Plants and fungi are composed of three main parts: the plasma membrane, the nucleus and the cytoplasm. Bacteria differ from them in that they do not have a nucleus, but they also have a membrane and cytoplasm.
How is the cytoplasm structured?
This is the inner part of the cell, in which hyaloplasm (liquid medium), inclusions and inclusions can be distinguished. Inclusions are non-permanent formations in the cell, which are mainly drops or crystals of spare nutrients. Organelles are permanent structures. Just as in the body the main functional units are organs, so in a cell all the main functions are performed by organelles.
Membrane and non-membrane cell organelles
The former are divided into single-membrane and double-membrane. The last two are mitochondria and chloroplasts. Single-membrane cells include lysosomes, Golgi complex, reticulum), and vacuoles. We will talk more about non-membrane organelles in this article.
Cell organelles of non-membrane structure
These include ribosomes, the cell center, as well as the cytoskeleton formed by microtubules and microfilaments. Also included in this group are the organelles of movement possessed by unicellular organisms, as well as male reproductive cells of animals. Let's look in order at the non-membrane cell organelles, their structure and functions.
What are ribosomes?
These are cells that consist of ribonucleoproteins. Their structure includes two parts (subunits). One of them is small, one is large. IN calm state they are located separately. They connect when the ribosome begins to function.
These non-membrane cell organelles are responsible for protein synthesis. Namely, for the process of translation - the connection of amino acids into a polypeptide chain in a certain order, information about which is copied from DNA and recorded on mRNA.
The size of ribosomes is twenty nanometers. The number of these organelles in a cell can reach up to several tens of thousands.
In eukaryotes, ribosomes are found both in the hyaloplasm and on the surface of the rough endoplasmic reticulum. They are also present inside double-membrane organelles: mitochondria and chloroplasts.
Cell center
This organelle consists of a centrosome, which is surrounded by a centrosphere. The centrosome is represented by two centrioles - empty inside cylinders consisting of microtubules. The centrosphere consists of microtubules extending radially from the cell center. It also contains intermediate filaments and microfibrils.
The cell center performs functions such as the formation of a division spindle. It is also the center of microtubule organization.
Concerning chemical structure of this organelle, the main substance is the protein tubulin.
This organelle is located in the geometric center of the cell, which is why it has this name.
Microfilaments and microtubules
The first are filaments of the protein actin. Their diameter is 6 nanometers.
The diameter of microtubules is 24 nanometers. Their walls are made of the protein tubulin.
These nonmembrane cell organelles form a cytoskeleton that helps maintain a constant shape.
Another function of microtubules is transport; organelles and substances in the cell can move along them.
Locomotion organoids
They come in two types: cilia and flagella.
The first are unicellular organisms such as slipper ciliates.
Chlamydomonas have flagella, as well as animal sperm.
Locomotion organelles consist of contractile proteins.
Conclusion
As a conclusion, we provide generalized information.
| Organoid | Location in the cage | Structure | Functions |
| Ribosomes | They float freely in the hyaloplasm and are also located on the outer side of the walls of the rough endoplasmic reticulum | Consist of small and large parts. Chemical composition - ribonucleoproteins. | Protein synthesis |
| Cell center | Geometric center of the cell | Two centrioles (cylinders of microtubules) and a centrosphere - radially extending microtubules. | Spindle formation, microtubule organization |
| Microfilaments | In the cytoplasm of the cell | Thin filaments made from the contractile protein actin | Creating support, sometimes providing movement (for example, in amoebas) |
| Microtubules | In the cytoplasm | Hollow tubulin tubes | Creation of support, transport of cell elements |
| Cilia and flagella | From the outside of the plasma membrane | Made up of proteins | Movement of a single-celled organism in space |
So we looked at all the non-membrane organelles of plants, animals, fungi and bacteria, their structure and functions.
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 organelles cells
1. Endoplasmic reticulum(EPS) - a system of internal membranes of the cytoplasm, forming large cavities - cisterns and numerous tubules; takes 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. On the membranes of the Golgi apparatus, enzyme systems involved in the formation of more complex organic compounds from proteins, fats and carbohydrates synthesized in EPS. 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 cell center The 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 structure plan - the outer part of the flagellum faces environment and is covered by a portion 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, ensures movement cellular structures through the cytoplasm.
2.3. Let us take a closer look at the work of the carrier protein, which ensures passive transport of substances across the cell membrane. The process by which carrier proteins bind and transport dissolved molecules resembles an enzymatic reaction. All types of carrier proteins contain binding sites for the transported molecule. When the protein is saturated, the transport rate is maximum. Binding can be blocked either by competitive inhibitors (competing for the same binding site) or by non-competitive inhibitors that bind elsewhere and affect the structure of the transporter. The molecular mechanism of transporter proteins is not yet known. It is assumed that they transport molecules by undergoing reversible conformational changes that allow their binding sites to be located alternately on one side or the other of the membrane. This diagram presents a model showing how conformational changes in a protein could allow facilitated diffusion of a solute. The transporter protein can exist in two conformational states: “ping” and “pong”. The transition between them is random and completely reversible. However, the probability of a molecule of the transported substance binding to a protein is much higher in the “ping” state. Therefore, there will be much more molecules moved into the cell than those that leave it. The substance is transported along an electrochemical gradient.
Some transport proteins simply transfer some solute from one side of the membrane to the other. This transfer is called uniport. Other proteins are contransport systems. They establish the following principles:
a) the transfer of one substance depends on the simultaneous (sequential) transfer of another substance in the same direction (symport).
b) the transfer of one substance depends on the simultaneous (sequential) transfer of another substance in the opposite direction (antiport).
For example, most animal cells absorb glucose from the extracellular fluid, where its concentration is high, through passive transport carried out by a protein that acts as a uniporter. At the same time, intestinal and kidney cells absorb it from the lumenal space of the intestine and from the renal tubules, where its concentration is very low, through the symport of glucose and Na ions.
A type of facilitated diffusion is transport using immobile carrier molecules fixed in a certain way across the membrane. In this case, a molecule of the transported substance is transferred from one carrier molecule to another, as if in a relay race.
An example of a carrier protein is valinomycin, a potassium ion transporter. The valinomycin molecule has the shape of a cuff, lined with polar groups on the inside and non-polar on the outside.
Due to the peculiarity of its chemical structure, valinomycin is capable of forming a complex with potassium ions that enter the inside of the molecule - the cuff, and on the other hand, valinomycin is soluble in the lipid phase of the membrane, since the outside of its molecule is non-polar. Valinomycin molecules located at the surface of the membrane can capture potassium ions from the surrounding solution. As molecules diffuse through the membrane, they carry potassium across the membrane, and some of them release ions into the solution on the other side of the membrane. This is how valinomycin transfers potassium ions across the membrane.
Differences between facilitated diffusion and simple diffusion:
1) transfer of a substance with the participation of a carrier occurs much faster;
2) facilitated diffusion has the property of saturation: with increasing concentration on one side of the membrane, the flux density of the substance increases only to a certain limit, when all the carrier molecules are already occupied;
3) with facilitated diffusion, competition between transported substances is observed in cases where the carrier transports different substances; Moreover, some substances are better tolerated than others, and the addition of some substances complicates the transport of others; Thus, among sugars, glucose is better tolerated than fructose, fructose is better than xylose, and xylose is better than arabinose, etc. etc.;
4) there are substances that block facilitated diffusion - they form a strong complex with carrier molecules, for example, phloridzin inhibits the transport of sugars through a biological membrane.
2.4. Filtration is the movement of a solution through pores in a membrane under the influence of a pressure gradient. She plays important role in the processes of water transfer through the walls of blood vessels.
So, we have examined the main types of passive transport of molecules through biological membranes.
2.5. It is often necessary to ensure the transport of molecules across a membrane against their electrochemical gradient. This process is called active transport and is carried out by carrier proteins, whose activity requires energy. If you connect a carrier protein with an energy source, you can get a mechanism that ensures the active transport of substances across the membrane. One of the main sources of energy in the cell is the hydrolysis of ATP to ADP and phosphate. The mechanism (Na + K) pump, which is important for the life of the cell, is based on this phenomenon. He serves wonderful
an example of active ion transport. The concentration of K inside the cell is 10-20 times higher than outside. For Na the picture is opposite. This difference in concentrations is ensured by the operation of the (Na + K) pump, which actively pumps Na out of the cell and K into the cell. It is known that the operation of the (Na + K) pump consumes almost a third of the total energy necessary for the life of the cell. The above concentration difference is maintained for the following purposes:
1) Regulation of cell volume due to osmotic effects.
2) Secondary transport of substances (will be discussed below).
It was experimentally found that:
a) The transport of Na and K ions is closely related to the hydrolysis of ATP and cannot occur without it.
b) Na and ATP must be inside the cell, and K outside.
c) The substance ouabain inhibits ATPase only when outside the cell, where it competes for the binding site with K. (Na + K)-ATPase actively transports Na outside and K inside the cell. When one ATP molecule is hydrolyzed, three Na ions are pumped out of the cell and two K ions enter it.
1) Na binds to protein.
2) Phosphorylation of ATPase induces conformational changes in the protein, resulting in:
3) Na is transferred to the outside of the membrane and released.
4) K binding on the outer surface.
5) Dephosphorylation.
6) Release of K and return of the protein to its original state.
In all likelihood, the (Na + K) pump has three Na binding sites and two K binding sites. The (Na + K) pump can be made to work in the opposite direction and synthesize ATP. If the concentrations of ions on the corresponding sides of the membrane are increased, they will pass through it according to their electrochemical gradients, and ATP will be synthesized from orthophosphate and ADP by (Na + K)-ATPase.
2.6. If the cell did not have systems for regulating osmotic pressure, then the concentration of solutes inside it would be greater than their external concentrations. Then the concentration of water in the cell would be less than its concentration outside. As a result, there would be a constant flow of water into the cell and its rupture. Fortunately, animal cells and bacteria control the osmotic pressure in their cells by actively pumping out inorganic ions such as Na. Therefore, their total concentration inside the cell is lower than outside. Plant cells have rigid walls that protect them from swelling. Many protozoa avoid bursting from the water entering the cell with the help of special mechanisms that regularly throw out the incoming water.
2.7. Another important type of active transport is active transport using ion gradients. This type of penetration through the membrane is carried out by some transport proteins that work on the principle of symport or antiport with some ions, the electrochemical gradient of which is quite high. In animal cells, the transported ion is usually Na. Its electrochemical gradient provides energy for the active transport of other molecules. For example, consider the operation of a pump that pumps glucose. The pump randomly oscillates between ping and pong states. Na binds to the protein in both its states and at the same time increases the latter's affinity for glucose. Outside the cell, the addition of Na, and therefore glucose, occurs more often than inside. Therefore, glucose is pumped into the cell. So, along with the passive transport of Na ions, glucose symport occurs. Strictly speaking, the necessary energy for the operation of this mechanism is accumulated during operation
(Na + K) pump in the form of the electrochemical potential of Na ions. In bacteria and plants, most active transport systems of this type use the H ion as the transported ion. For example, the transport of most sugars and amino acids into bacterial cells is determined by the H gradient.
Organoids- permanent, necessarily present, components of the cell that perform specific functions.
Endoplasmic reticulum (ER)- single-membrane organelle. It is a system of membranes that form “cisterns” and channels, connected to each other and delimiting a single internal space - the EPS cavities. The membranes are connected on one side to the cytoplasm. plasma membrane, on the other hand, with 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 cell cytoplasm into (“compartments”,
3) synthesis of carbohydrates and lipids (smooth EPS),
4) protein synthesis (rough EPS),
Golgi apparatus, is a single-membrane organelle. It consists of stacks of flattened “cisterns” with widened edges. Associated with them is a system of small single-membrane vesicles.
Functions of the Golgi apparatus: 1) accumulation of proteins, lipids, carbohydrates, 2) “packaging” of proteins, lipids, carbohydrates into membrane vesicles, 4) synthesis of carbohydrates and lipids, 6) place of formation of 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 and move to the Golgi apparatus, where they are modified and packaged into membrane vesicles, which, after separation from the Golgi apparatus, become lysosomes themselves. A lysosome can contain from 20 to 60 various types hydrolytic enzymes
Functions of lysosomes: 1) intracellular digestion organic matter, 2) destruction of unnecessary cellular and non-cellular structures,
3) participation in the processes of cell reorganization.
Vacuoles- single-membrane organelles are “containers” filled aqueous solutions organic and inorganic substances.. 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 mature cell, the nucleus and organelles are pushed towards the cell membrane.. The liquid that fills the plant vacuole is called cell sap.
Unicellular animals also have contractile vacuoles that perform the function of osmoregulation and excretion.
Functions of the vacuole: 1) accumulation and water storage,
2) regulation water-salt metabolism,
3) maintaining turgor pressure,
4) accumulation of water-soluble metabolites, reserve nutrients,
5) see functions of lysosomes.
Mitochondria
Mitochondria structure:
1 - outer membrane;
2 - internal membrane; 3 - matrix; 4 - crista; 5 - multienzyme system; 6 - circular DNA.
The shape, size and number of mitochondria vary enormously. Mitochondria can be rod-shaped, round, spiral, cup-shaped, or branched in shape. The length of mitochondria ranges from 1.5 to 10 µm, diameter - 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.
The mitochondrion is bounded by two membranes. The outer membrane of mitochondria is smooth, the inner one forms numerous folds - cristas..Cristae increase the surface area of the inner membrane, on which multienzyme systems (5) involved in the synthesis of ATP molecules are located. The internal space of mitochondria is filled with matrix (3). The matrix contains circular DNA (6), specific mRNA, and ribosomes.
Functions of mitochondria: 1) ATP synthesis, 2) oxygen breakdown of organic substances.
Plastids
Plastid structure: 1 - outer membrane; 2 - internal membrane; 3 - stroma; 4 - thylakoid; 5 - grain; 6 - lamellae; 7 - starch grains; 8 - lipid drops.
Plastids are characteristic only of plant cells. Distinguish three main types of plastids:
leucoplasts - colorless plastids in the cells of uncolored parts of plants,
chromoplasts - colored plastids usually yellow, red and orange,
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 µm, diameter - from 2 to 4 µm. Chloroplasts are bounded by two membranes. The outer membrane is smooth, the inner one has a complex folded structure. The smallest fold is called thylakoid.. A group of thylakoids arranged like a stack of coins is called facet .
The interior space of the chloroplasts is filled stroma. The stroma contains circular “naked” DNA, ribosomes
Function of chloroplasts: photosynthesis.
Leukoplasts. The shape varies (spherical, round, cupped, etc.). Leukoplasts are bounded by two membranes. The outer membrane is smooth, the inner one forms few thylakoids. The stroma contains circular “naked” DNA and ribosomes. There are no pigments. The cells of the underground organs of the plant (roots, tubers, rhizomes, etc.) have especially many leukoplasts.
Function of leucoplasts: synthesis, accumulation and storage of reserve nutrients.
Chromoplasts. Bounded by two membranes. The outer membrane is smooth, the inner membrane is either smooth or forms single thylakoids. The stroma contains circular DNA and pigments that give chromoplasts a yellow, red or orange color. Chromoplasts are considered the final stage of plastid development.
Function of chromoplasts: coloring flowers and fruits and thereby attracting pollinators and seed dispersers.
Structure and functions of the nucleus
Typically, a eukaryotic cell has one core, but there are binucleate (ciliates) and multinucleate 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, ellipsoidal, bean-shaped, etc. The diameter of the nucleus is usually from 3 to 10 microns.
Core structure:
1 - outer membrane; 2 - internal membrane; 3 - pores; 4 - nucleolus; 5 - heterochromatin; 6 - euchromatin.
The nucleus is delimited from the cytoplasm by two membranes (each of them has 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 through which the exchange of substances occurs between the nucleus and the cytoplasm. The outer nuclear membrane on the side facing the cytoplasm is covered with ribosomes, giving it roughness; the inner membrane is smooth.
Kernel functions: 1) storage of hereditary information and transmission of it to daughter cells during division, 2) regulation of cell activity by regulating the synthesis of various proteins, 3) place of formation of ribosomal subunits
Related information.
Organelles (from the Greek organon - tool, organ and idos - type, likeness) are supramolecular structures of the cytoplasm that perform specific functions, without which normal cell activity is impossible. Based on their structure, organelles are divided into non-membrane (not containing membrane components) and membrane (having membranes). Membrane organelles (endoplasmic reticulum, Golgi complex, lysosomes, peroxisomes, mitochondria and plastids) are characteristic only of eukaryotic cells. Non-membrane organelles include the cell center of eukaryotic cells and ribosomes, which are present in the cytoplasm of both eukaryotic and prokaryotic cells. Thus, the only organelle that is universal for all cell types is ribosomes.
Membrane organelles
The main component of membrane organelles is the membrane. Biological membranes are built according to general principle, But chemical composition membranes of different organelles are different. All cell membranes- these are thin films (7–10 nm thick), the basis of which is a double layer of lipids (bilayer), arranged so that the charged hydrophilic parts of the molecules are in contact with the medium, and the hydrophobic residues fatty acids of each monolayer are directed into the membrane and are in contact with each other. Protein molecules (integral membrane proteins) are built into the lipid bilayer in such a way that the hydrophobic parts of the protein molecule are in contact with the fatty acid residues of the lipid molecules, and the hydrophilic parts are exposed to the environment. In addition, part of the soluble (non-membrane proteins) connects to the membrane mainly due to ionic interactions (peripheral membrane proteins). Carbohydrate fragments are also attached to many proteins and lipids in membranes. Thus, biological membranes are lipid films into which integral proteins are embedded.
One of the main functions of membranes is to create a boundary between the cell and the environment and the various compartments of the cell. The lipid bilayer is permeable mainly to fat-soluble compounds and gases; hydrophilic substances are transported across membranes using special mechanisms: low molecular weight substances using various carriers (channels, pumps, etc.), and high molecular weight substances using the processes of exo- and endocytosis.
During endocytosis, certain substances are sorbed on the surface of the membrane (due to interaction with membrane proteins). At this point, an invagination of the membrane into the cytoplasm is formed. A vial containing the transferred compound is then separated from the membrane. Thus, endocytosis is the transfer of high-molecular compounds into the cell external environment, surrounded by a section of membrane. The reverse process, that is, exocytosis, is the transfer of substances from the cell to the outside. It occurs by fusion with the plasma membrane of a vesicle filled with transported high-molecular compounds. The membrane of the vesicle merges with the plasma membrane, and its contents pour out.
Channels, pumps, and other transporters are molecules of integral membrane proteins that typically form a pore in the membrane.
In addition to the functions of separating space and ensuring selective permeability, membranes are capable of sensing signals. This function is performed by receptor proteins that bind signaling molecules. Individual membrane proteins are enzymes that carry out specific chemical reactions.
Single-membrane organelles
1. Endoplasmic reticulum (ER)
EPS is a single-membrane organelle consisting of cavities and tubules connected to each other. The endoplasmic reticulum is structurally connected to the nucleus: a membrane extends from the outer membrane of the nucleus, forming the walls of the endoplasmic reticulum. There are 2 types of EPS: rough (granular) and smooth (agranular). Both types of EPS are present in any cell.
On the membranes of the rough ER there are numerous small granules - ribosomes, special organelles with the help of which proteins are synthesized. Therefore, it is not difficult to guess that proteins are synthesized on the surface of the rough EPS, which penetrate inside the rough EPS and can move through its cavities to any place in the cell.
The membranes of smooth ER are devoid of ribosomes, but enzymes that carry out the synthesis of carbohydrates and lipids are built into its membranes. After synthesis, carbohydrates and lipids can also move along the EPS membranes to any place in the cell. The degree of development of the EPS type depends on the specialization of the cell. For example, in cells that synthesize protein hormones, granular EPS will be better developed, and in cells that synthesize fat-like substances, agranular EPS will be better developed.
EPS functions:
1. Synthesis of substances. Proteins are synthesized on the rough ER, and lipids and carbohydrates are synthesized on the smooth ER.
2. Transport function. Through the cavities of the ER, synthesized substances move to any place in the cell.
2. Golgi complex
The Golgi complex (dictyosome) is a stack of flat membrane sacs called cisternae. The tanks are completely isolated from each other and are not connected to each other. Along the edges of the tanks numerous tubes and bubbles branch off. From time to time, vacuoles (vesicles) with synthesized substances are detached from the EPS, which move to the Golgi complex and connect with it. Substances synthesized in the ER become more complex and accumulate in the Golgi complex.
Functions of the Golgi complex
1. In the tanks of the Golgi complex, further chemical transformation and complication of substances entering it from the EPS occurs. For example, substances necessary to renew the cell membrane (glycoproteins, glycolipids) and polysaccharides are formed.
2. In the Golgi complex, substances accumulate and are temporarily “stored”
3. The formed substances are “packed” into vesicles (vacuoles) and in this form move throughout the cell.
4. Lysosomes (spherical organelles with digestive enzymes) are formed in the Golgi complex.
3. Lysosomes (“lysis” - disintegration, dissolution)
Lysosomes are small spherical organelles, the walls of which are formed by a single membrane; contain lytic (breaking down) enzymes. First, lysosomes detached from the Golgi complex contain inactive enzymes. Under certain conditions, their enzymes are activated. When a lysosome merges with a phagocytotic or pinocytotic vacuole, a digestive vacuole is formed, in which intracellular digestion of various substances occurs.
Functions of lysosomes:
1. They break down substances absorbed as a result of phagocytosis and pinocytosis. Biopolymers are broken down into monomers, which enter the cell and are used for its needs. For example, they can be used to synthesize new organic substances or can be further broken down to produce energy.
2. Destroy old, damaged, redundant organelles. The breakdown of organelles can also occur during cell starvation.
3. Carry out autolysis (cleavage) of the cell (resorption of the tail in tadpoles, liquefaction of tissues in the area of inflammation, destruction of cartilage cells in the process of formation bone tissue and etc.).
4. Vacuoles
Vacuoles are spherical single-membrane organelles that are reservoirs of water and substances dissolved in it. Vacuoles include: phagocytotic and pinocytotic vacuoles, digestive vacuoles, vesicles detached from the ER and the Golgi complex. Vacuoles animal cell- small, numerous, but their volume does not exceed 5% of the total volume of the cell. Their main function is the transport of substances throughout the cell and the interaction between organelles.
In a plant cell, vacuoles account for up to 90% of the volume. In mature plant cell there is only one vacuole, occupying a central position. The membrane of the plant cell vacuole is the tonoplast, its contents are cell sap. Functions of vacuoles in a plant cell: maintaining the cell membrane in tension, accumulating various substances, including cell waste. Vacuoles supply water for photosynthesis processes.
Cell sap may contain:
Reserve substances that can be used by the cell itself (organic acids, amino acids, sugars, proteins).
- substances that are removed from the cell’s metabolism and accumulate in the vacuole (phenols, tannins, alkaloids, etc.)
- phytohormones, phytoncides,
- pigments (coloring substances) that give cell sap a purple, red, blue, violet, and sometimes yellow or cream color. It is the pigments of cell sap that color flower petals, fruits, and roots.
Tubular-vacuolar system of the cell (system of transport and synthesis of substances)
The ER, Golgi complex, lysosomes and vacuoles form a single tubular-vacuolar system of the cell. All its elements have a similar chemical composition of membranes, so their interaction is possible. All elements of the FAC originate from the EPS. Vacuoles that enter the Golgi complex are detached from the EPS; vesicles that merge with the cell membrane, lysosomes, are detached from the Golgi complex.
FAC value:
1. KBC membranes divide the contents of the cell into separate compartments (compartments) in which certain processes take place. This makes it possible for various processes, sometimes directly opposite, to occur simultaneously in the cell.
2. As a result of the activity of the CVS, the cell membrane is constantly renewed.
Double membrane organelles
A double-membrane organelle is a hollow structure whose walls are formed by a double membrane. There are 2 types of double-membrane organelles: mitochondria and plastids. Mitochondria are characteristic of all eukaryotic cells; plastids are found only in plant cells. Mitochondria and plastids are components of the cell’s energy system; as a result of their functioning, ATP is synthesized.
The mitochondrion is a two-membrane semi-autonomous organelle that synthesizes ATP.
The shape of mitochondria is varied; they can be rod-shaped, filamentous or spherical. The walls of mitochondria are formed by two membranes: outer and inner. The outer membrane is smooth, and the inner one forms numerous folds - cristae. The inner membrane contains numerous enzyme complexes that carry out the synthesis of ATP.
Plant cells have special double-membrane organelles - plastids. There are 3 types of plastids: chloroplasts, chromoplasts, leucoplasts.
Chloroplasts have a shell of 2 membranes. Outer shell smooth, and the inner one forms numerous vesicles (thylakoids). A stack of thylakoids is a grana. Granules are staggered for better penetration sunlight. The thylakoid membranes contain molecules of the green pigment chlorophyll, so chloroplasts have green color. Photosynthesis occurs with the help of chlorophyll. Thus, main function chloroplasts - carrying out the process of photosynthesis.
Chromoplasts are plastids that are red, orange or yellow in color. Chromoplasts are colored by carotenoid pigments located in the matrix. Thylakoids are poorly developed or absent altogether. The exact function of chromoplasts is unknown. Perhaps they attract animals to the ripe fruits.
Leukoplasts are colorless plastids located in the cells of colorless tissues. Thylakoids are undeveloped. Leukoplasts accumulate starch, lipids and proteins.
Plastids can mutually transform into each other: leucoplasts - chloroplasts - chromoplasts.
