resulting from the release of the contents of lysosomes. Normally, autolysis takes place during metamorphoses (disappearance of the tail of the frog tadpole), involution of the uterus after childbirth, in foci of tissue necrosis.
Functions of lysosomes: 1) intracellular digestion of organic substances, 2) destruction of unnecessary cellular and non-cellular structures, 3) participation in the processes of cell reorganization.
Vacuoles
Vacuoles- single-membrane organelles, are "capacities" filled with aqueous solutions organic and inorganic substances. The ER and the Golgi apparatus take part in the formation of vacuoles. Young plant cells contain many small vacuoles, which then, as the cells grow and differentiate, merge with each other and form one large central vacuole. The central vacuole can occupy up to 95% of the volume of a mature cell, while the nucleus and organelles are pushed back to the cell membrane. The membrane that surrounds the plant vacuole is called the tonoplast. The fluid that fills the plant vacuole is called cell sap. The composition of cell sap includes water-soluble organic and inorganic salts, monosaccharides, disaccharides, amino acids, end or toxic metabolic products (glycosides, alkaloids), some pigments (anthocyanins).
Animal cells contain small digestive and autophagic vacuoles that belong to the group of secondary lysosomes and contain hydrolytic enzymes. Unicellular animals also have contractile vacuoles that perform the function of osmoregulation and excretion.
Vacuole functions: 1) accumulation and storage of water, 2) regulation of water-salt metabolism, 3) maintenance of turgor pressure, 4) accumulation of water-soluble metabolites, reserve nutrients, 5) coloring of flowers and fruits and thereby attracting pollinators and seed dispersers, 6) see. lysosome functions.
Endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles form single vacuolar network of the cell, whose individual elements can transform into each other.
Mitochondria
1 - outer membrane;
2 - inner membrane; 3 - matrix; 4 - crista; 5 - multienzyme system; 6 - circular DNA.
The shape, size, and number of mitochondria are extremely variable. The shape of the mitochondria can be rod-shaped, round, spiral, cup-shaped, branched. The length of mitochondria ranges from 1.5 to 10 µm, the diameter is from 0.25 to 1.00 µm. The number of mitochondria in a cell can reach several thousand and depends on the metabolic activity of the cell.
Mitochondria are bounded by two membranes. The outer membrane of mitochondria (1) is smooth, the inner (2) forms numerous folds - cristae(4). Cristae increase the surface area of the inner membrane, which hosts multienzyme systems (5) involved in the synthesis of ATP molecules. The inner space of mitochondria is filled with matrix (3). The matrix contains circular DNA (6), specific mRNA, prokaryotic-type ribosomes (70S-type), Krebs cycle enzymes.
Mitochondrial DNA is not associated with proteins ("naked"), is attached to the inner membrane of the mitochondria and carries information about the structure of about 30 proteins. Many more proteins are required to build a mitochondrion, so information about most mitochondrial proteins is contained in nuclear DNA, and these proteins are synthesized in the cytoplasm of the cell. Mitochondria are able to reproduce autonomously by dividing in two. Between the outer and inner membranes is proton reservoir, where the accumulation of H + occurs.
Mitochondrial functions: 1) ATP synthesis, 2) oxygen breakdown of organic substances.
According to one of the hypotheses (the theory of symbiogenesis), mitochondria originated from ancient free-living aerobic prokaryotic organisms, which, having accidentally entered the host cell, then formed a mutually beneficial symbiotic complex with it. The following data support this hypothesis. First, mitochondrial DNA has the same structural features as the DNA of modern bacteria (closed in a ring, not associated with proteins). Second, mitochondrial ribosomes and bacterial ribosomes belong to the same type, the 70S type. Thirdly, the mechanism of mitochondrial division is similar to that of bacteria. Fourth, the synthesis of mitochondrial and bacterial proteins is inhibited by the same antibiotics.
plastids
1 - outer membrane; 2 - inner membrane; 3 - stroma; 4 - thylakoid; 5 - grana; 6 - lamellae; 7 - grains of starch; 8 - lipid drops.
Plastids are found only in plant cells. Distinguish three main types of plastids: leukoplasts - colorless plastids in the cells of unstained parts of plants, chromoplasts - colored plastids are usually yellow, red and orange flowers Chloroplasts are green plastids.
Chloroplasts. In the cells of higher plants, chloroplasts have the shape of a biconvex lens. The length of chloroplasts ranges from 5 to 10 microns, the diameter is from 2 to 4 microns. Chloroplasts are bounded by two membranes. The outer membrane (1) is smooth, the inner (2) has a complex folded structure. The smallest fold is called thylakoid(4). A group of thylakoids stacked like a stack of coins is called faceted(5). The chloroplast contains an average of 40-60 grains arranged in a checkerboard pattern. The granules are connected to each other by flattened channels - lamellae(6). The thylakoid membranes contain photosynthetic pigments and enzymes that provide ATP synthesis. The main photosynthetic pigment is chlorophyll, which is responsible for green color chloroplasts.
The inner space of chloroplasts is filled stroma(3). The stroma contains circular naked DNA, 70S-type ribosomes, Calvin cycle enzymes, and starch grains (7). Inside each thylakoid there is a proton reservoir, H + accumulates. Chloroplasts, like mitochondria, are capable of autonomous reproduction by dividing in two. They are contained in the cells of the green parts of higher plants, especially many chloroplasts in leaves and green fruits. The chloroplasts of lower plants are called chromatophores.
Function of chloroplasts: photosynthesis. It is believed that chloroplasts originated from ancient endosymbiotic cyanobacteria (symbiogenesis theory). The basis for this assumption is the similarity of chloroplasts and modern bacteria in a number of ways (circular, "naked" DNA, 70S-type ribosomes, mode of reproduction).
Leukoplasts. The shape varies (spherical, rounded, cupped, etc.). Leucoplasts are bounded by two membranes. The outer membrane is smooth, the inner one forms small thylakoids. The stroma contains circular "naked" DNA, 70S-type ribosomes, enzymes for the synthesis and hydrolysis of reserve nutrients. There are no pigments. Especially many leukoplasts have cells of the underground organs of the plant (roots, tubers, rhizomes, etc.). Function of leukoplasts: synthesis, accumulation and storage of reserve nutrients. Amyloplasts- leukoplasts that synthesize and accumulate starch, elaioplasts- oils, proteinoplasts- squirrels. Different substances can accumulate in the same leukoplast.
Chromoplasts. Limited by two membranes. The outer membrane is smooth, the inner or also smooth, or forms single thylakoids. The stroma contains circular DNA and pigments - carotenoids, which give the chromoplasts a yellow, red or orange color. The form of accumulation of pigments is different: in the form of crystals, dissolved in lipid drops (8), etc. They are contained in the cells of mature fruits, petals, autumn leaves, rarely - root crops. Chromoplasts are considered the final stage of plastid development.
Function of chromoplasts: coloring flowers and fruits and thus attracting pollinators and seed dispersers.
All types of plastids can be formed from proplastids. proplastids- small organelles contained in meristematic tissues. Since plastids have a common origin, interconversions are possible between them. Leukoplasts can turn into chloroplasts (greening of potato tubers in the light), chloroplasts - into chromoplasts (yellowing of leaves and reddening of fruits). The transformation of chromoplasts into leukoplasts or chloroplasts is considered impossible.
Ribosomes
1 - large subunit; 2 - small subunit.
Ribosomes- non-membrane organelles, about 20 nm in diameter. Ribosomes consist of two subunits, large and small, into which they can dissociate. Chemical composition ribosomes are proteins and rRNA. rRNA molecules make up 50-63% of the mass of the ribosome and form its structural framework. There are two types of ribosomes: 1) eukaryotic (with sedimentation constants of the whole ribosome - 80S, small subunit - 40S, large - 60S) and 2) prokaryotic (respectively 70S, 30S, 50S).
Eukaryotic type ribosomes contain 4 rRNA molecules and about 100 protein molecules, while prokaryotic type ribosomes contain 3 rRNA molecules and about 55 protein molecules. During protein biosynthesis, ribosomes can “work” singly or combine into complexes - polyribosomes (polysomes). In such complexes, they are linked to each other by a single mRNA molecule. Prokaryotic cells have only 70S-type ribosomes. Eukaryotic cells have both 80S-type ribosomes (rough ER membranes, cytoplasm) and 70S-type ribosomes (mitochondria, chloroplasts).
Eukaryotic ribosome subunits are formed in the nucleolus. The association of subunits into a whole ribosome occurs in the cytoplasm, as a rule, during protein biosynthesis.
Ribosome function: assembly of the polypeptide chain (protein synthesis).
cytoskeleton
cytoskeleton made up of microtubules and microfilaments. Microtubules are cylindrical unbranched structures. The length of microtubules ranges from 100 µm to 1 mm, the diameter is approximately 24 nm, and the wall thickness is 5 nm. The main chemical component is the protein tubulin. Microtubules are destroyed by colchicine. Microfilaments - threads with a diameter of 5-7 nm, consist of actin protein. Microtubules and microfilaments form complex tangles in the cytoplasm. Functions of the cytoskeleton: 1) determination of the shape of the cell, 2) support for organelles, 3) formation of a division spindle, 4) participation in cell movements, 5) organization of the flow of the cytoplasm.
Includes two centrioles and a centrosphere. Centriole is a cylinder, the wall of which is formed by nine groups of three fused microtubules (9 triplets), interconnected at certain intervals by cross-links. Centrioles are paired, where they are located at right angles to each other. Before cell division, centrioles diverge to opposite poles, and a daughter centriole appears near each of them. They form a spindle of division, which contributes to the uniform distribution of genetic material between daughter cells. In the cells of higher plants (gymnosperms, angiosperms), the cell center does not have centrioles. Centrioles are self-reproducing organelles of the cytoplasm, they arise as a result of duplication of already existing centrioles. Functions: 1) ensuring the divergence of chromosomes to the poles of the cell during mitosis or meiosis, 2) the center of organization of the cytoskeleton.
Organelles of movement
They are not present in all cells. The organelles of movement include cilia (ciliates, epithelium of the respiratory tract), flagella (flagellates, spermatozoa), pseudopods (rhizomes, leukocytes), myofibrils (muscle cells), etc.
Flagella and cilia- organelles of a filamentous form, represent an axoneme bounded by a membrane. Axoneme - cylindrical structure; the wall of the cylinder is formed by nine pairs of microtubules, in its center there are two single microtubules. At the base of the axoneme there are basal bodies represented by two mutually perpendicular centrioles (each basal body consists of nine triplets of microtubules; there are no microtubules in its center). The length of the flagellum reaches 150 µm, the cilia are several times shorter.
myofibrils consist of actin and myosin myofilaments, which provide contraction of muscle cells.
Go to lectures number 6"Eukaryotic cell: cytoplasm, cell wall, structure and functions of cell membranes"
The Golgi apparatus, also known as the Golgi complex, is one of the most important components in the structure of the cell. This cell, named after the Italian biologist Camillo Golgi, who discovered it in 1898, it looks like a complex of cavities bounded by single membranes. In fact, the Golgi apparatus is a membrane structure of a eukaryotic cell.
The structure of the Golgi apparatus
If we look at the Golgi apparatus in electronic, we will see something resembling a stack of sacs superimposed on each other, near which there are many bubbles. In the middle of each such bag is a narrow channel, which expands at the ends into the so-called tanks. From them, in turn, bubbles bud. A system of interconnected tubules is formed around the central stack.
The outer side of the Golgi apparatus has a slightly convex shape, where our stacks form new cisterns by fusion of vesicles budding from the smooth endoplasmic reticulum. WITH inside the apparatus of the tank complete their maturation and also break up again into bubbles. Similarly, there is a movement of tanks (sacs, stacks) from the outer side of the organelle to the inner.
Also, the part of the Golgi complex that is closer to the nucleus of the cell is called "cis", and the part that is closer to the membrane is called "trans".
This is what the Golgi apparatus looks like in the figure.
Functions of the Golgi complex
The role of the Golgi apparatus in the life of the cell is diverse, mainly it comes down to the modification and redistribution of synthesizing substances and also their removal outside the cell, the formation of lysosomes and construction.
The activity of the Golgi apparatus in secretory cells is very high. Proteins that come from the endoplasmic reticulum are concentrated in the Golgi apparatus, then in the Golgi vesicles are transferred to the membrane.
In plant cells, during the formation of the cell wall, it is the Golgi that secretes carbohydrates, which serve as a matrix for it. With the help of microtubules, the budding Golgi vesicles move and their membranes merge with the cytoplasmic membrane, and the contents are included in the cell wall.
The Golgi complex of goblet cells (they are located in the thickness of the epithelium of the intestinal mucosa and respiratory tract) secretes the glycoprotein mucin, it forms mucus.
And in the intestinal cells, it is the Golgi apparatus that performs important function on the movement of lipids. This happens in this way: fatty acids and glycerol enter the cells, then their lipids are synthesized in the endoplasmic reticulum, most of which are covered with proteins and transported to the cell membrane with the help of Golgi, passing through which the lipids will be in the lymph.