The cell is the basic structural and functional unit of all living organisms, except viruses. It has a specific structure, including many components that perform specific functions.
What science studies the cell?
Everyone knows that the science of living organisms is biology. The structure of a cell is studied by its branch - cytology.
What does a cell consist of?
This structure consists of a membrane, cytoplasm, organelles, or organelles, and a nucleus (absent in prokaryotic cells). The structure of cells of organisms belonging to different classes, varies slightly. Significant differences are observed between the cell structure of eukaryotes and prokaryotes.
Plasma membrane
The membrane plays a very important role - it separates and protects the contents of the cell from external environment. It consists of three layers: two protein layers and a middle phospholipid layer.
Cell wall
Another structure that protects the cell from exposure external factors, located on top plasma membrane. Present in the cells of plants, bacteria and fungi. In the first it consists of cellulose, in the second - from murein, in the third - from chitin. In animal cells, a glycocalyx is located on top of the membrane, which consists of glycoproteins and polysaccharides.
Cytoplasm
It represents the entire cell space limited by the membrane, with the exception of the nucleus. The cytoplasm includes organelles that perform the main functions responsible for the life of the cell.
Organelles and their functions
The structure of a cell of a living organism involves a number of structures, each of which performs a specific function. They are called organelles, or organelles.
Mitochondria
They can be called one of the most important organelles. Mitochondria are responsible for the synthesis of energy necessary for life. In addition, they are involved in the synthesis of certain hormones and amino acids.
Energy in mitochondria is produced due to the oxidation of ATP molecules, which occurs with the help of a special enzyme called ATP synthase. Mitochondria are round or rod-shaped structures. Their number in animal cell, on average, is 150-1500 pieces (this depends on its purpose). They consist of two membranes and a matrix - a semi-liquid mass that fills the internal space of the organelle. The main components of the shells are proteins; phospholipids are also present in their structure. The space between the membranes is filled with liquid. The mitochondrial matrix contains grains that accumulate certain substances, such as magnesium and calcium ions, necessary for energy production, and polysaccharides. Also, these organelles have their own protein biosynthesis apparatus, similar to that of prokaryotes. It consists of mitochondrial DNA, a set of enzymes, ribosomes and RNA. The structure of a prokaryotic cell has its own characteristics: it does not contain mitochondria.
Ribosomes
These organelles are composed of ribosomal RNA (rRNA) and proteins. Thanks to them, translation is carried out - the process of protein synthesis on an mRNA (messenger RNA) matrix. One cell can contain up to ten thousand of these organelles. Ribosomes consist of two parts: small and large, which combine directly in the presence of mRNA.
Ribosomes, which are involved in the synthesis of proteins necessary for the cell itself, are concentrated in the cytoplasm. And those with the help of which proteins are produced that are transported outside the cell are located on the plasma membrane.
Golgi complex
It is present only in eukaryotic cells. This organelle consists of dictosomes, the number of which is usually approximately 20, but can reach several hundred. The Golgi apparatus is included in the cell structure of only eukaryotic organisms. It is located near the nucleus and performs the function of synthesis and storage of certain substances, for example, polysaccharides. It produces lysosomes, which we'll talk below. This organelle is also part excretory system cells. Dictosomes are presented in the form of stacks of flattened disc-shaped cisterns. At the edges of these structures, vesicles form, containing substances that need to be removed from the cell.
Lysosomes
These organelles are small vesicles containing a set of enzymes. Their structure has one membrane covered with a layer of protein on top. The function performed by lysosomes is the intracellular digestion of substances. Thanks to the enzyme hydrolase, with the help of these organelles, fats, proteins, carbohydrates, and nucleic acids are broken down.
Endoplasmic reticulum (reticulum)
The cell structure of all eukaryotic cells also implies the presence of EPS (endoplasmic reticulum). The endoplasmic reticulum consists of tubes and flattened cavities with a membrane. This organelle comes in two types: rough and smooth network. The first is distinguished by the fact that ribosomes are attached to its membrane, the second does not have this feature. Rough endoplasmic reticulum performs the function of synthesizing proteins and lipids that are required for the formation of the cell membrane or for other purposes. Smooth takes part in the production of fats, carbohydrates, hormones and other substances, except proteins. The endoplasmic reticulum also performs the function of transporting substances throughout the cell.
Cytoskeleton
It consists of microtubules and microfilaments (actin and intermediate). The components of the cytoskeleton are polymers of proteins, mainly actin, tubulin or keratin. Microtubules serve to maintain the shape of the cell; they form organs of movement in simple organisms, such as ciliates, chlamydomonas, euglena, etc. Actin microfilaments also play the role of a framework. In addition, they are involved in the process of organelle movement. Intermediates in different cells are built from different proteins. They maintain the shape of the cell and also secure the nucleus and other organelles in a constant position.
Cell center
Consists of centrioles, which have the shape of a hollow cylinder. Its walls are formed from microtubules. This structure is involved in the process of division, ensuring the distribution of chromosomes between daughter cells.
Core
In eukaryotic cells it is one of the most important organelles. It stores DNA, which encrypts information about the entire organism, its properties, proteins that must be synthesized by the cell, etc. It consists of a shell that protects the genetic material, nuclear sap (matrix), chromatin and the nucleolus. The shell is formed from two porous membranes located at some distance from each other. The matrix is represented by proteins; it forms a favorable environment inside the nucleus for storing hereditary information. The nuclear sap contains filamentous proteins that serve as support, as well as RNA. Also present here is chromatin, an interphase form of chromosome existence. During cell division, it turns from clumps into rod-shaped structures.
Nucleolus
This is a separate part of the nucleus responsible for the formation of ribosomal RNA.
Organelles found only in plant cells
Plant cells have some organelles that are not characteristic of any other organisms. These include vacuoles and plastids.
Vacuole
This is a kind of reservoir where reserve nutrients are stored, as well as waste products that cannot be removed due to the dense cell wall. It is separated from the cytoplasm by a specific membrane called the tonoplast. As the cell functions, individual small vacuoles merge into one large one - the central one.
Plastids
These organelles are divided into three groups: chloroplasts, leucoplasts and chromoplasts.
Chloroplasts
These are the most important organelles of a plant cell. Thanks to them, photosynthesis occurs, during which the cell receives the nutrients it needs. nutrients. Chloroplasts have two membranes: outer and inner; matrix - the substance that fills the internal space; own DNA and ribosomes; starch grains; grains. The latter consist of stacks of thylakoids with chlorophyll, surrounded by a membrane. It is in them that the process of photosynthesis occurs.
Leukoplasts
These structures consist of two membranes, a matrix, DNA, ribosomes and thylakoids, but the latter do not contain chlorophyll. Leukoplasts perform a reserve function, accumulating nutrients. They contain special enzymes that make it possible to obtain starch from glucose, which, in fact, serves as a reserve substance.
Chromoplasts
These organelles have the same structure as those described above, however, they do not contain thylakoids, but there are carotenoids that have a specific color and are located directly next to the membrane. It is thanks to these structures that flower petals are painted a certain color, allowing them to attract pollinating insects.
Most living organisms have a cellular structure. A cell is a structural and functional unit of living things. It is characterized by all the signs and functions of living organisms: metabolism and energy, growth, reproduction, self-regulation. Cells vary in shape, size, functions, and type of metabolism (Fig. 47).
Rice. 47. Diversity of cells: 1 - green euglena; 2 - bacteria; 3 - plant cell of the leaf pulp; 4 - epithelial cell; 5 - nerve cell
Cell sizes vary from 3-10 to 100 µm (1 µm = 0.001 m). Cells smaller than 1-3 microns in size are less common. There are also giant cells, the size of which reaches several centimeters. The shape of the cells is also very diverse: spherical, cylindrical, oval, spindle-shaped, stellate, etc. However, all cells have much in common. They have the same chemical composition And overall plan buildings.
Chemical composition of the cell. Of all the known chemical elements About 20 are found in living organisms, and 4 of them: oxygen, carbon, hydrogen and nitrogen account for up to 95%. These elements are called biogenic elements. From inorganic substances that are part of living organisms, highest value has water. Its content in the cell ranges from 60 to 98%. In addition to water, the cell also contains minerals, mainly in the form of ions. These are compounds of iron, iodine, chlorine, phosphorus, calcium, sodium, potassium, etc.
In addition to inorganic substances, the cell also contains organic matter: proteins, lipids (fats), carbohydrates (sugars), nucleic acids (DNA, RNA). They make up the bulk of the cell. The most important organic substances are nucleic acids and proteins. Nucleic acids (DNA and RNA) are involved in the transmission of hereditary information, protein synthesis, and regulation of all cell life processes.
Squirrels perform a number of functions: construction, regulatory, transport, contractile, protective, energy. But the most important is the enzymatic function of proteins.
Enzymes- these are biological catalysts that accelerate and regulate all the diversity chemical reactions occurring in living organisms. Not a single reaction in a living cell occurs without the participation of enzymes.
Lipids And carbohydrates They perform mainly construction and energy functions and are reserve nutrients for the body.
So, phospholipids together with proteins they build all membrane structures of the cell. A high molecular weight carbohydrate, cellulose forms the cell wall of plants and fungi.
Fats, starch And glycogen are reserve nutrients for the cell and the body as a whole. Glucose, fructose, sucrose and others Sahara are part of the roots, leaves, and fruits of plants. Glucose is an obligatory component of the blood plasma of humans and many animals. When carbohydrates and fats are broken down in the body, a large amount of energy is released, which is necessary for vital processes.
Cellular structures. The cell consists of an outer cell membrane, cytoplasm with organelles and a nucleus (Fig. 48).
Rice. 48. Combined diagram of the structure of an animal (A) and plant (B) cell: 1 - shell; 2 - outer cell membrane; 3 - core; 4 - chromatin; 5 - nucleolus; 6 - endoplasmic reticulum (smooth and granular); 7 - mitochondria; 8 - chloroplasts; 9 - Golgi apparatus; 10 - lysosome; 11 - cell center; 12 - ribosomes; 13 - vacuole; 14 - cytoplasm
Outer cell membrane- this is a single membrane cellular structure, which limits the living contents of the cell of all organisms. Possessing selective permeability, it protects the cell, regulates the flow of substances and exchange with the external environment, and maintains a certain cell shape. Cells of plant organisms and fungi, in addition to the membrane on the outside, also have a membrane. This non-living cellular structure consists of cellulose in plants and chitin in fungi, gives strength to the cell, protects it, and is the “skeleton” of plants and fungi.
IN cytoplasm, The semi-liquid contents of the cell contain all the organelles.
Endoplasmic reticulum penetrates the cytoplasm, providing communication between individual parts of the cell and transport of substances. There are smooth and granular EPS. Ribosomes are located on the granular ER.
Ribosomes- These are small mushroom-shaped bodies on which protein synthesis occurs in the cell.
Golgi apparatus ensures packaging and removal of synthesized substances from the cell. In addition, from its structures are formed lysosomes. These spherical bodies contain enzymes that break down nutrients entering the cell, providing intracellular digestion.
Mitochondria- These are semi-autonomous membrane structures of elongated shape. Their number in cells varies and increases as a result of division. Mitochondria are the energy stations of the cell. During the process of respiration, the final oxidation of substances with atmospheric oxygen occurs. In this case, the released energy is stored in ATP molecules, the synthesis of which occurs in these structures.
Chloroplasts, semi-autonomous membrane organelles, are characteristic only of plant cells. Chloroplasts are green in color due to the pigment chlorophyll; they provide the process of photosynthesis.
In addition to chloroplasts, plant cells also have vacuoles, filled with cell sap.
Cell center participates in the process of cell division. It consists of two centrioles and a centrosphere. During division, they form filaments of the spindle and provide uniform distribution chromosomes in a cell.
Core- This is the center for regulating the life of the cell. The nucleus is separated from the cytoplasm by a nuclear membrane, which has pores. Inside it is filled with karyoplasm, which contains DNA molecules that ensure the transmission of hereditary information. Here the synthesis of DNA, RNA, and ribosomes occurs. Often one or more dark round formations can be seen in the nucleus - these are nucleoli. Ribosomes are formed and accumulated here. In the nucleus, DNA molecules are not visible, as they are in the form of thin strands of chromatin. Before division, DNA spirals, thickens, forms complexes with protein and turns into clearly visible structures - chromosomes (Fig. 49). Usually the chromosomes in a cell are paired, identical in shape, size and hereditary information. Paired chromosomes are called homologous. A double paired set of chromosomes is called diploid. Some cells and organisms contain a single, unpaired set called haploid.
Rice. 49. A - chromosome structure: 1 - centromere; 2 - chromosome arms; 3 - DNA molecules; 4 - sister chromatids; B - types of chromosomes: 1 - equal-armed; 2 - different shoulders; 3 - single-shoulder
The number of chromosomes for each type of organism is constant. Thus, in human cells there are 46 chromosomes (23 pairs), in wheat cells there are 28 (14 pairs), and in pigeons there are 80 (40 pairs). These organisms contain a diploid set of chromosomes. Some organisms, such as algae, mosses, and fungi, have a haploid set of chromosomes. Sex cells in all organisms are haploid.
In addition to those listed, some cells have specific organelles - cilia And flagella, providing movement mainly in unicellular organisms, but they are also present in some cells multicellular organisms. For example, flagella are found in Euglena green, Chlamydomonas, and some bacteria, and cilia are found in ciliates, the cells of the ciliated epithelium of animals.
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§ 43. Basic criteria for living things§ 45. Features of cell activity
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All living beings and organisms do not consist of cells: plants, fungi, bacteria, animals, people. Despite its minimal size, all the functions of the whole organism are performed by the cell. Complex processes take place inside it, on which the vitality of the body and the functioning of its organs depend.
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Structural features
Scientists are studying structural features of the cell and the principles of its work. A detailed examination of the structural features of a cell is possible only with the help of a powerful microscope.
All our tissues - skin, bones, internal organs consist of cells that are construction material, there are different forms and sizes, each variety performs a specific function, but the main features of their structure are similar.
First let's find out what's behind it structural organization of cells. In the course of their research, scientists have found that the cellular foundation is membrane principle. It turns out that all cells are formed from membranes, which consist of a double layer of phospholipids, with outer and inside protein molecules are immersed.
What property is characteristic of all types of cells: the same structure, as well as functionality - regulation of the metabolic process, use of their own genetic material (presence and RNA), receipt and consumption of energy.
The structural organization of the cell is based on the following elements that perform a specific function:
- membrane- cell membrane, consists of fats and proteins. Its main task is to separate substances inside from the external environment. The structure is semi-permeable: it can also transmit carbon monoxide;
- core– central area and main component, separated from other elements by a membrane. It is inside the nucleus that there is information about growth and development, genetic material, presented in the form of DNA molecules that make up the composition;
- cytoplasm- this is a liquid substance that forms the internal environment where various vital processes take place and contains many important components.
What does the cellular content consist of, what are the functions of the cytoplasm and its main components:
- Ribosome- the most important organelle that is necessary for the processes of biosynthesis of proteins from amino acids; proteins perform great amount vital tasks.
- Mitochondria- another component located inside the cytoplasm. It can be described in one phrase – an energy source. Their function is to provide components with power for further energy production.
- Golgi apparatus consists of 5 - 8 bags that are connected to each other. The main task of this apparatus is to transfer proteins to other parts of the cell to provide energy potential.
- Damaged elements are cleaned lysosomes.
- Handles transportation endoplasmic reticulum, through which proteins move molecules of useful substances.
- Centrioles are responsible for reproduction.
Core
Since it is the cellular center, therefore, attention should be paid to its structure and functions Special attention. This component is the most important element for all cells: contains hereditary characteristics. Without the nucleus, the processes of reproduction and transmission of genetic information would become impossible. Look at the picture depicting the structure of the nucleus.
- The nuclear membrane, which is highlighted in lilac, lets the necessary substances in and releases them back through the pores - small holes.
- Plasma is a viscous substance and contains all other nuclear components.
- the core is located in the very center and has the shape of a sphere. His main function– formation of new ribosomes.
- If we consider central part cells in cross-section, you can see subtle blue weaves - chromatin, the main substance, which consists of a complex of proteins and long strands of DNA that carry the necessary information.
Cell membrane
Let's take a closer look at the work, structure and functions of this component. Below is a table that clearly shows the importance of the outer shell.
Chloroplasts
This is another most important component. But why weren’t chloroplasts mentioned earlier, you ask? Yes, because this component is found only in plant cells. The main difference between animals and plants is the method of nutrition: in animals it is heterotrophic, and in plants it is autotrophic. This means that animals are not able to create, that is, synthesize organic substances from inorganic ones - they feed on ready-made organic substances. Plants, on the contrary, are capable of carrying out the process of photosynthesis and contain special components - chloroplasts. These are green plastids containing the substance chlorophyll. With its participation, light energy is converted into the energy of chemical bonds of organic substances.
Interesting! Chloroplasts are concentrated in large quantities mainly in the above-ground parts of plants - green fruits and leaves.
If you are asked a question: tell me important feature buildings organic compounds cells, then the answer can be given as follows.
- many of them contain carbon atoms, which have different chemical and physical properties, and are also able to connect with each other;
- are carriers, active participants in various processes occurring in organisms, or are their products. This refers to hormones, various enzymes, vitamins;
- can form chains and rings, which provides a variety of connections;
- are destroyed when heated and interacting with oxygen;
- atoms within molecules are combined with each other using covalent bonds, do not decompose into ions and therefore interact slowly, reactions between substances take a very long time - several hours and even days.
Structure of chloroplast
Fabrics
Cells can exist one at a time, as in unicellular organisms, but most often they unite in groups of their own kind and form various tissue structures that make up the organism. There are several types of tissues in the human body:
- epithelial– concentrated on the surface skin, organs, elements of the digestive tract and respiratory system;
- muscular— we move thanks to the contraction of the muscles of our body, we carry out a variety of movements: from the simplest movement of the little finger to high-speed running. By the way, the heartbeat also occurs due to the contraction of muscle tissue;
- connective tissue makes up up to 80 percent of the mass of all organs and plays a protective and supporting role;
- nervous- forms nerve fibers. Thanks to it, various impulses pass through the body.
Reproduction process
Throughout the life of an organism, mitosis occurs - this is the name given to the process of division. consisting of four stages:
- Prophase. The cell's two centrioles divide and move in opposite directions. At the same time, the chromosomes form pairs, and the nuclear shell begins to collapse.
- The second stage is called metaphases. The chromosomes are located between the centrioles, and gradually the outer shell of the nucleus completely disappears.
- Anaphase is the third stage, during which the centrioles continue to move in the opposite direction from each other, and individual chromosomes also follow the centrioles and move away from each other. The cytoplasm and the entire cell begin to shrink.
- Telophase– final stage. The cytoplasm contracts until two identical new cells appear. A new membrane is formed around the chromosomes and one pair of centrioles appears in each new cell.
Interesting! Epithelial cells divide faster than those of bone tissue. It all depends on the density of the fabrics and other characteristics. Average duration The life of the main structural units is 10 days.
Cell structure. Cell structure and functions. Cell life.
Conclusion
You learned what the structure of a cell is - the most important component of the body. Billions of cells make up an amazingly wisely organized system that ensures the performance and vital activity of all representatives of the animal and plant world.
Cells are divided into prokaryotic and eukaryotic. The first are algae and bacteria, which contain genetic information in a single organelle, the chromosome, while eukaryotic cells, which make up more complex organisms such as the human body, have a clearly differentiated nucleus, which contains several chromosomes with genetic material.
Eukaryotic cell
Prokaryotic cell
Structure
Cell or cytoplasmic membrane
The cytoplasmic membrane (envelope) is fine structure, which separates the contents of the cell from environment. It consists of a double layer of lipids with protein molecules approximately 75 angstroms thick.
Cell membrane It is continuous, but it has numerous folds, convolutions, and pores, which allows you to regulate the passage of substances through it.
Cells, tissues, organs, systems and devices
Cells, Human body- a component of elements that act harmoniously to effectively perform all vital functions.
Textile- these are cells of the same shape and structure, specialized to perform the same function. Various tissues combine to form organs, each of which performs a specific function in a living organism. In addition, organs are also grouped into a system to perform a specific function.
Fabrics:
Epithelial- protects and covers the surface of the body and internal surfaces of organs.
Connective- fat, cartilage and bone. Performs various functions.
Muscular- smooth muscle, striated muscle tissue. Contracts and relaxes muscles.
Nervous- neurons. Generates and transmits and receives impulses.
Cell size
The size of the cells varies greatly, although they generally range from 5 to 6 microns (1 micron = 0.001 mm). This explains the fact that many cells could not see before the invention electron microscope, the resolution of which ranges from 2 to 2000 angstroms (1 angstrom = 0.000 000 1 mm). The size of some microorganisms is less than 5 microns, but there are also giant cells. The most famous is the yolk of bird eggs, an egg cell about 20 mm in size.
There are even more striking examples: the cell of acetabularia, a single-celled marine algae, reaches 100 mm, and ramie, a herbaceous plant, reaches 220 mm - more than the palm of your hand.
From parents to children thanks to chromosomes
The cell nucleus undergoes various changes when the cell begins to divide: the membrane and nucleoli disappear; At this time, chromatin becomes more dense, eventually forming thick threads - chromosomes. A chromosome consists of two halves - chromatids, connected at a constriction site (centrometre).
Our cells, like all animal and plant cells, obey the so-called law of numerical constancy, according to which the number of chromosomes of a certain type is constant.
In addition, chromosomes are distributed in pairs that are identical to each other.
Each cell in our body contains 23 pairs of chromosomes, which are several elongated DNA molecules. The DNA molecule takes the form of a double helix, consisting of two sugar phosphate groups, from which nitrogenous bases (purines and pyramidines) protrude in the form of steps of a spiral staircase.
Along each chromosome there are genes responsible for heredity, the transmission of genetic characteristics from parents to children. They determine the color of the eyes, skin, shape of the nose, etc.
Mitochondria
Mitochondria are round or elongated organelles distributed throughout the cytoplasm, containing a watery solution of enzymes that are capable of carrying out numerous chemical reactions, such as cellular respiration.
Through this process, the energy that the cell needs to perform its vital functions is released. Mitochondria are mainly found in the most active cells living organisms: pancreatic and liver cells.
Cell nucleus
Core, one in each human cell, is its main component, since it is an organism that controls the functions of the cell and a carrier of hereditary characteristics, which proves its importance in reproduction and the transmission of biological heredity.
In the core, the size of which ranges from 5 to 30 microns, the following elements can be distinguished:
- Nuclear envelope. It is double and allows substances to pass between the nucleus and the cytoplasm due to its porous structure.
- Nuclear plasma. A light, viscous liquid in which the remaining nuclear structures are immersed.
- Nucleolus. A spherical body, isolated or in groups, involved in the formation of ribosomes.
- Chromatin. A substance that can take on different colors, consisting of long strands of DNA (deoxyribonucleic acid). Threads are particles, genes, each of which contains information about a specific cell function.
Nucleus of a typical cell
Skin cells live on average one week. Red blood cells live 4 months, and bone cells live from 10 to 30 years.
Centrosome
The centrosome is usually located near the nucleus and plays vital role in mitosis, or cell division.
It consists of 3 elements:
- Diplosoma. It consists of two centrioles - cylindrical structures located perpendicularly.
- Centrosphere. A translucent substance in which the diplosome is immersed.
- Aster. A radiant formation of filaments emerging from the centosphere, having important for mitosis.
Golgi complex, lysosomes
The Golgi complex consists of 5-10 flat disks (plates), in which the main element is distinguished - the tank and several dictyosomes, or a cluster of tanks. These dictyosomes are separated and distributed evenly during mitosis, or cell division.
Lysosomes, the “stomach” of the cell, are formed from vesicles of the Golgi complex: they contain digestive enzymes, which allow them to digest food entering the cytoplasm. Their interior, or mycus, is lined with a thick layer of polysaccharides that prevent these enzymes from breaking down their own cellular material.
Ribosomes
Ribosomes are cellular organelles with a diameter of about 150 angstroms that are attached to the membranes of the endoplasmic reticulum or are freely located in the cytoplasm.
They consist of two subunits:
- the large subunit consists of 45 protein molecules and 3 RNA (ribonucleic acid);
- the smaller subunit consists of 33 protein molecules and 1 RNA.
Ribosomes are combined into polysomes using an RNA molecule and synthesize proteins from amino acid molecules.
Cytoplasm
Cytoplasm is an organic mass located between the cytoplasmic membrane and the nuclear envelope. Contains the internal environment - hyaloplasm - a viscous liquid consisting of a large amount of water and containing proteins, monosaccharides and fats in dissolved form.
It is part of a cell endowed with vital activity because various cellular organelles move inside it and biochemical reactions occur. Organelles perform the same role in a cell as organs do in human body: produce vital substances, generate energy, perform the functions of digestion and excretion of organic substances, etc.
About a third of the cytoplasm is water.
In addition, the cytoplasm contains 30% organic substances (carbohydrates, fats, proteins) and 2-3% inorganic substances.
Endoplasmic reticulum
The endoplasmic reticulum is a network-like structure formed by the folding of the cytoplasmic envelope into itself.
This process, known as intussusception, is thought to have led to more complex creatures with greater protein requirements.
Depending on the presence or absence of ribosomes in the membranes, two types of networks are distinguished:
1. The endoplasmic reticulum is folded. A set of flat structures interconnected and communicating with the nuclear membrane. A large number of ribosomes are attached to it, so its function is to accumulate and release proteins synthesized in ribosomes.
2. The endoplasmic reticulum is smooth. A network of flat and tubular elements that communicates with the folded endoplasmic reticulum. Synthesizes, secretes and transports fats throughout the cell, along with the proteins of the folded reticulum.
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As you know, almost all organisms on our planet have a cellular structure. Basically, all cells have a similar structure. It is the smallest structural and functional unit of a living organism. Cells can have different functions, and, consequently, variations in their structure. In many cases they can act as independent organisms.
Cellular structure have plants, animals, fungi, bacteria. However, there are some differences between their structural and functional units. And in this article we will look at the cellular structure. Grade 8 involves studying this topic. Therefore, the article will be of interest to schoolchildren, as well as those who are simply interested in biology. This review will describe various organisms, the similarities and differences between them.
History of the theory of cellular structure
People did not always know what organisms were made of. It became known relatively recently that all tissues are formed from cells. The science that studies this is biology. The cellular structure of the body was first described by scientists Matthias Schleiden and Theodor Schwann. This happened in 1838. Then the structure consisted of the following provisions:
animals and plants of all kinds are formed from cells;
they grow through the formation of new cells;
cell is the smallest unit of life;
An organism is a collection of cells.
Modern theory includes slightly different provisions, and there are a little more of them:
a cell can only come from a mother cell;
It does not consist of a simple collection of cells, but of those united into tissues, organs and organ systems;
the cells of all organisms have a similar structure;
cell - a complex system, consisting of smaller functional units;
cell - the smallest structural unit, capable of acting as an independent organism.
Cell structure
Since almost all living organisms have a cellular structure, it is worth considering general characteristics structure of this element. Firstly, all cells are divided into prokaryotic and eukaryotic. The latter contain a nucleus that protects the hereditary information recorded on DNA. In prokaryotic cells it is absent, and the DNA floats freely. All are built according to following diagram. They have a shell - a plasma membrane, around which additional protective formations are usually located. Everything underneath it, except the nucleus, is cytoplasm. It consists of hyaloplasm, organelles and inclusions. Hyaloplasm is the main transparent substance that serves internal environment cells and fills all its space. Organelles are permanent structures, which perform certain functions, i.e., ensure the vital activity of the cell. Inclusions are non-permanent formations that also play one role or another, but do so temporarily.
Cellular structure of living organisms
Now we will list the organelles that are the same for the cells of any living creature on the planet, except bacteria. These are mitochondria, ribosomes, Golgi apparatus, endoplasmic reticulum, lysosomes, cytoskeleton. Bacteria are characterized by only one of these organelles - ribosomes. Now let's look at the structure and functions of each organelle separately.
Mitochondria
They provide intracellular respiration. Mitochondria play the role of a kind of “power station”, producing energy that is necessary for the life of the cell, for the passage of certain chemical reactions in it.
They belong to double-membrane organelles, that is, they have two protective shells - external and internal. Below them is a matrix - an analogue of hyaloplasm in a cell. Cristae form between the outer and inner membranes. These are folds that contain enzymes. These substances are needed in order to be able to carry out chemical reactions that release the energy needed by the cell.
Ribosomes
They are responsible for protein metabolism, namely, for the synthesis of substances of this class. Ribosomes consist of two parts - subunits, large and small. This organelle does not have a membrane. Ribosomal subunits are combined only immediately before the process of protein synthesis; the rest of the time they are separate. Substances here are produced based on information recorded on DNA. This information is delivered to the ribosomes using tRNA, since transporting DNA here every time would be very impractical and dangerous - the likelihood of its damage would be too high.
Golgi apparatus
This organelle consists of stacks of flat cisternae. The functions of this organelle are that it accumulates and modifies various substances, and also participates in the process of lysosome formation.
Endoplasmic reticulum
It is divided into smooth and rough. The first one is built from flat tubes. It is responsible for the production of steroids and lipids in the cell. Rough is called so because there are numerous ribosomes on the walls of the membranes of which it is composed. It performs a transport function. Namely, it transfers proteins synthesized there from ribosomes to the Golgi apparatus.
Lysosomes
They are substances that contain enzymes necessary to carry out chemical reactions that occur during intracellular metabolism. The largest number of lysosomes is observed in leukocytes - cells that perform immune function. This is explained by the fact that they carry out phagocytosis and are forced to digest foreign protein, which requires a large volume of enzymes.
Cytoskeleton
This is the last organelle that is common to fungi, animals and plants. One of its main functions is to maintain the shape of the cell. It is formed from microtubules and microfilaments. The first are hollow tubes made of the protein tubulin. Due to their presence in the cytoplasm, some organelles can move throughout the cell. In addition, cilia and flagella in unicellular organisms can also consist of microtubules. The second component of the cytoskeleton, microfilaments, consists of the contractile proteins actin and myosin. In bacteria, this organelle is usually absent. But some of them are characterized by the presence of a cytoskeleton, but it is more primitive, not as complex as that of fungi, plants and animals.
Plant cell organelles
The cellular structure of plants has some features. In addition to the organelles listed above, vacuoles and plastids are also present. The former are designed to accumulate substances in it, including unnecessary ones, since it is often impossible to remove them from the cell due to the presence of a dense wall around the membrane. The fluid that is inside the vacuole is called cell sap. The young one initially has several small vacuoles, which merge into one large one as it ages. Plastids are divided into three types: chromoplasts, leucoplasts and chromoplasts. The former are characterized by the presence of red, yellow or orange pigment. Chromoplasts in most cases are needed to attract bright color pollinating insects or animals that participate in the distribution of fruits along with seeds. It is thanks to these organelles that flowers and fruits have a variety of colors. Chromoplasts can be formed from chloroplasts, which can be observed in the fall, when the leaves acquire yellow-red hues, as well as when the fruits ripen, when the color gradually disappears completely. green color. The next type of plastid - leucoplasts - are designed to store substances such as starch, some fats and proteins. Chloroplasts carry out the process of photosynthesis, through which plants obtain the necessary organic substances for themselves.
From six molecules of carbon dioxide and the same amount of water, a cell can receive one molecule of glucose and six oxygen, which is released into the atmosphere. Chloroplasts are double-membrane organelles. Their matrix contains thylakoids grouped into grana. These structures contain chlorophyll, and this is where the photosynthesis reaction takes place. In addition, the chloroplast matrix also contains its own ribosomes, RNA, DNA, special enzymes, starch grains and lipid droplets. The matrix of these organelles is also called stroma.
Features of mushrooms
These organisms also have a cellular structure. In ancient times they were united into one kingdom with plants purely according to external sign, however, with the advent of more developed science, it became clear that this could not be done.
Firstly, mushrooms, unlike plants, are not autotrophs; they are not capable of producing organic substances themselves, but only feed on ready-made ones. Secondly, a fungal cell is more similar to an animal cell, although it has some plant features. The cell of a fungus, just like a plant, is surrounded by a dense wall, but it consists not of cellulose, but of chitin. This substance is difficult for animals to digest, which is why mushrooms are considered heavy food. In addition to the organelles described above, which are characteristic of all eukaryotes, there is also a vacuole - this is another similarity between fungi and plants. But plastids are not observed in the structure of the fungal cell. Between the wall and the cytoplasmic membrane there is a losomesome, the functions of which are still not fully understood. Otherwise, the structure of a mushroom cell resembles that of an animal cell. In addition to organelles, inclusions such as fat drops and glycogen also float in the cytoplasm.
Animal cells
They are characterized by all the organelles that were described at the beginning of the article. In addition, located on top of the plasma membrane is the glycocalyx, a membrane consisting of lipids, polysaccharides and glycoproteins. It is involved in the transport of substances between cells.
Core
Of course, in addition to common organelles, animal, plant, and fungal cells have a nucleus. It is protected by two shells that have pores. The matrix consists of karyoplasm (nuclear juice), in which chromosomes float with hereditary information recorded on them. There are also nucleoli, which are responsible for the formation of ribosomes and RNA synthesis.
Prokaryotes
These include bacteria. The cellular structure of bacteria is more primitive. They don't have a core. The cytoplasm contains organelles such as ribosomes. Surrounding the plasma membrane is a cell wall made of murein. Most prokaryotes are equipped with organelles of movement - mainly flagella. An additional protective shell, a mucous capsule, can also be located around the cell wall. In addition to the main DNA molecules, in the cytoplasm of bacteria there are plasmids on which information is recorded that is responsible for increasing the body’s resistance to unfavorable conditions.
Are all organisms made of cells?
Some believe that all living organisms have a cellular structure. But this is not true. There is such a kingdom of living organisms as viruses.
They are not made of cells. This organism is represented by a capsid - a protein shell. Inside it is DNA or RNA, on which a small amount of genetic information is recorded. A lipoprotein shell, called a supercapsid, can also be located around the protein shell. Viruses can only reproduce inside foreign cells. In addition, they are capable of crystallization. As you can see, the statement that all living organisms have a cellular structure is incorrect.
comparison table
Now that we have looked at the structure of various organisms, let us summarize. So, cellular structure, table:
| Animals | Plants | Mushrooms | Bacteria | |
| Core | Eat | Eat | Eat | No |
| Cell wall | No | Yes, made from cellulose | Yes, from chitin | Yes, from murein |
| Ribosomes | Eat | Eat | Eat | Eat |
| Lysosomes | Eat | Eat | Eat | No |
| Mitochondria | Eat | Eat | Eat | No |
| Golgi apparatus | Eat | Eat | Eat | No |
| Cytoskeleton | Eat | Eat | Eat | Eat |
| Endoplasmic reticulum | Eat | Eat | Eat | No |
| Cytoplasmic membrane | Eat | Eat | Eat | Eat |
| Additional shells | Glycocalyx | No | No | Mucous capsule |
That's probably all. We looked at the cellular structure of all organisms that exist on the planet.
