cell - is the level of organization of living matter, the independent biological system which has the basic characteristics of all living things.For example, it can develop, multiply, move, adapt and change.In addition, any inherent cells metabolism, specific structure, an ordered structure and functions.
science that deals with the study of cells - is cytology.Its subject is a structural unit of multicellular animals and plants, single-celled organisms - bacteria, protozoa and algae, consisting of a single cell.
If we talk about the overall organization of the structural units of living organisms, they consist of a membrane and the nucleus with the nucleolus.Also, they include cell organelles, the cytoplasm.Today, a variety of highly developed research methods, but takes the leading place microscopy, which allows one to study the structure of cells and investigate its basic structural elements.
What organelle?
organelles (also called organelles) - permanent constituent elements of any cells that make it a complete and perform certain functions.This structure, which is vital to sustain its activities.
By organelles include the nucleus, lysosomes, endoplasmic reticulum and Golgi complex, vacuoles and vesicles, mitochondria, ribosomes, and cell center (the centrosome).It also includes structures that form the cytoskeleton (microfilaments and microtubules), the melanosomes.We should also highlight the organelle movement.This is cilia, flagella, myofibrils and pseudopodia.
All these structures are interconnected and provide a coordinated activity of cells.That is why the question "What is the organelle?" - Can be answered, it is a component that can be equated to the body of a multicellular organism.
Classification organelles
Cells differ in size and shape, as well as their functions, but they are similar in chemical structure and the principle of a single organization.The question of what is and what is the organelle structure, quite debatable.For example, vacuoles, lysosomes, or sometimes referred to as cell organelles.
If we talk about the classification of the data components of the cells that secrete nemembrannye and membrane organelles.Nemembrannye - a cell center and the ribosome.Organelle movement (microtubules and microfilaments) are also deprived of the membranes.
The basis of the structure of membrane organelles is the presence of a biological membrane.Odnomebrannye dvumembrannye organelles and are coated with a uniform structure, which consists of a double layer of phospholipids and protein molecules.It separates the cytoplasm from the environment and helps to maintain the shape of the cell.It is worth remembering that in addition to the membrane of plant cells still have the shell and the outer cellulose, which is called a cell wall.It performs a supporting function.
to membrane organelles include EPS, lysosomes and mitochondria and plastids and lysosomes.These membranes may differ only by a set of proteins.
If we talk about the functional ability of organelles, some of them are able to synthesize certain substances.Thus, synthesis of important organelles - mitochondria, which produce ATP.Ribosomes, plastids (chloroplasts) and rough endoplasmic reticulum responsible for protein synthesis, smooth EPS - for the synthesis of lipids and carbohydrates.
consider the structure and function of organelles in more detail.
kernel
This organelle is extremely important, because when it is removed cells stop functioning and die.
nucleus has a double membrane, which has a plurality of pores.With them it is closely associated with the endoplasmic reticulum and cytoplasm.This organelle comprises chromatin - chromosomes that are complexes of proteins and DNA.With this in mind, we can say that it is the nucleus organelle that is responsible for maintaining the basic amount of the genome.
liquid portion of the kernel called karyoplasm.It contains the waste products of nuclear structure.The densest area - nucleolus, which houses the ribosome complex proteins and RNA, and phosphates of potassium, magnesium, zinc, iron and calcium.The nucleolus disappears before dividing cells and is formed again in the latter stages of the process.
endoplasmic reticulum (reticulum)
EPS - odnomembranny organelle.It occupies half the volume of the cells and consists of tubules and cisterns, which are interconnected, as well as the cytoplasmic membrane and the outer shell of the nucleus.The membrane of this organelle has the same structure as the plazmalema.This structure is integral and not open to the cytoplasm.
is smooth endoplasmic reticulum and granular (roughened).The inner shell of the granular EPS placed ribosome where protein synthesis takes place.On the surface of the smooth endoplasmic reticulum ribosomes are absent, but here goes the synthesis of carbohydrates and fats.
All substances that are formed in the endoplasmic reticulum, are carried on the system of tubules and ducts to destinations where they can accumulate and then used in a variety of biochemical processes.
Given the ability of synthesizing EPS rough reticulum placed in the cells, whose main function - the formation of proteins, and smooth - in the cells synthesizing carbohydrates and fats.In addition, the smooth reticulum accumulate calcium ions, which are necessary for normal functioning of cells, or whole organism.
It should also be noted that EPS is the place of formation of the Golgi apparatus.
lysosomes their functions
lysosomes - are cellular organelles that are presented odnomembrannymi pouches with a rounded shape and hydrolytic digestive enzymes (proteases, lipases and nucleases).For content characteristic acidic environment of lysosomes.Membranes data structures insulate them from the cytoplasm, preventing the destruction of the other structural components of cells.With the release of lysosomal enzymes into the cytoplasm of the cell self-destruction occurs - autolysis.
should be noted that the primary enzyme synthesized on the rough endoplasmic grid then moves to the Golgi apparatus.Here they are modified, packaged in membrane vesicles and begin to separate and become independent cell components - lysosomes, which are primary and secondary.
Primary lysosomes - structures that are separated from the Golgi apparatus, and the secondary (digestive vacuoles) - are those that are formed as a result of the merger of primary lysosomes and endocytic vacuoles.
Given this structure and organization, you can select basic function of lysosomes:
- digestion of different substances inside the cell;
- destruction of cellular structures that are not needed;
- participate in the reorganization process of cells.
vacuoles
vacuoles - organelles odnomembrannye is spherical shape, which is a reservoir of water and dissolved organic and inorganic compounds.In the formation of these structures involved Golgi apparatus and EPS.
in animal cell vacuoles bit.They are small and occupy no more than 5% by volume.Their primary role - providing transport substances across the cell.
plant cell vacuoles are large and take up 90% of the volume.In a mature cell has only one vacuole, which occupies a central position.Tonoplast membrane it is called, and the contents - cell sap.The main functions of the plant vacuoles - providing the voltage of the cell membrane, the accumulation of various compounds and cell wastes.Furthermore, these plant cell organelles supply water necessary for the photosynthesis process.
If we talk about the composition of the cell sap, that it includes the following substances:
- replacement - organic acids, carbohydrates and proteins, individual amino acids;
- compounds which are formed during the life of the cells and accumulated therein (alkaloids, phenols and tannins);
- volatile and plant hormones;
- pigments, due to which the fruits, roots and flower petals are painted in the appropriate color.
Golgi complex structure of organelles called "Golgi apparatus" is quite simple.In plant cells, they appear as separate calf membrane in animal cells, they are presented with tanks, canals and bubbles.Structural unit Golgi apparatus - is dictyosome which shows a stack of 4-6 "tank" and the small bubbles that are separated from and are intracellular transport system and can also serve as a source of lysosomes.Dictyosomes number can range from one to several hundred.
Golgi complex, usually located near the nucleus.In animal cells - near the center of the cell.The main functions of these organelles is the following:
- secretion and accumulation of proteins, lipids and sugars;
- modification organic compounds entering the Golgi complex;
- this organelle is the site of the formation of lysosomes.
should be noted that CSE lysosome, the vacuole, golgi apparatus and together form a tubular vacuolar-system which separates the cell into separate sections with corresponding functions.In addition, the system provides a continuous update of the membranes.
mitochondria - the energy plant cells
mitochondria - organelles dvumembrannye rod-shaped, spherical or filamentous form that synthesize ATP.They have a smooth outer surface and an inner membrane with numerous folds, called cristae.It should be noted that the number of cristae of the mitochondria may vary depending on the needs of the cells for energy.It focused on the inner membrane of many enzyme complexes that synthesize adenosine triphosphate.Here the energy of chemical bonds is converted into energy-rich bonds of ATP.Furthermore, cleavage takes place in the mitochondria of fatty acids and carbohydrates to release energy, which is stored and used in the processes of growth and synthesis.
internal environment data organelle called the matrix.It comprises a ring of DNA and RNA, small ribosome.Interestingly, the mitochondria - the semi-autonomous organelles, because they depend on the functioning of the cells, but at the same time, can maintain a certain independence.Thus, they are able to synthesize their own proteins and enzymes, as well as to reproduce themselves.
believed that mitochondria originated when released into the host cell aerobic prokaryotic organisms, which led to the formation of a specific complex symbiotic.Thus, mitochondrial DNA has the same structure as the DNA of modern bacteria and protein synthesis in mitochondria and bacteria is inhibited by the same antibiotics.
plastids - plant cell organelles
plastids are large enough organelles.They are present in plant cells only and are formed from precursors - proplastids contain DNA.These organelles play an important role in the metabolism and are separated from the cytoplasm by a double membrane.In addition, they may form an ordered system of internal membranes.
plastids are of three types:
- chloroplasts - the most numerous plastids are responsible for photosynthesis, which are formed when organic compounds and a free oxygen.These structures have a complicated structure and capable of moving in the cytoplasm toward the light source.The basic substance is contained in chloroplasts - chlorophyll, with which plants can use solar energy.It should be noted that the chloroplasts are similar to mitochondria are semi-autonomous structures, as capable of self-division and the synthesis of its own proteins.
- leucoplasts - colorless plastids, which, under the action of light transformed into chloroplasts.These cell components include enzymes.With them, glucose is converted and stored in the form of starch granules.In some plants, these plastids can accumulate lipids or proteins in the form of crystals and amorphous bodies.The largest number of leucoplasts concentrated in underground cells of plants.
- chromoplasts - derivatives other two types of plastids.The carotenoids are produced (with chlorophyll destruction), which are red, yellow or orange.Chromoplasts - the final stage of the transformation of plastids.Most of the fruit, petals and autumn leaves.
Ribosomes
What organelle called the ribosome?Organelles called ribosomes nemembrannye consisting of two fragments (small and large subunit).Their diameter is about 20 nm.They are found in all cell types.It organelles of animal and plant cells, bacteria.These structures in the nucleus and then transferred into the cytoplasm where placed loose or attached to the EPS.Depending on the properties of the ribosome synthesizing function alone or combined into complexes, forming polyribosomes.In this case, these organelles nemembrannye bind messenger RNA molecule.
ribosome contains 4 molecules of p-RNAs, which constitute its framework as well as various proteins.The main objective of this organelle - collecting the polypeptide chain, which is the first stage of protein synthesis.Those proteins that are produced by ribosomes of the endoplasmic reticulum, can be used throughout the body.Protein needs for individual cell are synthesized by ribosomes, which are located in the cytoplasm.It should be noted that the ribosomes are also found in mitochondria and plastids.
cytoskeleton
cell cytoskeleton formed microtubules and microfilaments.Microtubules are cylindrical formation 24 nm in diameter.Their length is 100 mm-1 mm.The main components - a protein called tubulin.He is unable to contract and can collapse under the influence of colchicine.Microtubules are in hyaloplasm and perform the following functions:
- create flexible, but at the same time, strong skeleton cells, which allows it to retain its shape;
- participate in the distribution of the chromosomes of the cell;
- provide moving organelles;
- contained in the cell center, as well as flagella and cilia.
microfilaments - threads that are placed under the plasma membrane and are composed of the protein actin and myosin.They can contract, resulting in movement of the cytoplasm is or protrusion of the cell membrane.Moreover, these components are involved in the formation of the waist during cell division.
Cellular Center (centrosome)
This organelle is composed of two centrioles and tsentrosfery.Centrioles cylindrical shape.Its walls are formed by three microtubules, which merge with each other through cross-linking.The centrioles are arranged in pairs at right angles to each other.It should be noted that the cells of higher plants are deprived data organelles.
The main role of the center of the cell - to ensure even distribution of chromosomes during cell division.He also is the center of the organization of the cytoskeleton.
organelles movement
By organelles include movement of cilia and flagella.This tiny growths of hair.The flagellum contains microtubule 20.His foundation is located in the cytoplasm and is called the basal body.Flagellum length is 100 m or more.Flagella, which are only 10-20 microns are called cilia.When sliding microtubules of cilia and flagella are able to fluctuate, causing the movement of the cell.The cytoplasm can contain contractile fibrils, which are called myofibrils - is an animal cell organelles.Myofibrils usually placed in myocytes - muscle cells as well as cells of the heart.They consist of smaller fibers (protofibrils).
Note that bunches of myofibrils composed of dark fiber - is anisotropic discs, as well as light areas - it is isotropic disks.The structural unit of myofibrils - sarcomere.This is the area between the anisotropic and isotropic disk, which has the actin and myosin filaments.
