The main functions and components of the cytoplasm. The structure and functions of the cytoplasm. Key organelles of the cytoplasm. cytoplasm. Its composition and functions
Along with it, the cytoplasm is one of the main parts of the cell, this building material of any organic matter. The cytoplasm plays a very important role in the life of the cell, it unites all cellular structures, promotes their interaction with each other. Also in the cytoplasm is the nucleus of the cell and that's it. In simple words, the cytoplasm is a substance in which all other components of the cell are located.
The structure of the cytoplasm
The composition of the cytoplasm includes various chemical compounds, which are not a homogeneous chemical substance, but a complex physico-chemical system, it is also constantly changing and developing and has a large water content. An important component of the cytoplasm is a protein mixture in a colloidal state in combination with nucleic acids, fats and carbohydrates.
The cytoplasm is also divided into two parts:
- endoplasm,
- exoplasm.
Endoplasm is located in the center of the cell and has a more fluid structure. It is in it that all the most important organelles of the cell are located. Exoplasm is located along the perimeter of the cell, where it borders on its membrane; it is more viscous and dense in consistency. It plays the role of connecting the cell with the environment.
Cytoplasm drawing.
Functions of the cytoplasm
What is the function of the cytoplasm? Very important - all the processes of cellular metabolism take place in the cytoplasm, with the exception of the synthesis of nucleic acids (it is carried out in the cell nucleus). In addition to this, the most important function, the cytoplasm plays such useful roles:
- fills the cell cavity
- is a link for cellular components,
- determines the position of organelles,
- is a conductor for physical and chemical processes at the intracellular and intercellular levels,
- maintains the internal pressure of the cell, its volume, elasticity, etc.
Movement of the cytoplasm
The ability of the cytoplasm to move is its important property, due to this, the connection of the cell organelles is ensured. In biology, the movement of the cytoplasm is called cyclosis, it is a constant process. The movement of the cytoplasm in the cell can be jet, oscillatory or circular.
Division of the cytoplasm
Another property of the cytoplasm is its division, without which cell division itself would simply be impossible. The division of the cytoplasm is carried out by
2. Structure of the cytoplasm, its chemical composition, significance. The structure and functions of membranes.
Cytoplasm (protoplasm) as the living contents of the cell was already known in the XII century. The term protoplasm was first proposed by the Czech scientist Purkinje (1839).
There are three layers of cytoplasm: plasmalemma, hyaloplasm, tonoplast.
plasmalemma - elementary membrane, the outer layer of the cytoplasm, adjacent to the shell. Its thickness is about 80A (A - angstrom, 10-10 m). Consists of phospholipids, proteins, lipoproteins, carbohydrates, inorganic ions, water. It can have lamellar (layered) and micellar (droplet) structures. Most often it consists of 3 layers: a bimolecular layer of phospholipids (35A), they account for 40%, the surface is covered on both sides with a discontinuous layer of structural proteins (20 and 25A). In some places at the junction of lamellar and micellar structures or between two micelles, the outer and inner layers of structural proteins can merge, forming hydrophilic protein pores, 7-10A, through which substances in the dissolved state pass.
Protein molecules that do not have enzymatic activity are embedded in the membrane matrix - specific selective ionic conduction channels (potassium, sodium, etc.). Finally, the membrane may contain proteins - enzymes that ensure the entry of macromolecular substances into the cell. All these formations - biochemical pores - provide the main property of membranes - semi-permeability.
The plasmalemma has numerous folds, depressions, protrusions, which increases its surface many times over.
As a membrane, the plasmalemma performs important and complex functions: 1. Regulates the intake and release of substances by the cell; 2. Converts, stores and consumes energy; 3. Represents a chemical converter; accelerates the transformation of substances; 4. Receives and converts light, mechanical and chemical signals from the outside world.
Thus, the plasmalemma controls the permeability of the cell, the processes of absorption, transformation, secretion and excretion of substances.
Tonoplast - inner membrane separating the cell sap from the cytoplasm
Hyaloplasm. Represents the basis of cellular organization, is an expression of its essence as a living thing. From a physicochemical point of view, it is a complex heterogeneous colloidal system, where high-molecular compounds are dispersed in an aqueous medium. On average, the cytoplasm contains 70-80% water, 12% proteins, 1.5-2% nucleic acids, about 5% fat, 4-6% carbohydrates and 0.5-2% inorganic substances. It can be in two states: sol and gel. Sol- liquid state, has viscosity, gel- solid state, has elasticity, extensibility. Capable of reversible "sol-gel transition" under the influence of temperature, concentration of hydrogen ions, addition of electrolyte, mechanical impact.
Cytoplasm is in constant movement, which under normal conditions is very slow and almost imperceptible. An increase in temperature, a light or chemical stimulus accelerates the movement of the cytoplasm and makes it visible in a light microscope. Chloroplasts, which are carried away by the current of viscous cytoplasm, help to see this movement. The movement of the cytoplasm is of two types: circular (rotational) and striated (circulating). If the cell cavity is occupied by one large vacuole, then the cytoplasm moves only along the walls. This is a circular motion. It can be observed in the cells of the leaf of Vallisneria, Elodea. If there are several vacuoles in the cell, then the strands of the cytoplasm, crossing the cell, are connected in the center, where the nucleus is located. In these strands there is a striated movement of the cytoplasm. The striated movement of the cytoplasm can be observed in the cells of the stinging hairs of the nettle, in the cells of the hairs of young pumpkin shoots.
The properties of hyaloplasm are also associated with supramolecular structures of a protein nature. These are microtubules and microfilaments.
microtubules- hollow small formations with an electron-dense protein wall. They participate in the conduction of substances through the cytoplasm, in the movement of chromosomes and the formation of mitotic spindle threads.
Microfilaments consist of spirally arranged protein subunits that form fibers or a three-dimensional network, contain contractile proteins and promote the movement of the hyaloplasm and organelles attached to them.
Hyaloplasm as a complex heterogeneous colloidal system of macromolecules and supramolecular structures, it is characterized by insolubility in water, viscosity, elasticity, the ability to reverse changes, obstruction through the pores of natural membranes, large interfaces, strong light refraction, and a very low diffusion rate.
Hyaloplasm organelles . As noted earlier, in the hyaloplasm there are a large number of supramolecular formations, which are numerous organelles.
Functions of biomembranes
1) barrier - provides a regulated, selective, passive and active metabolism with the environment. For example, the peroxisome membrane protects the cytoplasm from peroxides that are dangerous for the cell. Selective permeability means that the permeability of a membrane to various atoms or molecules depends on their size, electrical charge, and chemical properties. Selective permeability ensures the separation of the cell and cellular compartments from the environment and supply them with the necessary substances.
2) transport - through the membrane there is a transport of substances into the cell and out of the cell. Transport through membranes provides: delivery of nutrients, removal of end products of metabolism, secretion of various substances, creation of ionic gradients, maintenance of the appropriate pH and ionic concentration in the cell, which are necessary for the operation of cellular enzymes. Particles that for some reason are not able to cross the phospholipid bilayer (for example, due to hydrophilic properties, since the membrane is hydrophobic inside and does not allow hydrophilic substances to pass through, or because of its large size), but necessary for the cell, they can penetrate the membrane through special carrier proteins (transporters) and channel proteins or by endocytosis. In passive transport, substances cross the lipid bilayer without energy expenditure, by diffusion. A variant of this mechanism is facilitated diffusion, in which a specific molecule helps a substance to pass through the membrane. This molecule may have a channel that allows only one type of substance to pass through. Active transport requires energy, as it occurs against the concentration gradient. There are special pump proteins on the membrane, including ATPase, which actively pumps potassium ions (K+) into the cell and pumps sodium ions (Na+) out of it.
3) matrix - provides a certain relative position and orientation of membrane proteins, their optimal interaction;
4) mechanical - ensures the autonomy of the cell, its intracellular structures, as well as connection with other cells (in tissues). Cell walls play an important role in providing mechanical function, and in animals - intercellular substance.
5) energy - during photosynthesis in chloroplasts and cellular respiration in mitochondria, energy transfer systems operate in their membranes, in which proteins also participate;
6) receptor - some proteins located in the membrane are receptors (molecules with which the cell perceives certain signals). For example, hormones circulating in the blood act only on target cells that have receptors corresponding to these hormones . Neurotransmitters (chemicals that conduct nerve impulses) also bind to specific receptor proteins on target cells.
7) enzymatic - membrane proteins are often enzymes. For example, the plasma membranes of intestinal epithelial cells contain digestive enzymes.
8) the implementation of the generation and conduction of biopotentials.
With the help of the membrane, a constant concentration of ions is maintained in the cell: the concentration of the K + ion inside the cell is much higher than outside, and the concentration of Na + is much lower, which is very important, since this maintains the potential difference across the membrane and generates a nerve impulse.
9) cell marking - there are antigens on the membrane that act as markers - "labels" that allow the cell to be identified. These are glycoproteins (that is, proteins with branched oligosaccharide side chains attached to them) that play the role of "antennas". Due to the myriad of side chain configurations, it is possible to make a specific marker for each cell type. With the help of markers, cells can recognize other cells and act in concert with them, for example, when forming organs and tissues. It also allows the immune system to recognize foreign antigens.
Separated from the environment by the plasmalemma, it includes the main substance (matrix and hyaloplasm), the obligatory cellular components in it - organelles, as well as various non-permanent structures - inclusions.
In an electron microscope, the cytoplasmic matrix looks like a homogeneous or fine-grained substance with a low electron density. The main substance of the cytoplasm fills the space between the plasmalemma, the nuclear membrane and other intracellular structures. Hyaloplasm is a complex colloidal system that includes various biopolymers. The main substance of the cytoplasm forms the true internal environment of the cell, which unites all intracellular structures and ensures their interaction with each other.
In an electron microscope, the cytoplasmic matrix looks like a homogeneous or fine-grained substance with a low electron density. It includes a microtrabecular network formed by thin fibrils 2-3 nm thick and penetrating the entire cytoplasm. The main substance of the cytoplasm should be considered in the same way as a complex colloidal system capable of moving from a liquid state to a gel-like one.
Functions:
It unites all cellular structures and ensures their interaction with each other.
It is a reservoir for enzymes and ATP.
Spare products are put aside.
Various reactions (protein synthesis) take place.
The constancy of the environment.
It is a framework.
Inclusions are called non-permanent components of the cytoplasm, which serve as reserve nutrients, products to be removed from the cell, and ballast substances.
Organelles are permanent structures of the cytoplasm that perform vital functions in the cell.
Non-membrane organelles:
1) Ribosomes- small mushroom-shaped bodies in which protein synthesis takes place. They consist of ribosomal RNA and a protein that forms a large and small subunit.
2) cytoskeleton- the musculoskeletal system of the cell, including non-membrane formations that perform both frame and motor functions in the cell. These filamentous or fibrillar-nye can quickly appear and just as quickly disappear. This system includes fibrillar structures (5-7nm) and microtubules (they consist of 13 subunits).
3) The cell center consists of centrioles (150 nm long, 300-500 nm in diameter) surrounded by centrospheres.
Centrioles are made up of 9 triplets of microtubules. Functions:
The formation of mitotic spindle filaments.
Ensuring the separation of sister chromatids in the anaphase of mitosis.
4) Cilia (A cilia is a thin cylindrical outgrowth of the cytoplasm with a constant diameter of 300 nm. This outgrowth is covered with a plasma membrane from the base to its very top) and flagella (150 microns long) are special movement organelles found in some cells of various organisms .
The cytoplasm is perhaps the most important part of any cell structure, representing a kind of "connective tissue" between all the components of the cell.
The functions and properties of the cytoplasm are diverse; its role in ensuring the life of the cell can hardly be overestimated.
This article describes most of the processes that occur in the smallest living structure at the macro level, where the main role is assigned to the gel-like mass that fills the internal volume of the cell and gives the latter its appearance and shape.
In contact with
The cytoplasm is a viscous (jelly-like) transparent substance that fills every cell and is bounded by the cell membrane. It consists of water, salts, proteins and other organic molecules.
All eukaryotic organelles, such as the nucleus, endoplasmic reticulum, and mitochondria, are located in the cytoplasm. The part of it that is not contained in organelles is called the cytosol. Although it may seem that the cytoplasm has neither shape nor structure, in fact it is a highly organized substance, which is provided by the so-called cytoskeleton (protein structure). The cytoplasm was discovered in 1835 by Robert Brown and other scientists.
Chemical composition
Basically, the cytoplasm is the substance that fills the cell. This substance is viscous, gel-like, 80% water and is usually clear and colorless.
The cytoplasm is the substance of life, which is also called molecular soup, in which cellular organelles are in suspension and connected to each other by a two-layer lipid membrane. The cytoskeleton in the cytoplasm gives it its shape. The process of cytoplasmic flow ensures the movement of useful substances between organelles and the removal of waste products. This substance contains many salts and is a good conductor of electricity.
As stated, substance consists of 70-90% water and is colorless. Most cellular processes take place in it, for example, glycosis, metabolism, cell division processes. The outer transparent glassy layer is called ectoplasm or cell cortex, the inner part of the substance is called endoplasm. In plant cells, the process of cytoplasmic flow takes place, which is the flow of the cytoplasm around the vacuole.
Main characteristics
The following properties of the cytoplasm should be listed:
Structure and components
In prokaryotes (eg bacteria) that do not have a nucleus attached to a membrane, the cytoplasm represents the entire contents of the cell within the plasma membrane. In eukaryotes (for example, plant and animal cells), the cytoplasm is formed by three components that differ from each other: cytosol, organelles, various particles and granules, called cytoplasmic inclusions.
Cytosol, organelles, inclusions
Cytosol is a semi-liquid component located external to the nucleus and inside the plasma membrane. Cytosol makes up approximately 70% of the cell volume and consists of water, cytoskeletal fibers, salts, and organic and inorganic molecules dissolved in water. It also contains proteins and soluble structures such as ribosomes and proteasomes. The inner part of the cytosol, the most fluid and granular, is called the endoplasm.
The network of fibers and high concentrations of dissolved macromolecules, such as proteins, lead to the formation of macromolecular clusters, which greatly affect the transfer of substances between the components of the cytoplasm.
Organoid means "small organ" that is connected to a membrane. Organelles are located inside the cell and perform specific functions necessary to maintain the life of this smallest brick of life. Organelles are small cellular structures that perform specific functions. The following examples can be given:
- mitochondria;
- ribosomes;
- core;
- lysosomes;
- chloroplasts (in plants);
- endoplasmic reticulum;
- golgi apparatus.
Inside the cell is also the cytoskeleton, a network of fibers that help it maintain its shape.
Cytoplasmic inclusions are particles that are temporarily suspended in a jelly-like substance and consist of macromolecules and granules. You can find three types of such inclusions: secretory, nutritional, pigment. Examples of secretory inclusions include proteins, enzymes and acids. Glycogen (glucose storage molecule) and lipids are prime examples of nutritional inclusions, melanin found in skin cells is an example of pigmented inclusions.
Cytoplasmic inclusions, being small particles suspended in the cytosol, represent a diverse range of inclusions present in various types of cells. These can be either calcium oxalate or silicon dioxide crystals in plants, or starch and glycogen granules. A wide range of inclusions are lipids having a spherical shape, present in both prokaryotes and eukaryotes, and serving for the accumulation of fats and fatty acids. For example, such inclusions occupy most of the volume of adiposites - specialized storage cells.
Functions of the cytoplasm in the cell
The most important functions can be represented in the form of the following table:
- providing the shape of the cell;
- habitat for organoids;
- transport of substances;
- supply of nutrients.
The cytoplasm serves to support organelles and cellular molecules. Many cellular processes take place in the cytoplasm. Some of these processes include protein synthesis, the first step in cellular respiration, which bears the name glycolysis, mitosis and meiosis processes. In addition, the cytoplasm helps hormones move around the cell, and waste products are also removed through it.
Most of the different actions and events take place in this gelatinous liquid, which contains enzymes that contribute to the decomposition of waste products, and many metabolic processes also take place here. The cytoplasm provides the cell with a form, filling it, helps to maintain the organelles in their places. Without it, the cell would look "deflated", and various substances could not easily move from one organelle to another.
Transport of substances
The liquid substance of the contents of the cell is very important for maintaining its vital activity, since allows easy exchange of nutrients between organelles. Such an exchange is due to the process of cytoplasmic flow, which is the flow of the cytosol (the most mobile and fluid part of the cytoplasm), carrying nutrients, genetic information and other substances from one organoid to another.
Some of the processes that take place in the cytosol include also metabolite transfer. The organoid can produce amino acids, fatty acids, and other substances that travel through the cytosol to the organoid that needs these substances.
Cytoplasmic currents lead to the fact that the cell itself can move. Some of the smallest life structures are equipped with cilia (small, hair-like structures on the outside of the cell that allow the latter to move through space). For other cells, for example, amoeba, the only way to move is the movement of fluid in the cytosol.
Supply of nutrients
In addition to the transport of various material, the liquid space between organelles acts as a kind of storage chamber for these materials until the moment when they are really needed by one or another organoid. Within the cytosol, proteins, oxygen, and various building blocks are suspended. In addition to useful substances, the cytoplasm also contains metabolic products that are waiting for their turn until the removal process removes them from the cell.
plasma membrane
The cell, or plasma, membrane is a formation that prevents the cytoplasm from flowing out of the cell. This membrane is composed of phospholepids forming a lipid bilayer that is semi-permeable: only certain molecules can pass through this layer. Proteins, lipids, and other molecules can cross the cell membrane through the process of endocytosis, which forms a vesicle of these substances.
The bubble, which includes liquid and molecules, detaches from the membrane, forming an endosome. The latter moves inside the cell to its recipients. Waste products are excreted through the process of exocytosis. In this process, the vesicles formed in the Golgi apparatus are connected to the membrane, which pushes their contents into the environment. The membrane also provides the shape of the cell and serves as a support platform for the cytoskeleton and cell wall (in plants).
Plant and animal cells
The similarity of the internal contents of plant and animal cells speaks of their identical origin. The cytoplasm provides mechanical support to the internal structures of the cell, which are suspended in it.
The cytoplasm maintains the shape and consistency of the cell and contains many chemicals that are key to maintaining life processes and metabolism.
Metabolic reactions such as glycosis and protein synthesis take place in the jelly-like contents. In plant cells, unlike animals, there is a movement of the cytoplasm around the vacuole, which is known as cytoplasmic flow.
The cytoplasm of animal cells is a substance similar to a gel dissolved in water, it fills the entire volume of the cell and contains proteins and other important molecules necessary for life. The gel-like mass contains proteins, hydrocarbons, salts, sugars, amino acids and nucleotides, all cellular organelles and the cytoskeleton.
The gel-like contents of the cell, bounded by a membrane, is called the cytoplasm of a living cell. The concept was introduced in 1882 by the German botanist Eduard Strasburger.
Structure
The cytoplasm is the internal environment of any cell and is characteristic of bacterial, plant, fungal, and animal cells.
The cytoplasm consists of the following components:
- hyaloplasms (cytosols) - liquid substance;
- cellular inclusions - optional components of the cell;
- organoids - permanent components of the cell;
- cytoskeleton - cell scaffold.
The chemical composition of the cytosol includes the following substances:
- water - 85%;
- proteins - 10%
- organic compounds - 5%.
Organic compounds include:
- mineral salts;
- carbohydrates;
- lipids;
- nitrogen-containing compounds;
- a small amount of DNA and RNA;
- glycogen (characteristic of animal cells).
Rice. 1. The composition of the cytoplasm.
The cytoplasm contains a supply of nutrients (drops of fat, grains of polysaccharides), as well as insoluble waste products of the cell.
The cytoplasm is colorless and constantly moving, flowing. It contains all the organelles of the cell and carries out their relationship. With partial removal, the cytoplasm is restored. When the cytoplasm is completely removed, the cell dies.
The structure of the cytoplasm is heterogeneous. Conditionally allocate two layers of cytoplasm:
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- ectoplasm (plasmagel) - an outer dense layer that does not contain organelles;
- endoplasm (plasmasol) - the inner more liquid layer containing organelles.
The division into ectoplasm and endoplasm is pronounced in protozoa. Ectoplasm helps the cell move.
Outside, the cytoplasm is surrounded by a cytoplasmic membrane or plasmalemma. It protects the cell from damage, selectively transports substances and provides cell irritability. The membrane is made up of lipids and proteins.
vitality
Cytoplasm is a vital substance involved in the main processes of the cell:
- metabolism;
- growth;
- division.
The movement of the cytoplasm is called cyclosis or cytoplasmic flow. It is carried out in eukaryotic cells, including humans. During cyclosis, the cytoplasm delivers substances to all cell organelles, carrying out cellular metabolism. The cytoplasm moves through the cytoskeleton with the consumption of ATP.
With an increase in the volume of the cytoplasm, the cell grows. The process of dividing the body of a eukaryotic cell after nuclear division (karyokinesis) is called cytokinesis. As a result of division of the body, the cytoplasm, together with organelles, is distributed between two daughter cells.
Rice. 2. Cytokinesis.
Functions
The main functions of the cytoplasm in the cell are described in the table.
The separation of the cytoplasm from the membrane by osmosis of water escaping to the outside is called plasmolysis. The reverse process - deplasmolysis - occurs when a sufficient amount of water enters the cell. Processes are characteristic of any cell, except for the animal.