What is an organelle? Structure and functions of organoids. Organa of the plant cell. Organic Animal Cells

A cell is a level of organization of living matter, an independent biosystem that has the basic properties of all living things. So, it can develop, reproduce, move, adapt and change. In addition, any cells are characterized by a metabolism, a specific structure, the orderliness of structures and functions.

Science, which deals with the study of cells, is cytology. Its subject are the structural units of multicellular animals and plants, single-celled organisms - bacteria, protozoa and algae, consisting of only one cell.

If we talk about the general organization of structural units of living organisms, they consist of a shell and a nucleus with a nucleolus. Also in their composition are cell organelles, cytoplasm. To date, a variety of research methods are highly developed, but the leading place is occupied by microscopy, which allows studying the structure of cells and investigating its basic structural elements.

What is an organelle?

Organoids (they are also called organelles) are permanent constituent elements of any cell that make it whole and perform certain functions. These are the structures that are vital for the maintenance of its activities.

Organoids include the nucleus, lysosomes, endoplasmic reticulum and the Golgi complex, vacuoles and vesicles, mitochondria, ribosomes, and the cell center (centrosome). This also includes the structures that form the cytoskeleton cells (microtubules and microfilaments), melanosomes. Separately it is necessary to allocate organoids of movement. These are cilia, flagella, myofibrils and pseudopods.

All these structures are interrelated and ensure the coordinated activity of cells. That is why the question: "What is an organoid?" - You can answer that it is a component that can be equated to the organ of a multicellular organism.

Classification of organelles

Cells differ in size and shape, as well as their functions, but they have a similar chemical structure and a unified principle of organization. At the same time, the question of what an organoid is and what structures it is is rather controversial. For example, lysosomes or vacuoles sometimes do not belong to cellular organelles.

If we talk about the classification of these cell components, then nemembrannye and membrane organoids are isolated. Nemembrannye - a cell center and ribosomes. Organoids of movement (microtubules and microfilaments) are also devoid of membranes.

At the heart of the structure of membrane organelles is the presence of a biological membrane. Single-membrane and bi-membrane organoids have a shell with a single structure, which consists of a double layer of phospholipids and protein molecules. It separates the cytoplasm from the external environment, helps the cell to keep its shape. It is worth remembering that in plant cells, in addition to the membrane, there is also an external cellulose membrane, which is called the cell wall. It performs a supporting function.

Membrane organelles include EPS, lysosomes and mitochondria, as well as lysosomes and plastids. Their membranes can differ only in the set of proteins.

If we talk about the functional capacity of organelles, some of them are able to synthesize certain substances. So, the important organoids of synthesis are mitochondria, in which ATP is formed. Ribosomes, plastids (chloroplasts) and a rough endoplasmic reticulum are responsible for the synthesis of proteins, smooth EPS - for the synthesis of lipids and carbohydrates.

Consider the structure and functions of organoids in more detail.

Core

This organelle is extremely important, because when it is removed cells cease to function and die.

The core has a double membrane, in which there are many pores. With the help of them, it is closely associated with the endoplasmic reticulum and cytoplasm. This organelle contains chromatin - chromosomes, which are a complex of proteins and DNA. Given this, we can say that it is the nucleus that is the organelle that is responsible for preserving the bulk of the genome.

The liquid part of the nucleus is called karyoplasm. It contains the products of the vital activity of nuclear structures. The most dense zone is the nucleolus, which contains ribosomes, complex proteins and RNA, as well as phosphates of potassium, magnesium, zinc, iron and calcium. The nucleolus disappears before cell division and is formed again in the last stages of this process.

Endoplasmic reticulum (reticulum)

EPS is a single-membrane organelle. It occupies half the volume of the cell and consists of tubules and cisterns that are connected together, as well as with the cytoplasmic membrane and the outer shell of the nucleus. The membrane of this organoid has the same structure as the plasmalome. This structure is holistic and does not open into the cytoplasm.

The endoplasmic reticulum is smooth and granular (rough). On the inner shell of granular EPS are placed ribosomes, in which the synthesis of proteins. On the surface of the smooth endoplasmic reticulum there are no ribosomes, but here the synthesis of carbohydrates and fats is carried out.

All substances that form in the endoplasmic reticulum are transported through the system of tubules and tubules to the destinations where they accumulate and subsequently are used in various biochemical processes.

Given the synthesizing ability of EPS, the roughened reticulum is located in cells whose main function is the formation of proteins, and the smooth function in cells that synthesize carbohydrates and fats. In addition, calcium ions are accumulated in the smooth reticulum, which are necessary for the normal functioning of cells or the organism as a whole.

It should also be noted that EPS is the location of the Golgi apparatus.

Lysosomes, their functions

Lysosomes are cellular organoids, which are represented by single-membrane round shaped sacs with hydrolytic and digestive enzymes (proteases, lipases and nuclease). The content of lysosomes is characterized by an acidic medium. Membranes of these formations isolate them from the cytoplasm, preventing the destruction of other structural components of the cells. When the enzymes of the lysosome are released into the cytoplasm, self-destruction of the cell occurs - autolysis.

It should be noted that enzymes are primarily synthesized on a rough endoplasmic reticulum, after which they are transferred to the Golgi apparatus. Here they undergo a modification, are packed into membrane vesicles and begin to separate, becoming independent components of the cell - lysosomes, which are primary and secondary.

Primary lysosomes are structures that separate from the Golgi apparatus, and secondary (digestive vacuoles) are those that result from the fusion of primary lysosomes and endocytosis vacuoles.

Given such a structure and organization, it is possible to single out the main functions of lysosomes:

• Digestion of various substances inside the cell;
• Destruction of cellular structures that are not needed;
• Participation in the processes of cell reorganization.

Vacuoles

Vacuoles are single-membrane organelles of spherical form, which are reservoirs of water and organic and inorganic compounds dissolved in it. The formation of these structures involves the Golgi apparatus and EPS.

There are few vacuoles in the animal cell. They are small and occupy no more than 5% of the volume. Their main role is to ensure the transport of substances throughout the cell.

Vacuoles of plant cells are large and occupy up to 90% of the volume. In a mature cell, there is only one vacuole, which occupies a central position. Its membrane is called tonoplast, and the contents are called cellular juice. The main functions of plant vacuoles are to ensure the tension of the cell membrane, the accumulation of various compounds and waste cells. In addition, these plant cell organelles supply the water necessary for the process of photosynthesis.

If we talk about the composition of the cell sap, then it includes the following substances:

• Reserve - organic acids, carbohydrates and proteins, individual amino acids;
• Compounds that are formed during the life of cells and accumulate in them (alkaloids, tannins and phenols);
• Phytoncides and phytohormones;
• Pigments, due to which fruits, root crops and petals of colors are painted in the appropriate color.

Golgi Complex

The structure of organoids called "Golgi apparatus" is quite simple. In plant cells they look like separate bodies with a membrane, in the cells of animals they are represented by cisterns, tubules and blisters. The structural unit of the Golgi complex is a diktiosome, which is represented by a stack of 4-6 "cisterns" and small vesicles, which are separated from them and are an intracellular transport system, and can also serve as a source of lysosomes. The number of diktiosomes can range from one to several hundred.

The Golgi complex, as a rule, is located near the core. In animal cells - near the cell center. The main functions of these organelles are the following:

• Secretion and accumulation of proteins, lipids and saccharides;
• Modification of organic compounds entering the Golgi complex;
• This organoid is the site of the formation of lysosomes.

It should be noted that EPS, lysosomes, vacuoles, and also the Golgi apparatus together form a tubular-vacuolar system, which divides the cell into separate regions with corresponding functions. In addition, this system provides a permanent update of the membranes.

Mitochondria are cell power stations

Mitochondria are two-membrane organoids of rod-shaped, globular or filiform shape that synthesize ATP. They have an outer smooth surface and an inner membrane with numerous folds, which are called cristae. It should be noted that the number of cristae in mitochondria can vary depending on the cell's need for energy. It is on the inner membrane that numerous enzyme complexes synthesizing adenosine triphosphate are concentrated. Here, the energy of the chemical bonds is converted into the macroergic bonds of ATP. In addition, in the mitochondria splits fatty acids and carbohydrates with the release of energy, which accumulates and is used for growth and synthesis.

The internal environment of these organelles is called a matrix. It contains ring DNA and RNA, small ribosomes. Interestingly, mitochondria are semi-autonomous organoids, because they depend on the functioning of the cell, but at the same time they can retain a certain independence. So, they are able to synthesize their own proteins and enzymes, and also to reproduce independently.

It is believed that the mitochondria originated when the aerobic prokaryotic organisms entered the host cell, which led to the formation of a specific symbiotic complex. Thus, mitochondrial DNA has the same structure as the DNA of modern bacteria, and the synthesis of proteins in both mitochondria and bacteria is inhibited by identical antibiotics.

Plastids are plant cell organelles

Plastids are quite large organelles. They are present only in plant cells and are formed from precursors - proplastids, contain DNA. These organelles play an important role in metabolism and are separated from the cytoplasm by a double membrane. In addition, they can form an ordered system of internal membranes.

Plastids come in three types:

1. Chloroplasts are the most numerous plastids responsible for photosynthesis, in which organic compounds and free oxygen are formed. These structures have a complex structure and are capable of moving in the cytoplasm towards the light source. The main substance that is contained in chloroplasts is chlorophyll, through which plants can use the energy of the sun. It should be noted that chloroplasts like mitochondria are semi-autonomous structures, since they are capable of independent division and synthesis of their own proteins.
2. Leukoplast - colorless plastids, which under the influence of light turn into chloroplasts. These cellular components contain enzymes. With their help, glucose is converted and accumulates in the form of starch grains. In some plants, these plastids are able to accumulate lipids or proteins in the form of crystals and amorphous bodies. The greatest number of leukoplasts is concentrated in the cells of the underground organs of plants.
3. Chromoplasts are derivatives of the other two kinds of plastids. They form carotenoids (with the destruction of chlorophyll), which have a red, yellow or orange color. Chromoplasts are the final stage of plastid transformation. Most of them in fruits, petals and autumn leaves.

Ribosomes

What is an organoid called a ribosome? Ribosomes are called non-membrane organelles, consisting of two fragments (small and large subunits). Their diameter is about 20 nm. They are found in all types of cells. They are organelles of animals and plant cells, bacteria. These structures form in the nucleus, after which they pass into the cytoplasm, where they are placed freely or attached to the EPS. Depending on the synthesizing properties, the ribosomes function alone or combine into complexes, forming polyribosomes. In this case, these non-membrane organelles are bound by an information RNA molecule.

The ribosome contains 4 molecules of r-RNA that make up its framework, as well as various proteins. The main task of this organoid is the collection of a polypeptide chain, which is the first stage in the synthesis of proteins. Those proteins that are formed by the ribosomes of the endoplasmic reticulum can be used by the whole organism. Proteins for the needs of an individual cell are synthesized by ribosomes, which are located in the cytoplasm. It should be noted that ribosomes are also found in mitochondria and plastids.

Cytoskeleton cells

The cellular cytoskeleton is formed by microtubules and microfilaments. Microtubules are cylindrical formations with a diameter of 24 nm. Their length is 100 μm-1 mm. The main component is a protein called tubulin. It is incapable of contraction and can be destroyed by colchicine. Microtubules are located in the hyaloplasm and perform the following functions:

• Create an elastic, but at the same time, a strong cell frame that allows it to retain its shape;
• Participate in the process of chromosome distribution of the cell;
• Provide the movement of organelles;
• Are contained in the cellular center, as well as in flagella and cilia.

Microfilaments are threads that are placed under the plasma membrane and consist of an actin or myosin protein. They can contract, resulting in the movement of the cytoplasm or protrusion of the cell membrane. In addition, these components are involved in the formation of a constriction in cell division.

The cell center (centrosome)

This organelle consists of 2 centrioles and a centrosphere. The centriole is cylindrical. Its walls are formed by three microtubules that merge with each other through cross-linking. Centrioles are arranged in pairs at right angles to each other. It should be noted that cells of higher plants are deprived of these organoids.

The main role of the cell center is to ensure an even distribution of chromosomes during cell division. He is also the center of the organization of the cytoskeleton.

Organelles of movement

To organoids of movement carry cilia, and also flagella. These are miniature outgrowths in the form of hairs. The flagella contains 20 microtubules. Its base is located in the cytoplasm and is called the basal body. The length of the flagellum is 100 μm or more. Flagellites, which have only 10-20 microns, are called cilia. When slipping microtubules, cilia and flagella are able to oscillate, causing the movement of the cell itself. The cytoplasm can contain contractile fibrils, which are called myofibrils - they are the organoids of the animal cell. Myofibrils, as a rule, are located in myocytes - cells of the muscle tissue, as well as in the heart cells. They consist of smaller fibers (protofibrils).

It should be noted that the beams of myofibrils consist of dark fibers - these are anisotropic discs, as well as light areas - is isotropic discs. The structural unit of the myofibril is the sarcomere. This is the area between the anisotropic and isotropic disk, which has actin and myosin filaments. When they slip, the sarcomere shrinks, which leads to the movement of the entire muscle fiber. In this case, the energy of ATP and calcium ions is used.

With the help of flagella, the simplest and spermatozoa of animals move. Cilia are the organ of movement of the infusoria-shoe. In animals and humans, they cover the airway respiratory tract and help to get rid of small solid particles, for example, from dust. In addition, there are still pseudopods that provide amoeboid movement and are the elements of many unicellular and animal cells (eg, leukocytes).

Most plants can not move in space. Their movements consist in growth, movement of leaves and changes in the cytoplasm of cells.

Conclusion

Despite the diversity of cells, they all have a similar structure and organization. The structure and functions of organoids are characterized by identical properties, ensuring the normal functioning of both the individual cell and the whole organism.

This regularity can be expressed as follows.

Table "Organoids of the eukaryote cell"

Organoid	Plant cell	Animal Cell	Main functions
core	there is	there is	DNA storage, RNA transcription and protein synthesis
Endoplasmic reticulum	there is	there is	Synthesis of proteins, lipids and carbohydrates, accumulation of calcium ions, formation of the Golgi complex
Mitochondria	there is	there is	Synthesis of ATP, native enzymes and proteins
Plastids	there is	no	Participation in photosynthesis, accumulation of starch, lipids, proteins, carotenoids
Ribosomes	there is	there is	Collection of the polypeptide chain (protein synthesis)
Microtubules and microfilaments	there is	there is	Allow the cell to retain a certain shape, are an integral part of the cell center, cilia and flagella, provide movement of organelles
Lysosomes	there is	there is	The digestion of substances within the cell, the destruction of its unnecessary structures, participation in the reorganization of cells, determine autolysis
Large central vacuole	there is	no	Provides the tension of the cell membrane, accumulates nutrients and cell life products, phytoncides and phytohormones, as well as pigments, is a reservoir of water
Golgi complex	there is	there is	Secrete and accumulate proteins, lipids and carbohydrates, modify the nutrients that enter the cell, is responsible for the formation of lysosomes
Cell center	There are, except for higher plants	there is	Is the center of the organization of the cytoskeleton, ensures a uniform divergence of chromosomes in cell division
Myofibrils	no	there is	Provide a reduction in muscle tissue

If we draw conclusions, then we can say that there are insignificant differences between the animal and plant cells. In this case, the functional features and structure of organoids (the table above, confirms this) has a general principle of organization. The cell functions as a coherent and integrated system. In this case, the functions of organoids are interrelated and are aimed at optimal work and maintenance of cell vital activity.