What is cytoplasm and what are its functions? Nutrient supply
Cytoplasm- this is the internal environment of the cell, limited by the cell membrane, except for the nucleus and vacuole. It was previously said that the cell consists of 80% water. A feature of the structure of the cell cytoplasm is that most of the cell’s water structure is in the cytoplasm. The solid part of the cytoplasm includes proteins, carbohydrates, phospholipids, cholesterol and other nitrogen-containing organic compounds, mineral salts, inclusions in the form of glycogen droplets (in animal cells) and other substances. Almost all processes of cellular metabolism take place in the cytoplasm. The cytoplasm also contains reserve nutrients and insoluble waste products from metabolic processes.
Functions of the cytoplasm or the role of the cytoplasm in the cell
Functions of the cytoplasm or role of the cytoplasm:
1. Connect all parts of the cell into a single whole;
2. Chemical processes take place in it;
3. Transports substances;
4. Performs a support function.
TO structural features of the cytoplasm the following can be attributed:
1. Colorless viscous substance;
2. Is in constant motion;
3. Contains organelles (permanent structural components and cellular inclusions, and non-permanent structural cells);
4. Inclusions can be in the form of drops (fats) and grains (proteins and carbohydrates).
You can see what the cytoplasm looks like using the example of the structure of a plant cell or animal cell.
Movement of the cytoplasm
The movement of cytoplasm in the cell is virtually continuous. The movement of the cytoplasm itself is carried out due to the cytoskeleton, or more precisely due to changes in the shape of the cytoskeleton.
Cytoplasmic organoids
Organoids of the cell cytoplasm include all organoids located in the cell, since they are all located inside the cytoplasm. All organelles in the cytoplasm are in a mobile state and can move due to the cytoskeleton.
Composition of the cytoplasm
The composition of the cytoplasm includes:
1. Water approximately 80%;
2. Protein about 10%;
3. Lipids about 2%;
4. Organic salts about 1%;
5. Inorganic salts 1%;
6. RNA approximately 0.7%;
7. DNA approximately 0.4%.
The above composition of the cytoplasm is true for eukaryotic cells.
1. Give examples of living beings whose cells are capable of maintaining a constant shape.
Answer. The cells of plants and fungi, that is, those that have a cell wall, maintain a constant shape.
2. What are the functions of ribosomes?
Answer. The ribosome is the most important non-membrane organelle of a living cell, serving for the biosynthesis of protein from amino acids according to a given matrix based on genetic information provided by messenger RNA (mRNA).
3. What is cytoplasm?
Answer. The internal environment of the cell - the cytoplasm - is a complexly organized system, including the nucleus, membrane and non-membrane organelles, inclusions that are suspended in the hyaloplasm. The latter is a gel with a degree of viscosity that varies depending on the functional state of the cell.
Questions after §15
1. What functions does the cytoskeleton perform?
Answer. All eukaryotes have a complex support system in the cytoplasm - the cytoskeleton. It consists of three elements: microtubules, intermediate filaments and microfilaments.
Microtubules penetrate the entire cytoplasm and are hollow tubes with a diameter of 20–30 nm. Their walls are formed by specially twisted threads built from the protein tubulin. The assembly of microtubules from tubulin occurs in the cell center. Microtubules are strong and form the supporting framework of the cytoskeleton. Often they are positioned in such a way as to counteract the stretching and contraction of the cell. In addition to their mechanical function, microtubules also perform a transport function, participating in the transport of various substances through the cytoplasm.
Intermediate filaments are about 10 nm thick and are also protein in nature. Their functions are currently not well understood.
Microfilaments are protein filaments with a diameter of only 4 nm. Their basis is the protein actin. Sometimes actin filaments are grouped into bundles. Microfilaments are most often located close to the plasma membrane and are capable of changing its shape, which is very important, for example, for the processes of phagocytosis and pinocytosis.
Thus, the cytoplasm is permeated with cytoskeletal structures that maintain the shape of the cell and provide intracellular transport. The cytoskeleton can quickly “disassemble” and “assemble”. When it is assembled, organelles can move through its structures with the help of special proteins, getting to those places in the cell where they are needed at the moment.
2. What does the cell center consist of?
Answer. Cellular center (centrosome). It is located in the cytoplasm near the nucleus and is formed by two centrioles - cylinders located perpendicular to each other. The diameter of each centriole is 150–250 nm, and the length is 300–500 nm. The wall of each centriole consists of nine complexes of microtubules, and each complex (or triplet), in turn, is built of three microtubules. The triplets of the centriole are connected to each other by a series of ligaments. The main protein that forms centrioles is tubulin. Tubulin is transported to the cell center area through the cytoplasm. Here the cytoskeletal elements are assembled from this protein. Already assembled, they are sent to various parts of the cytoplasm, where they perform their functions.
Centrioles are also necessary for the formation of the basal bodies of cilia and flagella. Before cell division, the centrioles double. During the process of cell division, they diverge in pairs to opposite poles of the cell and participate in the formation of filaments of the spindle.
In the cells of higher plants, the cell center is structured differently and does not contain centrioles.
3. What process is carried out in ribosomes?
Answer. The organelles required by the cell for protein synthesis are ribosomes. Their size is approximately 20 x 30 nm; there are several million of them in a cell. Ribosomes consist of two subunits - large and small. Each subunit is a complex of rRNA with proteins. Ribosomes are formed in the region of the nucleoli of the nucleus, and then enter the cytoplasm through nuclear pores. They carry out protein synthesis, namely, the assembly of protein molecules from amino acids delivered to the tRNA ribosome. Between the subunits of the ribosome there is a gap in which the mRNA molecule is located, and on the large subunit there is a groove along which the synthesized protein molecule slides. Thus, in ribosomes the process of translation of genetic information is carried out, i.e., its translation from the “language of nucleotides” to the “language of amino acids”.
Ribosomes can be suspended in the cytoplasm, but more often they are located in groups on the surface of the endoplasmic reticulum of the cell. It is believed that free ribosomes synthesize proteins necessary for the needs of the cell itself, and ribosomes attached to the EPS produce proteins “for export,” that is, proteins that are intended for use in the extracellular space or in other cells of the body.
Cell– an elementary unit of a living system. Various structures of a living cell that are responsible for performing a particular function are called organelles, like the organs of a whole organism. Specific functions in the cell are distributed between organelles, intracellular structures that have a certain shape, such as the cell nucleus, mitochondria, etc.
Cellular structures:
Cytoplasm. An essential part of the cell, enclosed between the plasma membrane and the nucleus. Cytosol is a viscous aqueous solution of various salts and organic substances, permeated with a system of protein threads - cytoskeletons. Most chemical and physiological processes of the cell take place in the cytoplasm. Structure: Cytosol, cytoskeleton. Functions: includes various organelles, internal cell environment
Plasma membrane. Each cell of animals, plants, is limited from the environment or other cells by a plasma membrane. The thickness of this membrane is so small (about 10 nm) that it can only be seen with an electron microscope.
Lipids they form a double layer in the membrane, and proteins penetrate its entire thickness, are immersed to different depths in the lipid layer or are located on the outer and inner surfaces of the membrane. The structure of the membranes of all other organelles is similar to the plasma membrane. Structure: double layer of lipids, proteins, carbohydrates. Functions: restriction, preservation of cell shape, protection from damage, regulator of the intake and removal of substances.
Lysosomes. Lysosomes are membrane-bound organelles. They have an oval shape and a diameter of 0.5 microns. They contain a set of enzymes that destroy organic substances. The membrane of lysosomes is very strong and prevents the penetration of its own enzymes into the cytoplasm of the cell, but if the lysosome is damaged by any external influences, then the entire cell or part of it is destroyed.
Lysosomes are found in all cells of plants, animals and fungi.
By digesting various organic particles, lysosomes provide additional “raw materials” for chemical and energy processes in the cell. When cells are starved, lysosomes digest some organelles without killing the cell. This partial digestion provides the cell with the necessary minimum of nutrients for some time. Sometimes lysosomes digest entire cells and groups of cells, which plays a significant role in developmental processes in animals. An example is the loss of a tail when a tadpole transforms into a frog. Structure: oval vesicles, membrane outside, enzymes inside. Functions: breakdown of organic substances, destruction of dead organelles, destruction of spent cells.
Golgi complex. The biosynthetic products entering the lumens of the cavities and tubules of the endoplasmic reticulum are concentrated and transported in the Golgi apparatus. This organelle measures 5–10 μm.
Structure: cavities (bubbles) surrounded by membranes. Functions: accumulation, packaging, excretion of organic substances, formation of lysosomes
Endoplasmic reticulum. The endoplasmic reticulum is a system for the synthesis and transport of organic substances in the cytoplasm of a cell, which is an openwork structure of connected cavities.
Attached to the membranes of the endoplasmic reticulum are a large number of ribosomes - the smallest cell organelles, shaped like spheres with a diameter of 20 nm. and consisting of RNA and protein. Protein synthesis occurs on ribosomes. Then the newly synthesized proteins enter the system of cavities and tubules, through which they move inside the cell. Cavities, tubules, tubes from membranes, ribosomes on the surface of membranes. Functions: synthesis of organic substances using ribosomes, transport of substances.
Ribosomes. Ribosomes are attached to the membranes of the endoplasmic reticulum or are free in the cytoplasm, they are located in groups, and proteins are synthesized on them. Protein composition, ribosomal RNA Functions: ensures protein biosynthesis (assembly of a protein molecule from).
Mitochondria. Mitochondria are energy organelles. The shape of mitochondria is different; they can be other, rod-shaped, filamentous with an average diameter of 1 micron. and 7 µm long. The number of mitochondria depends on the functional activity of the cell and can reach tens of thousands in the flight muscles of insects. Mitochondria are bounded on the outside by an outer membrane, under which there is an inner membrane, forming numerous projections - cristae.
Inside mitochondria are RNA, DNA and ribosomes. Specific enzymes are built into its membranes, with the help of which the energy of nutrients is converted into ATP energy in the mitochondria, which is necessary for the life of the cell and the organism as a whole.
Membrane, matrix, outgrowths - cristae. Functions: synthesis of the ATP molecule, synthesis of its own proteins, nucleic acids, carbohydrates, lipids, formation of its own ribosomes.
Plastids. Only in plant cells: leucoplasts, chloroplasts, chromoplasts. Functions: accumulation of reserve organic substances, attraction of pollinating insects, synthesis of ATP and carbohydrates. Chloroplasts are shaped like a disk or ball with a diameter of 4–6 microns. With a double membrane - external and internal. Inside the chloroplast there are ribosome DNA and special membrane structures - grana, connected to each other and to the inner membrane of the chloroplast. Each chloroplast has about 50 grains, arranged in a checkerboard pattern to better capture light. Gran membranes contain chlorophyll, thanks to which the energy of sunlight is converted into the chemical energy of ATP. The energy of ATP is used in chloroplasts for the synthesis of organic compounds, primarily carbohydrates.
Chromoplasts. Red and yellow pigments found in chromoplasts give different parts of the plant their red and yellow colors. carrots, tomato fruits.
Leukoplasts are the site of accumulation of a reserve nutrient – starch. There are especially many leukoplasts in the cells of potato tubers. In the light, leucoplasts can turn into chloroplasts (as a result of which potato cells turn green). In autumn, chloroplasts turn into chromoplasts and green leaves and fruits turn yellow and red.
Cell center. Consists of two cylinders, centrioles, located perpendicular to each other. Functions: support for spindle threads
Cellular inclusions either appear in the cytoplasm or disappear during the life of the cell.
Dense, granular inclusions contain reserve nutrients (starch, proteins, sugars, fats) or cell waste products that cannot yet be removed. All plastids of plant cells have the ability to synthesize and accumulate reserve nutrients. In plant cells, storage of reserve nutrients occurs in vacuoles.
Grains, granules, drops Functions: non-permanent formations storing organic matter and energy
Core. Nuclear envelope of two membranes, nuclear juice, nucleolus. Functions: storage of hereditary information in the cell and its reproduction, synthesis of RNA - informational, transport, ribosomal. The nuclear membrane contains spores, through which active exchange of substances occurs between the nucleus and the cytoplasm. The nucleus stores hereditary information not only about all the characteristics and properties of a given cell, about the processes that should occur in it (for example, protein synthesis), but also about the characteristics of the organism as a whole. Information is recorded in DNA molecules, which are the main part of chromosomes. The nucleus contains a nucleolus. The nucleus, due to the presence of chromosomes containing hereditary information, functions as a center that controls all the life activity and development of the cell.
Cytoplasm is perhaps the most important part of any cellular 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 occurring in the smallest living structure at the macro level, where the main role is played by the gel-like mass that fills the internal volume of the cell and gives it its appearance and shape.
Cytoplasm is a viscous (jelly-like) transparent substance that fills each cell and is bounded by the cell membrane. It consists of water, salts, proteins and other organic molecules.
All organelles of eukaryotes, 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 cytosol. Although it may seem that the cytoplasm has neither shape nor structure, it is actually 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
Mainly the cytoplasm is the substance that fills the cell. This substance is viscous, gel-like, consists of 80% water and is usually clear and colorless.
Cytoplasm is the substance of life, also called molecular soup, in which cellular organelles are suspended and connected to each other by a bilayer lipid membrane. The cytoskeleton, located 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 was said, substance consists of 70−90% water and is colorless. Most cellular processes occur 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 cytoplasm around the vacuole.
Main characteristics
The following properties of the cytoplasm should be listed:
Structure and components
In prokaryotes (such as bacteria), which do not have a membrane-bound nucleus, 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 distinct components: the cytosol, organelles, and various particles and granules called cytoplasmic inclusions.
Cytosol, organelles, inclusions
The cytosol is a semi-liquid component located external to the nucleus and internal to the plasma membrane. The cytosol makes up approximately 70% of the cell volume and consists of water, cytoskeletal fibers, salts, and organic and inorganic molecules dissolved in water. 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 aggregates, which strongly influence the transfer of substances between the components of the cytoplasm.
Organoid means "small organ" that is associated with a membrane. Organelles are located inside the cell and perform specific functions necessary to maintain the life of this smallest building block of life. Organelles are small cellular structures that perform specialized functions. The following examples can be given:
- mitochondria;
- ribosomes;
- core;
- lysosomes;
- chloroplasts (in plants);
- endoplasmic reticulum;
- Golgi apparatus.
Inside the cell there is also a 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. Three types of such inclusions can be found: secretory, nutritious, and pigmented. Examples of secretory inclusions include proteins, enzymes and acids. Glycogen (the storage molecule for glucose) and lipids are prime examples of nutrient inclusions, and melanin found in skin cells is an example of pigment inclusions.
Cytoplasmic inclusions, being small particles suspended in the cytosol, represent a diverse range of inclusions present in different types of cells. These can be either crystals of calcium oxalate or silicon dioxide in plants, or granules of starch and glycogen. A wide range of inclusions are lipids that have a spherical shape, are present in both prokaryotes and eukaryotes, and serve 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 presented in the following table:
- ensuring the shape of the cell;
- habitat of organelles;
- transport of substances;
- supply of nutrients.
Cytoplasm serves to support organelles and cellular molecules. Many cellular processes occur in the cytoplasm. Some of these processes include protein synthesis, the first stage of cellular respiration, which is called glycolysis, processes of mitosis and meiosis. In addition, the cytoplasm helps hormones move throughout the cell, and waste products are also removed through it.
Most of the different actions and events take place in this gelatin-like liquid, which contains enzymes that promote the decomposition of waste products, and many metabolic processes also take place here. Cytoplasm provides the cell with shape, filling it, and helps maintain the organelles in their places. Without it, the cell would appear "deflated" and various substances could not easily move from one organelle to another.
Transport of substances
The liquid substance of the cell contents is very important for maintaining its vital functions, since allows easy exchange of nutrients between organelles. This exchange is due to the process of cytoplasmic flow, which is the flow of cytosol (the most mobile and fluid part of the cytoplasm) transporting nutrients, genetic information and other substances from one organelle to another.
Some of the processes that occur in the cytosol also include metabolite transfer. The organelle can produce amino acid, fatty acid and other substances, which move through the cytosol to the organelle that needs these substances.
Cytoplasmic flows lead to 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 cell to move through space). For other cells, for example, amoeba, the only way to move is the movement of fluid in the cytosol.
Nutrient supply
In addition to the transport of various materials, the liquid space between organelles acts as a kind of storage chamber for these materials until the moment when they are actually needed by one or another organelle. Proteins, oxygen, and various building blocks are suspended inside the cytosol. In addition to useful substances, the cytoplasm also contains metabolic products that wait their turn until the removal process removes them from the cell.
Plasma membrane
The cell, or plasma, membrane is a formation that prevents the flow of cytoplasm from the cell. This membrane is composed of phospholipids that form a lipid bilayer, which is semi-permeable: only certain molecules can penetrate this layer. Proteins, lipids, and other molecules can cross the cell membrane through the process of endocytosis, which produces a vesicle containing these substances.
A vesicle containing fluid and molecules breaks away from the membrane, forming an endosome. The latter moves inside the cell to its recipients. Waste products are eliminated through the process of exocytosis. In this process, vesicles formed in the Golgi apparatus connect to a membrane, which pushes their contents into the environment. The membrane also provides the cell with shape and serves as a supporting platform for the cytoskeleton and cell wall (in plants).
Plant and animal cells
The similarity of the internal contents of plant and animal cells indicates their similar origin. Cytoplasm provides mechanical support to the internal structures of the cell, which are suspended in it.
Cytoplasm maintains the shape and consistency of the cell and also contains many chemicals that are key to maintaining life processes and metabolism.
Metabolic reactions such as glycosis and protein synthesis occur in the jelly-like contents. In plant cells, unlike animal cells, there is a movement of 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 cytoskeleton.
