The structure and properties of the cytoplasm. What is cytoplasm? Functions of the cytoplasm in the cell

Today you can find out what cytoplasm is in biology. In addition, we offer to pay attention to many interesting questions:

1. Cell organization.
2. Hyaloplasm.
3. Properties and functions of the cytoplasm.
4. organelles and so on.

To begin with, we propose to introduce a definition for an unknown term. The cytoplasm is that part of the cell that is outside the nucleus and is limited by the membrane. The entire contents of the cell, including the nucleus, is protoplasm.

It is important to pay attention to the fact that it is here that important metabolic processes take place. In the cytoplasm occurs:

• absorption of ions and other metabolites;
• transportation;
• energy generation;
• synthesis of protein and non-protein products;
• cellular digestion and so on.

All of the above processes maintain cell viability.

Types of structural organization of the cell

It's no secret that all tissues and organs are formed from the smallest particles - cells.

Scientists were able to identify only two of their types:

• prokaryotic;
• eukaryotic.

The simplest forms of life contain a single cell and multiply by cell division. These two forms of cells have some differences and similarities. In prokaryotic cells, there is no nucleus, and the chromosome is located directly in the cytoplasm (what is the cytoplasm in biology was said earlier). This structure is present in bacteria. Another thing is the eukaryotic cell. We will talk about it in the next section.

eukaryotic cell

This species has a more complex structure. DNA is associated with protein and is located in the chromosomes, which, in turn, are located in the nucleus. This organelle is separated by a membrane. Despite the large number of differences, the cells have something in common - the internal contents are filled with a colloidal solution.

The cytoplasm of the cell (or colloidal solution) is an important constituent. It has a semi-liquid state. There we can also find:

• tubules;
• microtubules;
• microfilaments;
• filaments.

Cytoplasm is a colloidal solution in which the movement of colloidal particles and other components occurs. The solution itself consists of water and other compounds (both organic and inorganic). It is in the cytoplasm that organelles and temporary inclusions are located.

Differences between plant and animal cell cytoplasm

We have already introduced the definition of cytoplasm, now we will reveal the differences between the colloidal solution in animal and plant cells.

1. The cytoplasm of a plant cell. In its composition, we can find plastids, of which there are three types in total: chloroplasts, chromoplasts and leukoplasts.
2. The cytoplasm of an animal cell. In this case, we can observe two layers of cytoplasm - ectoplasm and endoplasm. The outer layer (ectoplasm) contains a huge amount of microfilament, and the inner layer contains organelles and granules. In this case, the endoplasm is less viscous.

Hyaloplasm

The basis of the cytoplasm of the cell is hyaloplasm. What it is? Hyaloplasm is a solution that is heterogeneous in composition, slimy and colorless. It is in this environment that metabolism takes place. The term "matrix" is often used in relation to hyaloplasm.

The composition includes:

• proteins;
• lipids;
• polysaccharides;
• nucleotides;
• amino acids;
• ions of inorganic compounds.

Hyaloplasm is represented by two forms:

• gel;
• sol.

There are mutual transitions between these two phases.

Substances of the colloidal solution of the cell

What is the cytoplasm in biology, we have already explained, now we propose to proceed to the consideration of the chemical composition of the colloidal solution. All substances that make up the cell can be divided into two broad groups:

• organic;
• inorganic.

The first group contains:

• proteins;
• carbohydrates (monosaccharides, disaccharides and polysaccharides);
• fats;
• nucleic acids.

A little more about carbohydrates. Monosaccharides - fructose, glucose, ribose and others. Large polysaccharides consist of monosaccharides - starch, glycogen and cellulose.

• water (ninety percent);
• oxygen;
• hydrogen;
• carbon;
• nitrogen;
• sodium;
• calcium;
• sulfur;
• chlorine and so on.

Properties of the cytoplasm

Speaking about what cytoplasm is in biology, one cannot ignore the question of the properties of a colloidal solution.

The first and very important feature is cyclosis. In other words, it is the movement that takes place inside the cell. If this movement stops, the cell immediately dies. The rate of cyclosis directly depends on some factors, such as:

• light;
• temperature and so on.

The second property is viscosity. This indicator varies depending on the organism. The viscosity of the cytoplasm directly depends on the metabolism.

The third feature is semipermeability. The presence of boundary membranes in the cytoplasm allows some molecules to pass through, while others are retained. This selective permeability plays an important role in the life of the cell.

Organelles of the cytoplasm

All organelles that make up the cell can be divided into two groups.

1. Membrane. These are closed cavities (vacuole, sac, cistern). They got this name because the contents of the organoid are separated from the cytoplasm by a membrane. Moreover, all membrane organelles can be further divided into two groups: single-membrane and double-membrane. The first include the endoplasmic reticulum, the Golgi complex, lysosomes, peroxisomes. It is important to note that all single-membrane organelles are interconnected and create a single system. Two-membrane organelles include mitochondria and plastids. They have a complex structure, and two membranes separate them from the cytoplasm.
2. Non-membrane. These include fibrillar structures and ribosomes. The former include microfilaments, microfibrils and microtubules.

In addition to organelles, the cytoplasm includes inclusions.

Functions of the cytoplasm

The functions of the cytoplasm include:

• filling the cell area;
• binding of cellular components;
• combining the components of the cell into a single whole;
• determining the position of organelles;
• conductor for chemical and physical processes;
• maintenance of internal pressure in the cell, volume, elasticity.

As you can see, the importance of the cytoplasm is very great for all cells, both eukaryotic and prokaryotic.

The concept of cytoplasm was introduced as early as 1882. It is known that the cytoplasm is the internal environment of the cell. In this article, we will consider what the cytoplasm is, what is included in its structure and what is its content.

We will also answer the question of what functions the cytoplasm performs.

The concept of cytoplasm

Cytoplasm is commonly understood as the internal environment of a living or dead cell. The cytoplasm does not include the nucleus and vacuoles. The cytoplasm includes hyaloplasm, which is a transparent substance and organelles, it also includes the so-called inclusions. The inclusion is called various non-permanent structures, for example, they include the waste products of the cell, various secrets, pigments.

The composition of the cytoplasm

The structure of the cytoplasm is a combination of organic and inorganic substances. The main substance of which the cytoplasm is composed is water. The cytoplasm also contains true and colloidal solutions. The true solution is formed by mineral salts, glucose and amino acids. Colloidal solution contains proteins. Also in the structure of the cytoplasm, insoluble waste products and nutrient reserves can be found.

Functions of the cytoplasm

The most important functions of the cytoplasm are the unification of cellular structures, as well as ensuring their interaction. In addition, the cytoplasm, due to constant movement and flow within the cell, ensures the movement of various substances, which contributes to the nutrition of all organelles and organelles. It also provides turgor (stress state) of the cell.

Cytoplasm - the contents of the cell outside the nucleus, enclosed in the plasma membrane. It has a transparent color and a gel-like consistency. The cytoplasm consists mainly of water, and also contains enzymes, salts, and various organic molecules.

Function of the cytoplasm

The cytoplasm functions to support and suspend organelles and cellular molecules. Many cellular processes also take place in the cytoplasm.

Some of these processes include protein synthesis, the first step known as glycolysis, and . In addition, the cytoplasm helps move substances such as hormones around the cell and also dissolves cellular waste.

Components of the cytoplasm

Organelles

Organelles are tiny cellular structures that perform specific functions within the cell. Examples of organelles include: , and .

Also inside the cytoplasm is a network of fibers that help the cell maintain its shape and provide support for the organelles.

Cytoplasmic inclusions

Cytoplasmic inclusions are particles temporarily suspended in the cytoplasm. Inclusions consist of macromolecules and granules.

The three types of inclusions found in the cytoplasm are secretory and nutrient inclusions, and pigment granules. Examples of secretory inclusions are proteins, enzymes and acids. Glycogen (storage of glucose molecules) and lipids are examples of nutrient inclusions. The melanin present in skin cells is an example of the incorporation of pigment granules.

Cytoplasmic divisions

Cytoplasm can be divided into two main parts: endoplasm and ectoplasm. Endoplasm is the central region of the cytoplasm that contains organelles. Ectoplasm is the more gel-like peripheral portion of the cell's cytoplasm.

cell membrane

The cell or plasma membrane is a structure that prevents the cytoplasm from spilling out of the cell. This membrane is composed of phospholipids that form a lipid bilayer that separates the contents of the cell from the extracellular fluid. The lipid bilayer is semi-permeable, meaning that only some molecules are able to diffuse across the membrane to enter or exit the cell. Extracellular fluid, proteins, lipids and other molecules can be added to the cytoplasm of the cell with the help of. In this process, molecules and extracellular fluid are internalized as the membrane forms a vesicle.

The vesicle separates fluid, molecules, and kidneys from the cell membrane, forming an endosome. The endosome moves within the cell to deliver its contents to the appropriate destinations. Substances are removed from the cytoplasm by. In this process, vesicles budded from the Golgi bodies fuse with the cell membrane, forcing their contents out of the cell. The plasma membrane also provides structural support to the cell, acting as a stable platform for the attachment of the cytoskeleton and .

1. Prokaryotes and eukaryotes
2. Cytoplasm. biological membranes.
3. Types of cell nutrition.
4. non-membrane organelles.

1. Eukaryotes and prokaryotes.

Eukaryotic cells, characterized by diversity and complexity of structure, have common features. Each cell consists of two important, inextricably linked parts - the cytoplasm and the nucleus, as well as the membrane that limits the cell.

Prokaryotic cells, which include bacteria, unlike eukaryotes, have a relatively simple structure. A prokaryotic cell does not have an organized nucleus; it contains only one chromosome, which is not separated from the rest of the cell by a membrane, but lies directly in the cytoplasm. However, it also contains all the hereditary information of a bacterial cell.

The cytoplasm of prokaryotes compared to the cytoplasm of eukaryotic cells is much poorer in terms of the composition of the structures. There are numerous smaller ribosomes than in eukaryotic cells. The functional role of mitochondria and chloroplasts in prokaryotic cells is performed by special, rather simply organized membrane folds.

Prokaryotic cells, like eukaryotic cells, are covered with a plasma membrane, on top of which there is a cell membrane or mucous capsule. Despite their relative simplicity, prokaryotes are typical independent cells. Comparative characteristics of eukaryotic cells. Different eukaryotic cells are structurally similar. But along with the similarities between the cells of organisms of various kingdoms of living nature, there are noticeable differences. They concern both structural and biochemical features.

A plant cell is characterized by the presence of various plastids, a large central vacuole, which sometimes pushes the nucleus to the periphery, and a cell wall located outside the plasma membrane, consisting of cellulose. In the cells of higher plants, there is no centriole in the cell center, which is found only in algae. The reserve nutrient carbohydrate in plant cells is starch.

Comparative characteristics of prokaryotes and eukaryotes

In the cells of representatives of the kingdom of fungi, the cell wall usually consists of chitin - the substance from which the external skeleton of arthropods and animals is built. There is a central vacuole, no plastids. Only some fungi have a centriole in the cell center. The storage carbohydrate in fungal cells is glycogen.

In animal cells, there is no dense cell wall, no plastids. There is no central vacuole in the animal cell. The centriole is characteristic of the cell center of animal cells. Glycogen is also a reserve carbohydrate in animal cells.

prokaryotes

These are all bacteria, cyanobacteria, or blue-green, as well as archaebacteria. The analogue of the nucleus in prokaryotes is a structure consisting of DNA, having the shape of a ring and immersed in the cytoplasm. DNA is not connected to histones, so all the genes that make up the chromosomes of prokaryotes are working, that is, information is continuously read from them. A prokaryotic cell is surrounded by a membrane separating the cytoplasm from the cell wall (in bacteria, cyanide). Cell walls in prokaryotes have a peculiar structure that differs from those of eukaryotes. Many prokaryotes have glycopeptide and murein in their cell walls. There are few membranes in the cytoplasm; they represent an invagination of the outer cytoplasmic membrane. There are no organelles: mitochondria, chloroplasts, centrioles, Golgi apparatus. Protein synthesis is carried out by ribosomes smaller than those of eukaryotes. All enzymes that provide vital processes are diffusely dispersed in the cytoplasm or attached to the inner surface of the cytoplasmic membrane.

Nucleoid(lat. nucleus - nucleus and Greek eidos - view) - a DNA-containing zone of a prokaryotic cell. Sometimes the nucleoid is called the bacterial chromosome.

2. Cytoplasm- the internal cellular environment, which makes up the entire contents of the cell. Liquid phase of the cytoplasm - cytosol is a complex of organic and inorganic compounds dissolved in water. The cytosol can be liquid or gel-like (gelatinous). All cellular organelles or organelles are immersed in the cytosol - permanent cell structures, as well as non-permanent cellular formations - inclusions: reserve nutrients and products to be excreted. In the cytoplasm there is a system of filaments (filaments) that connects individual cell structures with each other and with the plasma membrane. Of the three types of filaments (myosin filaments, microfilaments, microtubules), the last two form a complex, which is a cell frame - cytoskeleton. It gives the cell shape and serves as a site for attachment of organelles, while at the same time it is a mobile, changing structure.

Functions of the cytoplasm: unification of all cellular structures into a single interacting complex; place of deposition of spare substances; the environment for the flow of various biochemical processes characteristic of a given cell.

Organelles are located in the cytoplasm, which are divided into membrane and non-membrane.

biological membranes. The basis of the structural organization of the cell is the membrane principle of structure. Membranes form many organelle structures that are found in the cytoplasm. All biological membranes have a similar structure: two rows of phospholipids, in which molecules of various proteins are immersed at different depths, some of the proteins can penetrate the membrane through. The thickness of the biological membrane is 7.5-8 nm. Most of the immersed proteins are enzymes, they determine the nature of biochemical reactions. The protein components of the membranes that form the various organelles of the cytoplasm are not the same. So, the membranes that form mitochondria include enzymes involved in the synthesis of ATP, etc.

cytoplasmic or plasma membrane plasmalemma- the most important organelle of the cell, separates the cytoplasm of the cell from the external environment or membrane (in plant cells). It forms the surface of the cell, has the same structure as all biological membranes. Due to numerous outgrowths, the membrane significantly increases the area of ​​contact with the environment surrounding the cell.

3 Functions of the cytoplasmic membrane:

- protective - delimits the internal contents of the cell from the external environment;

- security interconnection of cells due to the formation of intercellular contacts;

- regulatory - carries out an exchange between the cell and the environment due to the active or passive entry of substances into the cell based on selective permeability;

- receptor - associated with the localization of special structures on the cytoplasmic membrane - sets of receptors (glycoproteins can act as such receptors);

- energy transforming - consists in converting electrical energy into chemical energy;

- transport - the membrane carries out the transfer of substances into the cell as a result of the interaction of peripheral and integral proteins. The membrane has pores through which water and some ions passively enter the cell. Active transfer of substances into the cell - endocytosis - is carried out with the help of special molecules that make up the cytoplasmic membrane. Endocytosis occurs in the form of phagocytosis and pinocytosis.

3 Types of cell nutrition.

Phagocytosis(Greek phagos - to devour and cytos - cell) - the capture of solid particles by the cytoplasmic membrane and invagination, drawing them into the cell. The edges of the invagination close, the vacuole with particles or molecules of solids is immersed in the cytoplasm and laces off.

pinocytosis(Greek pino - drink and cytos - cell) - similar in mechanism to phagocytosis, the capture of various liquids by the membrane.

Phagocytosis and pinocytosis are carried out in a similar way and differ only in the amount of substances absorbed on the cell surface. These processes are associated with energy consumption. If ATP synthesis is disturbed in the cell, then phagocytosis and pinocytosis are inhibited.

Exocytosis- removal of hormones, polysaccharides, proteins, fat drops, etc. from the cell by the formation of membrane vesicles in the cytoplasm and the release of these substances into the environment surrounding the cell.

1. Non-membrane organelles: ribosomes and cell center.

Usually, cell center found in animal cells and located near the nucleus. It is formed centrioles- two small cylindrical bodies located at a right angle. Centrioles are self-replicating cell organelles. The cell center plays an important role in cell division.

Ribosomes- spherical particles with a diameter of 15.0-35.0 nm, consisting of two unequal parts - subunits. They are synthesized in the nucleus, then leave it, passing into the cytoplasm, where they are attached to the outer surface of the membranes of the endoplasmic reticulum or are located freely. Depending on the type of protein being synthesized, ribosomes can function alone or combine into complexes - polyribosomes.

Membrane organelles (organelles) of the cell are separate or interconnected structures, the contents of which are separated from the liquid contents of the cell (cytosol) by a membrane or membranes.

Cytoplasm- an obligatory part of the cell, enclosed between the plasma membrane and the nucleus; It is subdivided into hyaloplasm (the main substance of the cytoplasm), organelles (permanent components of the cytoplasm) and inclusions (temporary components of the cytoplasm). The chemical composition of the cytoplasm: the basis is water (60-90% of the total mass of the cytoplasm), various organic and inorganic compounds. The cytoplasm is alkaline. A characteristic feature of the cytoplasm of a eukaryotic cell is constant movement ( cyclosis). It is detected primarily by the movement of cell organelles, such as chloroplasts. If the movement of the cytoplasm stops, the cell dies, since only being in constant motion can it perform its functions.

Hyaloplasm ( cytosol) is a colorless, slimy, thick and transparent colloidal solution. It is in it that all metabolic processes take place, it provides the interconnection of the nucleus and all organelles. Depending on the predominance of the liquid part or large molecules in the hyaloplasm, two forms of hyaloplasm are distinguished: sol- more liquid hyaloplasm and gel- denser hyaloplasm. Mutual transitions are possible between them: the gel turns into a sol and vice versa.

Functions of the cytoplasm:

1. integration of all components of the cell into a single system,
2. environment for the passage of many biochemical and physiological processes,
3. environment for the existence and functioning of organelles.

Cell walls

Cell walls limit eukaryotic cells. In each cell membrane, at least two layers can be distinguished. The inner layer is adjacent to the cytoplasm and is represented by plasma membrane(synonyms - plasmalemma, cell membrane, cytoplasmic membrane), over which the outer layer is formed. In an animal cell, it is thin and is called glycocalyx(formed by glycoproteins, glycolipids, lipoproteins), in a plant cell - thick, called cell wall(formed by cellulose).

All biological membranes have common structural features and properties. Currently generally accepted fluid mosaic model of the membrane structure. The basis of the membrane is a lipid bilayer, formed mainly by phospholipids. Phospholipids are triglycerides in which one fatty acid residue is replaced by a phosphoric acid residue; the section of the molecule in which the residue of phosphoric acid is located is called the hydrophilic head, the sections in which fatty acid residues are located are called hydrophobic tails. In the membrane, phospholipids are arranged in a strictly ordered manner: the hydrophobic tails of the molecules face each other, and the hydrophilic heads face outwards, towards the water.

In addition to lipids, the membrane contains proteins (on average ≈ 60%). They determine most of the specific functions of the membrane (transport of certain molecules, catalysis of reactions, receiving and converting signals from the environment, etc.). Distinguish: 1) peripheral proteins(located on the outer or inner surface of the lipid bilayer), 2) semi-integral proteins(immersed in the lipid bilayer to different depths), 3) integral or transmembrane proteins(permeate the membrane through and through, while in contact with both the external and internal environment of the cell). Integral proteins in some cases are called channel-forming, or channel, since they can be considered as hydrophilic channels through which polar molecules pass into the cell (the lipid component of the membrane would not let them through).

A - hydrophilic head of the phospholipid; C, hydrophobic tails of the phospholipid; 1 - hydrophobic regions of proteins E and F; 2, hydrophilic regions of protein F; 3 - a branched oligosaccharide chain attached to a lipid in a glycolipid molecule (glycolipids are less common than glycoproteins); 4 - branched oligosaccharide chain attached to a protein in a glycoprotein molecule; 5 - hydrophilic channel (functions as a pore through which ions and some polar molecules can pass).

The membrane may contain carbohydrates (up to 10%). The carbohydrate component of membranes is represented by oligosaccharide or polysaccharide chains associated with protein molecules (glycoproteins) or lipids (glycolipids). Basically, carbohydrates are located on the outer surface of the membrane. Carbohydrates provide receptor functions of the membrane. In animal cells, glycoproteins form an epimembrane complex, the glycocalyx, several tens of nanometers thick. Many cell receptors are located in it, with its help cell adhesion occurs.

Molecules of proteins, carbohydrates and lipids are mobile, able to move in the plane of the membrane. The thickness of the plasma membrane is approximately 7.5 nm.

Membrane functions

The membranes perform the following functions:

1. separation of cellular contents from the external environment,
2. regulation of metabolism between the cell and the environment,
3. division of the cell into compartments ("compartments"),
4. location of "enzymatic conveyors",
5. providing communication between cells in the tissues of multicellular organisms (adhesion),
6. signal recognition.

The most important membrane property- selective permeability, i.e. membranes are highly permeable to some substances or molecules and poorly permeable (or completely impermeable) to others. This property underlies the regulatory function of membranes, which ensures the exchange of substances between the cell and the external environment. The process by which substances pass through the cell membrane is called transport of substances. Distinguish: 1) passive transport- the process of passing substances, going without energy; 2) active transport- the process of passing substances, going with the cost of energy.

At passive transport substances move from an area with a higher concentration to an area with a lower one, i.e. along the concentration gradient. In any solution there are molecules of the solvent and the solute. The process of movement of solute molecules is called diffusion, the movement of solvent molecules is called osmosis. If the molecule is charged, then its transport is affected by the electrical gradient. Therefore, one often speaks of an electrochemical gradient, combining both gradients together. The speed of transport depends on the magnitude of the gradient.

The following types of passive transport can be distinguished: 1) simple diffusion- transport of substances directly through the lipid bilayer (oxygen, carbon dioxide); 2) diffusion through membrane channels- transport through channel-forming proteins (Na +, K +, Ca 2+, Cl -); 3) facilitated diffusion- transport of substances using special transport proteins, each of which is responsible for the movement of certain molecules or groups of related molecules (glucose, amino acids, nucleotides); 4) osmosis- transport of water molecules (in all biological systems, water is the solvent).

Necessity active transport occurs when it is necessary to ensure the transfer of molecules through the membrane against the electrochemical gradient. This transport is carried out by special carrier proteins, the activity of which requires energy expenditure. The energy source is ATP molecules. Active transport includes: 1) Na + /K + -pump (sodium-potassium pump), 2) endocytosis, 3) exocytosis.

Work Na + /K + -pump. For normal functioning, the cell must maintain a certain ratio of K + and Na + ions in the cytoplasm and in the external environment. The concentration of K + inside the cell should be significantly higher than outside it, and Na + - vice versa. It should be noted that Na + and K + can freely diffuse through the membrane pores. The Na+/K+ pump counteracts the equalization of these ion concentrations and actively pumps Na+ out of the cell and K+ into the cell. The Na + /K + -pump is a transmembrane protein capable of conformational changes, so that it can attach both K + and Na + . The cycle of operation of Na + /K + -pump can be divided into the following phases: 1) attachment of Na + from the inside of the membrane, 2) phosphorylation of the pump protein, 3) release of Na + in the extracellular space, 4) attachment of K + from the outside of the membrane , 5) dephosphorylation of the pump protein, 6) release of K + in the intracellular space. The sodium-potassium pump consumes almost a third of all the energy necessary for the life of the cell. During one cycle of operation, the pump pumps out 3Na + from the cell and pumps in 2K +.

Endocytosis- the process of absorption by the cell of large particles and macromolecules. There are two types of endocytosis: 1) phagocytosis- capture and absorption of large particles (cells, cell parts, macromolecules) and 2) pinocytosis- capture and absorption of liquid material (solution, colloidal solution, suspension). The phenomenon of phagocytosis was discovered by I.I. Mechnikov in 1882. During endocytosis, the plasma membrane forms an invagination, its edges merge, and the structures delimited from the cytoplasm by a single membrane are laced into the cytoplasm. Many protozoa and some leukocytes are capable of phagocytosis. Pinocytosis is observed in the epithelial cells of the intestine, in the endothelium of blood capillaries.

Exocytosis- the reverse process of endocytosis: the removal of various substances from the cell. During exocytosis, the vesicle membrane fuses with the outer cytoplasmic membrane, the contents of the vesicle are removed outside the cell, and its membrane is included in the outer cytoplasmic membrane. In this way, hormones are excreted from the cells of the endocrine glands, and in protozoa, undigested food remains.

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