Among the variety of organisms currently existing on Earth, two groups are distinguished: viruses and phages that do not have cellular structure; all other organisms are diverse cellular forms life. There are two types of cellular organization: prokaryotic and eukaryotic.
Most modern living organisms belong to one of the three kingdoms - plants, fungi and animals, united in the supra-kingdom of eukaryotes.
They are on the same level as bacteria. They are prokaryotic, autotrophic organisms with non-membrane organelles that contain chlorophyll, phycocyanin, and other dyes used in photosynthesis. They live in water and damp places. This was probably the first source of O2 in the Earth's atmosphere.
A cell is the smallest functional structure of any living organism. The organelle is found in the cells of animals, plants and fungi, suspended in the gelatinous cytoplasm. The organelle is typical of eukaryotic cells. In the cells of simple unicellular organisms there are no complex organelles. These cells are called prokaryotic cells.
For vegetable cells are characterized by the presence of a thick cellulose cell wall, various plastids, large central vacuole, shifting the core to the periphery. Cell Center higher plants does not contain centrioles. Plant cells store starch as a reserve nutrient carbohydrate.
In cages mushrooms the cell wall contains chitin, there is a central vacuole in the cytoplasm, and there are no plastids. Only some fungi have a centriole in the cell center. The main reserve polysaccharide is glycogen.
The organelle may be of plasma or non-plasma origin. Nonplastic organelles include vacuoles and cell walls. Plasma organs include: cytoplasm, cell membrane, nucleus, Golgi apparatus, endoplasmic reticulum, plastics, mitochondria, ribosomes, lysosomes Lysosomes Organosalt cells, spherical, surrounded by one cytoplasmic membrane. More Biological Dictionary and Microtube.
All of these structures are present in eukaryotic cells. Prokaryotic cells do not possess them and are characterized by a simple structure in which the genetic material occurs as a tangled strand of nucleic acid. The cell, as an independent structure, must be somehow separated from the environment. For this purpose, a cell membrane or plasma is used. They are the site of synthesis and accumulation of fat reserves.
Animals cells have, as a rule, a thin cell wall, do not contain plastids and a central vacuole; a centriole is characteristic of the cell center. The storage carbohydrate is glycogen.
Depending on the number of cells that make up organisms, the latter are divided into unicellular and multicellular. Unicellular organisms consist of a single cell that performs the functions of a complete organism. Many of these cells are much more complex than the cells of a multicellular organism.
Cytoplasmic membranes are composed of a lipid bilayer, which is based on phospholipids. Proteins, whose content in the membrane can vary from 25% to 75%, are also included in this layer. These proteins may be immersed or may protrude above the membrane surface. The plasmalemma may also contain a small amount of sugar.
The cell membrane is designed to separate the cell body from external environment and maintain its shape. Membranes are involved in the transport of various substances between the environment and inside cells. Due to the hydrophobicity of the membrane, the transport element of the transport of the national economy is called communication. Movement of goods and people. Animals in many parts of the world are the main means of transportation. More Glossary is usually done using appropriate protein carriers.
Body multicellular organisms consists of many cells combined into tissues, organs and organ systems. The cells of a multicellular organism are specialized to perform a certain function and can exist outside the body only in a microenvironment close to physiological (for example, under tissue culture conditions). Cells in a multicellular organism vary in size, shape, structure, and function. Despite individual characteristics, all cells are built according to a single plan and have many common features.
They are protective barrier cells. Hormones are biologically active substances, carrying specific information obtained by both plants and animals. More Biological vocabulary associated with the corresponding receptors located in the membrane. The cell membrane is semi-liquid, its individual components can move within it.
This is especially important when transporting substances through membranes. It is the most important cellular organelle as it contains the genetic information carriers i.e. genes. The nucleus ranges in size from about 0.5 to 600 nm and is most often spherical, although lenticular and rodent nuclei are present. As a rule, one cell contains one core. Fungi are non-parasitic, including parasites, saprophytes, and symbionts. Fungal cells sometimes have two nuclei lying next to each other, called conjugated nuclei.
The basis of the structural organization of the cell is biological membranes, which is based on plasma membrane, or plasmalemma, having a typical structure and thickness of 7.5 nm. Membranes are made up of proteins and lipids. Lipids (mainly phospholipids) form a liquid bimolecular layer, in which the hydrophobic tails of the molecules are turned inside the membrane, and the hydrophilic tails are turned towards its surfaces. Protein molecules are able to move in lipid layers, being located either on the outer or inner surface membrane, or penetrating it through. Penetrating proteins, gathering in a circle, form a pore through which some compounds can pass from one side to the other. The membranes also contain carbohydrates in the form of glycolipids and glycoproteins located on the outer surface of the membrane. The set of proteins and carbohydrates on the surface of the membrane of each cell is specific and determines its "passport" data. Membranes have the property of selective permeability (they are able to pass some substances and not pass or pass others worse), as well as the property of spontaneous restoration of the integrity of the structure. The carbohydrate component in the composition of the cell membranes of different cells is expressed to varying degrees. In animal cells, it is relatively thin and is represented by oligosaccharide groups of glycoproteins and glycolipids of the membrane and is called the glycocalyx. In plant cells, the carbohydrate component of the cell membrane is strongly expressed and is represented by a cellulose cell wall.
The nucleus is surrounded by a double cytoplasmic membrane called nuclear envelope. There is a narrow space between the membranes, in some places these membranes are connected and form holes - the nuclear pore. Thanks to these pores, it is possible to transfer some molecules from the nucleus to the cytoplasm and vice versa. Outer shell the nuclear envelope is directly connected to the mesoparticle located near the nucleus. Specific layered proteins adhere to the inner layer that forms the backbone of the nuclear envelope. These whites are extremely important in reproducing this cell cell after cell division.
Cell wall performs important and very diverse functions:
Determines and maintains the shape of the cell;
Protects the cell from mechanical influences and penetration of foreign bodies;
Carries out the reception (recognition) of many molecular signals (for example, hormones);
Delimits the internal contents of the cell;
Chromosomes are a condensed form of chromatin. On the other hand, there is also a free form - in the form of slightly twisted threads. Chromosomes contain genes, which means important genetic information. During cell division, it is important that this information reaches both progeny cells. In order for the chromosomes in the daughter cells to match the number of chromosomes present in the parent cell, they must be multiplied before dividing. After each chromosome, the chromosome subdivides into a form of genetic material.
Entry of the virus into the host
Chromosomes become visible under a light microscope during karyokinesis, when the chromatin experiences helix. More Biological Dictionary has its own copies, with which the so-called. telomere. During cell preparation, chromatin condenses into short, thick chromosomes with a highly packed structure. Chromosomes in this form can be observed under a microscope.
Regulates the metabolism between the cell and the environment, ensuring the constancy of the intracellular composition;
Participates in the formation of intercellular contacts and various kinds specific protrusions of the cytoplasm (microvilli, cilia, flagella).
The exchange of substances between the cell and its environment occurs constantly. The mechanism of transport of substances into and out of the cell depends on the size of the transported particles. Small molecules and ions are transported by the cell directly across the membrane in the form of passive and active transport.
The largest structure in the nucleus is the nucleus, which synthesizes ribosomes. The nucleus is not surrounded by a cytoplasmic membrane or has complex structure. It contains special enzymes of enzymatic biocatalysts, increasing the rate of biochemical reactions through the specific activation of substrates. Read more Biological vocabulary needed to create ribosomes.
Ribosomes are the structures on which the biosynthesis of biosynthesis occurs, the synthesis chemical compounds in living cells. It is characterized high speed, it depends on the activity of the corresponding enzymes. More Biological Dictionary. Nai more occurs in the rough endoplasmic reticulum, but also in the cytoplasm. They are spherical and consist of two subunits different size. The proteins required for the synthesis of ribosomes come from the cytoplasm to the nucleus and into the nucleus. Ribosomal subunits are formed in the nucleus.
^ Passive transport carried out without energy expenditure, by simple diffusion, osmosis or facilitated diffusion with the help of carrier proteins.
active transport- with the help of carrier proteins and requires energy expenditure. The transfer of macromolecules and larger particles occurs due to the formation of bubbles surrounded by a membrane. Depending on the type and direction of transport, there are endocytosis and exocytosis. The absorption and release of solid and large particles are respectively named phagocytosis and reverse phagocytosis, liquid or dissolved particles pinocytosis and reverse pinocytosis.
Basic forms of eukaryotic cells
When the subunits come together, the normal chromosomes leave the nucleus through the nuclear pores and enter the cytoplasm. More The biological dictionary is involved in protein production. The nucleus is of paramount importance to other organelles, since it contains all the information for the construction of the entire organism. The nucleus is involved in cell division and thus transmits this information to the daughter cell. The nucleus is also the site of synthesis of ribosomal subunits.
The mesentery, otherwise known as the endoplasmic reticulum, is a complex membrane system that creates cisterns, tubules and vesicles that are involved in the transport of various substances within the cell. These membranes divide the cell into different compartments so that different reactions can occur at the same time. The interior of all these baths and cisterns forms a specific cell compartment.
The cytoplasm is the internal contents of the cell and consists of the main substance, or hyaloplasm, and various organelles located in it.
^ Hyaloplasm (matrix) - This aqueous solution inorganic and organic matter, capable of changing its viscosity and being in in constant motion. The ability to move, or the flow of hyaloplasm, is called cyclosis. In the process of cyclosis, the movement of substances and structures located in the cytoplasm occurs. The matrix is an active medium in which many chemical and physiological processes and which unites all the components of the cell into single system. During the life of the cell in the cytoplasm are deposited various substances, forming non-permanent structures - inclusions (clumps of glycogen, fat drops, pigment granules).
The mesenchymal blade is rich in a system of many enzymes that are necessary in cellular metabolism, influencing many biochemical reactions. Outer side The cytoplasmic reticulum is covered with a large number of spherical ribosome particles. The inner side facing the light of the mesh does not contain ribosomes and is called a smooth mesh.
Ribosomes placed on a membrane are specific machines for protein production. Production Organized activity human, consisting in the production of material goods and the provision of services to meet needs. More Geographic dictionary of proteins is found not only in the membranes of rough tissue, some proteins are formed on free cytoplasmic ribosomes not associated with the membrane.
All cell organelles are divided into membrane And non-membrane. Among membrane organelles exist single membrane(endoplasmic reticulum, Golgi complex, lysosomes) and d double membrane(mitochondria, plastids).
^ Endoplasmic reticulum (ER, reticulum). This organoid was discovered by the American scientist Keith Roberts Porter in 1945. The totality of vacuoles, channels, tubules forms a membrane network inside the cytoplasm, combined into a single whole with outer membrane nuclear shell. There are two types of endoplasmic reticulum membranes - rough (granular)) And smooth (agranular).
In the endoplasmic reticulum, the resulting proteins undergo post-transcriptional treatment. This process consists of folding proteins, forming their respective spatial structure, and incorporating sugars or lipid moieties. Proteins produced on the membrane pass into its light and undergo various processes transformations. They are then transported to network bubbles, which, once disconnected from this system, transport them to their destination. The transfer of the follicular protein to said organelle fuses seamlessly with the follicular membrane.
Ribosomes are located on the surface of the rough ER membranes, which synthesize all the proteins that make up the ER membrane, as well as the proteins necessary for the life of the cell. The synthesized protein molecules enter the EPS channels. There they are modified, and then transferred through the system of channels to the part of the cell where they are needed. Accumulations of a rough endoplasmic reticulum are characteristic of cells actively synthesizing secretory proteins. For example, in liver cells, nerve cells, in cells of the pancreas.
Metabolic reactions occur in the smooth zone of the reticulum fatty acids, steroids and phospholipids. There are also processes for detoxification of carcinogens. Liver cells have these detoxifying properties because they contain a relatively large smooth mesh compared to other cells.
The Golgi apparatus was discovered by the Italian researcher Camillo Golgi, thanks to its specific staining of microscopic specimens. The Golgi apparatus consists of fairly large, flat cisterns that stick to each other. At the point of adhesion, these tanks are rather narrow, and in the extreme parts they often expand due to the accumulation cell products. Each flattened bag has a light, that is, an interior space. However, all these Golgi apparatuses are not interconnected, and their internal spaces do not have continuity, as in the endoplasmic reticulum.
Unlike the granular endoplasmic reticulum, there is no smooth network of ribosomes on the membranes. This network is involved in the synthesis of lipids and carbohydrates, and neutralizes toxic (poisonous) substances. So, with some poisonings, extensive zones appear in the liver cells, filled with smooth EPS membranes. Thus, EPS serves as a "factory" for production of membrane and transportable proteins and lipids, and also implements a system of their transport within the cell.
In animal cells, there is only one Golgi apparatus, which is usually located near the nucleus. However, in most plant cells and some animals, the Golgi body is present in more common, differentiated cells. The Golgi apparatus is primarily designed to modify and sort proteins. Almost every protein molecule produced in a cell is modified in the Golgi apparatus. The Golgi Glaucoma proteins undergo many changes, often changing their chemical properties.
Each protein is individually transformed. Lysosomes are present only in animal cells. These are small vesicles surrounded by a single plasma membrane. Inside them there is a honeycomb juice containing a lot digestive enzymes. These enzymes show optimal performance in pH environments. Lysosomal enzymes are included in many groups. to hydrolases, amylases, peptidases and others. In total, lysosomal juice contains about 40 different enzymes that break down proteins, fats, carbohydrates, and nucleic acids.
^ Golgi complex (Golgi apparatus). Discovered in 1898 by the Italian scientist Camillo Golgi, while studying the structure of nerve cells. It consists of 5-20 flattened disk-shaped membrane cavities, as if collected in a stack, and microbubbles laced from them. The Golgi complex plays the role of a kind of center where the final sorting and packaging various products cell activity and transport them according to their destination: to various intracellular structures or outside the cell by exocytosis. The membranes of the Golgi apparatus are also capable of synthesize polysaccharides And form lysosomes.
Digestive enzymes synthesized in the cell are delivered to lysosomes using special signaling molecules. The cell membrane surrounding the lysosome protects the cell from the release of enzymes that can digest cellular components. IN critical situations When a cell has specific energy requirements from lysosomes, enzymes that release cell organelles are released to provide the required energy.
They are attributed to the kingdom of Monera. Read the biological dictionary or the remains of dead cells. These lysosomes are responsible for tail resorption during the transformation of the tadpole into an adult. It is likely that the joint disease is also caused by excessive activity of lysosomes in the tissues of the goddess. The lysosomes of these tissues release enzymes that break down cartilage tissue.
Lysosomes perform a function intracellular digestion of macromolecules food and foreign components entering the cell during phago- and pinocytosis, providing the cell with additional raw materials for chemical and energy processes. During starvation, lysosome cells digest some organelles and replenish the supply of nutrients for a while. In the process of development in animals, the death of individual cells and even organs (metamorphosis) often occurs, which is carried out with the indispensable participation of lysosomes. To carry out these functions, lysosomes contain about 40 enzymes that destroy proteins, nucleic acids, lipids, carbohydrates, etc.
Distinguish primary and secondary lysosomes. Primary lysosomes are microvesicles that detach from the cavities of the Golgi apparatus, surrounded by a single membrane and containing a set of enzymes. After the fusion of primary lysosomes with some substrate to be cleaved, various secondary lysosomes are formed. An example of secondary lysosomes is the digestive vacuoles of protozoa. If the contents of the lysosome are released inside the cell itself, then self-destruction of the cell occurs - autolysis.
In eukaryotic cells, there are also organelles isolated from the cytoplasm by two membranes. These organelles are mitochondria and plastids. According to the symbiotic hypothesis about the origin of the eukaryotic cell, they are the descendants of ancient prokaryotic symbiont cells: bacteria and blue-green algae. These organelles are called semi-autonomous, since they have their own apparatus for protein biosynthesis (circular DNA, ribosomes, tRNA, enzymes) and synthesize some of the proteins that function in them.
Mitochondria found in almost all aerobic eukaryotic cells, with the exception of mature mammalian erythrocytes. Their number in different cells is different and depends on the level of functional activity of the cell. Mitochondria are highly variable in size and shape (rod-shaped, round, oval). Outside, mitochondria are limited by a smooth outer membrane, similar in composition to the plasma membrane. The inner membrane forms numerous outgrowths (cristae) and contains numerous enzymes involved in energy conversion processes. nutrients V ATP energy. It also occurs in mitochondria synthesis steroid hormones . Mitochondria have their own ribosomes and DNA, so they are able to synthesize proteins. In living cells, mitochondria can move, merge with each other, and divide. Their number in a cell varies greatly - from units to tens of thousands, usually there are more mitochondria in those parts of the cytoplasm and in those cells where there is an increased need for energy. Especially rich in mitochondria muscle tissues and cells of the nervous tissue.
Plastids are organelles characteristic only for cells of photosynthetic eukaryotic organisms. Depending on the color, three main types are distinguished: chloroplasts, chromoplasts and leucoplasts.
Chloroplasts- relatively large oval or disc-shaped cell structures. The content of plastids is called stroma. The outer membrane is smooth, the inner one forms lamellar invaginations - thylakoids, most of which is stacked in the form of a stack of coins and forms grains. The arrangement of the grains in a checkerboard pattern ensures maximum illumination of each grain. Gran membranes contain chlorophyll, which gives the chloroplast its green color and light phase of photosynthesis.
Thylakoid-forming membranes contain pigments that trap sunlight, and enzymes that synthesize ATP. The chloroplast matrix contains enzymes that synthesize organic compounds and using the energy of ATP. Chloroplasts contain their own DNA and ribosomes. They are capable of autonomous reproduction, independent of cell division. In autumn, chloroplasts turn into chromoplasts - plastids with yellow, red and orange color.
Chromoplasts they are simpler, they do not have grains, they are not capable of photosynthesis, they contain a variety of pigments: yellow, orange and red carotenes and xanthophylls. They give a bright color flowers and fruits, attracting animals and thus facilitating the pollination of plants and the dispersal of seeds.
Leucoplasts almost devoid of thylakoids, the pigments in them are in an inactive form (protochlorophylls). Leucoplasts are colorless, contained in the cells of underground or uncolored parts of plants (root, rhizome, tubers). Able accumulate spare nutrients, primarily starch, lipids and proteins. In the light they can turn into chloroplasts (greening of potato tubers).
Ribosomes. Submicroscopic non-membrane organelles, the function of which is - protein synthesis, due to which they are obligatory organelles in the cells of all living organisms. Each ribosome in working condition consists of two subunits - large and small, which include protein molecules and ribosomal RNA. Ribosomal RNA is synthesized in the nucleus on the DNA molecule of one or more chromosomes in the nucleolus zone. Ribosomes are also formed there, which then leave the nucleus. In the cytoplasm, ribosomes can be in a free state or located on rough ER membranes. Depending on the type of protein being synthesized, ribosomes can “work” singly or combine into complexes - polyribosomes. In such complexes, ribosomes are linked by a single mRNA molecule.
^ Cell center. A non-membrane organelle present in the cells of animals, fungi and lower plants. Consists of two centrioles located perpendicular to each other. Each centriole has the form of a hollow cylinder, the wall of which is formed by 9 triplets of microtubules. In the process of cell division, centrioles double, diverge towards the poles and form a division spindle, ensuring the distribution of chromosomes between daughter cells.
cytoskeleton It is formed by microtubules and microfilaments - filamentous structures consisting of various contractile proteins and causing the motor functions of the cell. Microtubules look like long hollow cylinders, the walls of which are composed of proteins - tubulins. Microfilaments are very thin, long, filamentous structures composed of actin and myosin.
Microtubules and microfilaments lower the entire cytoplasm of the cell, form its cytoskeleton, causing intracellular movement of organelles, changing cell shape And the position of its organelles.
Vacuole- an essential part of the plant cell. This is a large membrane vesicle filled with cell sap, the composition of which differs from the surrounding cytoplasm. Vacuole accumulates reserve nutrients and regulates water-salt metabolism, controlling flow of water into and out of the cell.
^ Cell inclusions. In addition to membrane and non-membrane organelles in cells, there can be cellular inclusions, which are non-permanent formations, either arising or disappearing in the process of cell life.
By nature, all inclusions are products cell metabolism. They accumulate mainly in the form of granules, droplets and crystals. Chemical composition inclusions are very diverse - lipoids, polysaccharides (glycogen, starch), proteins, some pigments, etc.
The nucleus is an essential component of all eukaryotic cells. ^ Cell nucleus stores hereditary information and controls the processes of intracellular metabolism, ensuring the normal functioning of the cell and the performance of its functions. As a rule, the nucleus has a spherical shape, there are also spindle-shaped, horseshoe-shaped, segmented nuclei. Most cells have one nucleus, but, for example, ciliates have two nuclei - macronucleus and micronucleus, and in striated muscle fibers there are hundreds of nuclei. The nucleus and cytoplasm are interconnected components of the cell that cannot exist without each other. Their constant interaction ensures the unity of the cell both structurally and functionally. In eukaryotic organisms, there are cells that do not have nuclei, but their lifespan is short. In the process of maturation, erythrocytes lose their nucleus, which function for no more than 120 days, and then are destroyed in the spleen. Non-nucleated platelets circulate in the blood for about 7 days. There is no nucleus in the cells of sieve tubes in angiosperms.
Each cell nucleus is surrounded nuclear membrane, contains nuclear juice (karyoplasm, nucleoplasm), chromatin and one or more nucleoli.
^ nuclear envelope . This shell separates the contents of the nucleus from the cytoplasm of the cell and consists of two membranes having a typical structure for all membranes. The outer membrane passes directly into the endoplasmic reticulum, forming a single membrane structure of the cell. The surface of the nucleus is permeated with pores through which exchange various materials between nucleus and cytoplasm. For example, RNA and ribosome subunits exit the nucleus into the cytoplasm, and the nucleotides necessary for the assembly of RNA, enzymes and other substances that ensure the activity of nuclear structures enter the nucleus.
^ Nuclear sap (karyoplasm, nucleoplasm) is a jelly-like solution that contains a variety of proteins, carbohydrates, nucleotides, ions, as well as chromosomes and the nucleolus.
nucleolus- a small rounded body, intensely stained and found in the nuclei of non-dividing cells. Function of the nucleolus synthesis of rRNA and their connection with proteins, i.e. assembly of ribosome subunits.
Chromatin - lumps, granules and filamentous structures that are specifically stained by some dyes, formed by DNA molecules in combination with proteins - histones. It is the histones that provide the structure and packaging of DNA. different plots DNA molecules in chromatin have varying degrees spiralization, and therefore differ in color intensity and the nature of genetic activity. Chromatin is a form of existence of genetic material in non-dividing cells and provides the possibility of doubling and realizing the information contained in it. In the process of cell division, DNA spiralization occurs, and chromatin structures form chromosomes. In fact, chemically, chromatin and chromosomes are one and the same.
Chromosomes- dense, intensely staining structures, which are units of the morphological organization of the genetic material and ensure its precise distribution during cell division. Chromosomes are best seen at the metaphase stage of mitosis. Each metaphase chromosome consists of two chromatids.
Chromatids- highly helical identical DNA molecules formed as a result of replication. Chromatids join together at the primary constriction, or centromeres. The centromere divides the chromosome into two arms. Chromosomes are classified according to the location of the centromere. equal-arm, unequal-arm and rod-shaped. Some chromosomes have secondary constrictions that separate satellites. Secondary constrictions of a number of chromosomes are involved in the formation of the nucleolus.
The number, size, and shape of chromosomes are unique to each species. ^ The totality of all signs of a chromosome set characteristic of a particular species, called karyotype. Our genetic data bank consists of 46 chromosomes of a certain size and shape, carrying more than 30,000 genes. These genes determine the structure of tens of thousands of proteins, various kinds RNA and proteins are enzymes that form fats, carbohydrates and other molecules. Any change in the structure or number of chromosomes leads to a change or loss of part of the information and, as a result, to a violation normal functioning the cell in which they are located.
In somatic cells, the number of chromosomes is usually twice as large as in mature germ cells. At fertilization, half of the chromosomes come from maternal organism and half of the paternal, i.e. in the nucleus of a somatic cell, the chromosomes are paired. Such paired, identical in shape and size of chromosomes, carrying the same genes, called homologous. The chromosome set, represented by paired chromosomes, is called double or diploid and denote 2n. The presence of a diploid chromosome set in most higher organisms increases the reliability of the functioning of the genetic apparatus. Each gene that determines the structure of a particular protein, and ultimately affects the formation of a particular trait, in such organisms is represented in the nucleus of each cell in the form of two copies - paternal and maternal.
During the formation of germ cells from each pair of homologous chromosomes, only one chromosome enters the egg or sperm cell, therefore the germ cells contain a single, or haploid, set of chromosomes (1n).
Chromosomes in the karyotype are also divided into autosomes, or non-sex chromosomes, the same in males and females, and heterochromosomes, or sex chromosomes involved in sex determination and differing in males and females.
There is no relationship between the number of chromosomes and the level of organization of a given species: primitive forms may have more chromosomes than highly organized ones, and vice versa. For example, in such distant species as the agile lizard and the fox, the number of chromosomes is the same and equal to 38, in humans and ash - 46 chromosomes each, in chicken 78, and in crayfish over 100!
The constancy of the number and structure of chromosomes in cells is necessary condition the existence of a species and individual organism. When studying the chromosome sets of different individuals, we found twin species, which morphologically do not differ at all from each other, but, having different number chromosomes or differences in their structure, did not interbreed and developed independently. Such, for example, are two species of Australian grasshoppers and black rats living in the same territory.
^ Diversity of prokaryotes . The kingdom of prokaryotes is mainly represented by bacteria, the most ancient organisms on our planet. Having emerged more than 3.5 billion years ago, prokaryotes actually created the Earth's biosphere, creating the conditions for the further evolution of organisms.
For the first time, bacteria were seen under a microscope and described in 1683 by the Dutch naturalist A. Leeuwenhoek. The sizes of bacteria range from 1 to 15 microns. A single bacterial cell can only be seen with a fairly sophisticated microscope, which is why they are called microorganisms.
Bacteria live everywhere: in the soil, in the air, on the surface and inside other organisms, in food products. Some bacteria settle in hot springs where the water temperature reaches 78ºС and higher. The number of bacteria on the planet is enormous, for example, 1 g of fertile soil contains about 2.5 billion bacterial cells.
The shape of bacteria is extremely diverse. Allocate rod-shaped - bacilli, spherical – cocci, spiral - spirilla, having the form of a comma - vibrios.
Many prokaryotes are capable of spore formation. Spores arise, as a rule, under unfavorable conditions and are cells with a sharply reduced level of metabolism. Spores are covered with a protective shell, remain viable for hundreds and even thousands of years and withstand temperature fluctuations from -243 to + 140ºС. On the onset favorable conditions spores "sprout" and give rise to a new bacterial cell.
Thus, sporulation of prokaryotes is a stage life cycle providing an experience adverse conditions environment. In addition, in the state of spores, microorganisms can be easily spread by wind and other means.
^ The structure of a prokaryotic cell . The cell is surrounded by a membrane of the usual structure, outside of which there is a cell wall, consisting of a special glycopeptide - murein. In the central part of the cytoplasm, there is one circular DNA molecule, not separated by a membrane from the rest of the cytoplasm. The area of a cell that contains genetic material is called nucleoid. In addition to the main circular "chromosome", bacteria usually contain several small DNA molecules in the form of small, loosely arranged rings, the so-called plasmid, involved in the exchange of genetic material between bacteria.
In a bacterial cell, there are no membrane organelles characteristic of eukaryotes (EPS, Golgi apparatus, mitochondria, plastids, lysosomes). The functions of these organelles are performed by invaginations cell membrane- mesosomes.
Ribosomes are essential organelles that provide protein synthesis in bacterial cells.
On top of the cell wall, many bacteria secrete mucus, forming a kind of capsule, additionally protecting the bacterium from external influences.
bacteria multiply simple division in two. After the reduplication of the circular DNA, the cell elongates and a transverse septum is formed in it. Subsequently, the daughter cells diverge or remain connected in groups.
Comparing prokaryotic and eukaryotic cells, it can be noted that the structure of two-membrane organoids - mitochondria and plastids, which have their own circular DNA and ribosomes that synthesize RNA and proteins - resembles the structure bacterial cell. This similarity formed the basis of the hypothesis of the symbiotic origin of eukaryotes. Several billion years ago, prokaryotic organisms were introduced into each other, resulting in a mutually beneficial union.
Prokaryotic organisms also include cyanobacteria, often referred to as blue-green algae. These ancient organisms, which originated about 3 billion years ago, are widely distributed throughout the world. About 2 thousand species of cyanobacteria are known. Most of them are able to synthesize everything necessary substances using light energy.
^ Credit
Question 13. Organismic level and population-species levels. Biocenotic and biospheric levels
1. Variety of forms
On organism level an unobservable variety of forms is found. The diversity of organisms belonging to different species, and even within the same species, is not a consequence of diversity, but of their increasingly complex spatial combinations, causing new qualitative features. There are currently over a million animal species and about half a million plant species on Earth. Each species consists of separate individuals (organisms, individuals), each of which has its own distinctive features.
2. Individual
An individual - an organism as a whole - elementary unit of life. Life does not exist outside of individuals in nature. At the organismic level, the processes of ontogeny proceed. The nervous and humoral systems carry out a certain homeostasis.
Set of organisms(individuals) of the same species inhabiting certain territory, is population. A population is an elementary unit of the evolutionary process; the processes of speciation originate in it. Populations are part of biogeocenoses.
3. Biogeocenoses
Biogeocenoses - historically established sustainable communities populations different types related to each other and to the environment inanimate nature exchange of substances, energy and information. They are elementary systems in which the material-energy cycle is carried out, due to the vital activity of organisms. Biogeocenoses make up the biosphere and determine all the processes occurring in it.
Only with a comprehensive study of the phenomena of life at all levels can one get a holistic view of a special biological form of the existence of matter.
4. Principles of Medicine
The idea of the levels of organization of life is directly related to the main principles of medicine. It makes one consider healthy or sick human body as an integral, but at the same time complex hierarchically subordinated system. The meaning of structures and functions at each of these levels helps to reveal the essence of the disease process. Accounting for the human population to which this individual belongs may be required, for example, in the diagnosis hereditary disease . To reveal the features of the course of the disease and the epidemic process, it is also necessary to take into account the features of the biocenotic and social environment. Whether the doctor is dealing with an individual patient or a human team, he is always based on a complex of knowledge gained at all levels of the biological micro-, meso- and macrosystems.
Question 14. Cell as a structural unit. Cell structure. General issues
1. Cell as elementary biological system
All living organisms are built from cells. Unicellular organisms (bacteria, protozoa, many algae and fungi) consist of one cell, multicellular organisms (most plants and animals) usually consist of many thousands of cells.
Cell – elementary biological system capable of self-renewal, self-reproduction and development. Cell structures underlie the structure of plants and animals. No matter how diverse the structure of organisms may seem, it is based on similar structures - cells. The cell has all properties of a living system: it exchanges matter and energy, grows, multiplies and inherits its characteristics, reacts to external signals (stimuli), is able to move. It is the lowest level of organization that has all these properties, the smallest structural and functional unit alive. It can also live separately - isolated cells of multicellular organisms continue to live and multiply in a nutrient medium. Functions in the cell are distributed among various organelles, such as the cell nucleus, mitochondria, etc.
2. cell diversity
In multicellular organisms different cells (e.g. nerve, muscle, blood cells) perform different functions("division of labor") and therefore differ in their structure. Despite this, the variety of forms and organization of cells are subject to uniform structural principles.
cell shape unusually diverse - from the simplest spherical ( unicellular organisms; among bacteria - cocci) to the most bizarre. Micrococci have a diameter of 0.2 microns, nerve cells reach a length of 1 m, and the lactiferous vessels of plants - even several meters.
3. cell structure
The living content of the cell, protoplasm, is separated from the environment by a plasma membrane (plasmolemma) and can be, in addition, surrounded by a strong cell wall. Protoplasm is a gelatinous heterogeneous mass with many different organelles and paraplasmic inclusions. The latter are only conventionally classified as living protoplasm and contain substances to be accumulated or excreted.
4 . Structural elements cells
Exist two levels of organization cells: a prokaryotic cell (in prokaryotes - bacteria and blue-green algae, most of them unicellular) and a eukaryotic cell (in eukaryotes, that is, all other unicellular and multicellular organisms - plants, fungi and animals).
Table 2. Structural elements of the cell
Question 15. Eukaryotic and prokaryotic cells
1. Characterization of eukaryotic cells
The average size of a eukaryotic cell is about 13 microns (but there are large variations in size). The cell is divided by internal membranes into different compartments (reaction spaces). Three types of organelles(layers) are clearly delimited from the rest of the protoplasm (cytoplasm) by a shell of two membranes: the cell nucleus, mitochondria and plastids (the latter only in plants). Plastids serve mainly for photosynthesis, and mitochondria for energy production. All layers contain DNA as a carrier of genetic information.
Cytoplasm contains various organelles for the most part visible only with an electron microscope, including ribosomes, which are also found in plastids and mitochondria. All organelles lie in the matrix (this is the part of the cytoplasm that even in electron microscope appears to be homogeneous).
2. Basic forms of eukaryotic cells
Exist three main forms eukaryotic cells: plant cells, fungal cells and animal cells.
Table 3. Main forms of eukaryotic cells
3. Characterization of prokaryotic cells
The average size of prokaryotic cells is 5 microns. They do not have any internal membranes other than protrusions of internal membranes and plasma membrane. The layers are missing. Instead of the cell nucleus, there is its equivalent (nucleoid), devoid of a shell and consisting of a single DNA molecule. In addition, bacteria can contain DNA in the form of tiny plasmids similar to eukaryotic extranuclear DNA.
IN prokaryotic cells capable of photosynthesis (blue-green algae, green and purple bacteria), there are variously structured large protrusions of the membrane - thylakoids, which in their function correspond to eukaryotic plastids. The same thylakoids or, in colorless cells, smaller protrusions of the membrane (and sometimes even the plasma membrane itself) functionally replace mitochondria. Other complexly differentiated protrusions of the membrane are called mesosomes; their function is unclear. Only some organelles prokaryotic cells are homologous to the corresponding eukaryotic organelles. Prokaryotes are characterized by the presence of a moray sac - a mechanically strong element of the cell wall.
Question 16
1. Characterization of viruses
Viruses are non-cellular formations- very small particles (virions), consisting of nucleic acid (DNA or RNA, single or double stranded, serving as genetic material) and a protein shell, sometimes containing lipids.
The shell (capsid) is built from subunits (capsomeres), which consist of one or more identical or different polypeptide chains.
Viruses species-specific and multiply only in living host cells. There are bacterial viruses (phages), plant viruses and animal viruses. Outside the host cell, virions do not metabolize and do not show any other signs of life.
2. Entry of the virus into the host
IN host cell the virion or only its nucleic acid penetrates. There this nucleic acid, using the replication system and the protein-synthesizing apparatus of the host cell, multiplies (replicates) and provides viral protein synthesis.
At virulent viruses the resulting virions are released gradually or all at once as a result of cell destruction. In temperate phages, the DNA can be inserted into the DNA of the host cell as a provirus and replicate along with it. The formation of virions occurs only with its induction various factors(irradiation, chemical agents, elevated temperature).
Viruses serve pathogens, because when they are released, they destroy the host cell or cause a violation of its metabolism.
Question 17. Cytoplasm. Ribosomes and plasmids
1. The composition of the cytoplasm
Cytoplasm is what we call the living contents of a cell without layers or the equivalent of a nucleus. Cytoplasm is a viscoelastic thixotropic gel.
Visco-elastic properties and thixotropy are possible only when the molecules form a continuous network that can break down and reappear. The destruction of the molecular network leads to the manifestation of liquid properties, and its restoration leads to the properties characteristic of solids. In the cytoplasm, elements that can be woven into a network are long filamentous microfilaments from the actin protein, which are probably held together by some other protein. When the molecules of this protein are cleaved, the network disintegrates (sol state). The microfilaments are now free to move, and thus the flow of protoplasm occurs, which can be found in most cells.
2. The structure of the cytoplasmic matrix
The cytoplasmic matrix provides a homogeneous (when examined under an electron microscope) substance between the microfilaments. It consists of water and many dissolved inorganic and organic substances, in particular enzymes and other proteins. The cytoplasmic matrix serves as a medium for the diffusion of many intermediate metabolic products, as well as a place where the most important metabolic processes such as glycolysis and the pentose phosphate cycle.
concept "cytosol" means the homogenate fraction that does not precipitate during ultracentrifugation, which contains the cytoplasmic matrix and very light structures, such as microfilaments. It is also applicable to the corresponding fraction of intact cells, although in the cell the matrix is not a sol, but, like the rest of the cytoplasm, is a viscoelastic thixotropic gel.
3. Characterization of ribosomes
Ribosomes carry out protein biosynthesis, thus realizing genetic information. Each cell has tens of thousands or millions of these tiny, 20–30 nm in size, rounded ribonucleoprotein particles. The ribosome consists of two unequal subparticles. They are formed separately and combined into mRNA, which occurs through an eccentrically located channel between the subparticles and delivers information for protein biosynthesis. In this case, several ribosomes can be linked by a thread-like mRNA molecule into a polysome (polyribosome) like a string of pearls.
Larger ribosomes we find in the cytoplasm of eukaryotic cells. Together with mRNA they can be associated with the endoplasmic reticulum. Their subparticles are synthesized in cell nucleus. Prokaryotic cells have smaller ribosomes. Ribosomes are extremely rich in magnesium.
4. Plasmids
Plasmids are very short DNA double helixes located outside the genome, closed in a ring (from a few to a hundred thousand base pairs in length), with one or more genes, and sometimes no genes at all. They replicate in most cases independently of the rest of the genetic material and often move from one cell to another. Currently, they are found in bacteria and yeast, as well as in the mitochondria of eukaryotic cells. Some bacterial plasmids can be included in the genome and again separated from it.
Question 18
1. Structure
Protoplasm limited outer membrane- plasmolemma and contains a system of internal membranes (endomembranes). Mitochondria and plastids, which also have internal membranes and a cell nucleus, are surrounded by two membranes.
The membrane thickness is most often 6-12 nm. Membranes delimit closed volumes of various sizes and shapes, such as vesicles, flattened cavities, or entire cells. Thus, creating an obstacle to diffusion, they form separate reaction volumes (compartments). On the other hand, membranes are able to selectively pass some substances and actively pump others, which is associated with energy consumption. It is believed each membrane separates the protoplasmic space from the non-plasmic space: the plasmolemma from the environment surrounding the cell, the membranes of the vesicles from the non-plasmatic contents of these vesicles, both membranes of the nuclear envelope from the non-plasmatic space located between them.
membranes(with the exception of mitochondrial and plastid membranes) are used in ontogenesis processes and can transform into each other (membrane flow). For example, the membranes of the Golgi apparatus are formed from the endoplasmic reticulum, and the latter serve as material for the regeneration of the plasmolemma.
2. Proteins and lipids in the membrane
The membranes are two-dimensional liquid crystal solutions of globular proteins in lipids. The structural basis of membranes is made up of lipids, among which phospholipids (for example, lecithin) predominate, and glycolipids in plastid membranes. Proteins in membranes perform certain functions: they are, for example, enzymes or transport proteins. In addition, the membranes include sterols (in animals, mainly cholesterol), glycoproteins, and some inorganic salts.
3. Basic structure of membranes
The basic structure of all membranes is two parallel layers of lipids (bimolecular layer). Membrane lipids are amphipathic molecules that have a hydrophobic part (hydrocarbon residues of fatty acids and sphingosine) and a hydrophilic part (phosphate, choline, comamine, sugar, etc.). Such molecules form on the water surface monolayer layer. In the aqueous environment and in the cell, bimolecular layers are formed: the hydrophobic parts of the various molecules are turned further away from the aqueous environment, i.e., towards each other, and are held together by strong hydrophobic interactions and weak van der Waals forces.
Thus, the membranes on both outer surfaces are hydrophilic, while on the inside they are hydrophobic. Since the hydrophilic parts of the molecules absorb electrons, they are visible in the electron microscope as two dark layers.
4. Effect of Temperature on the Membrane
At low temperatures hydrocarbon residues form a semblance of a crystal lattice, and the membranes go into a gel state. At physiological temperatures, the membranes are in a liquid-crystalline state: hydrocarbon residues rotate around their longitudinal axis and diffuse in the plane of the layer; less often jump from one layer to another without violating strong hydrophobic bonds.
Peripheral membrane proteins are hydrophilic, since hydrophilic amino acids (with polar groups) predominate on the surface of their globular molecule. They are relatively loosely bound to the hydrophilic surfaces of the membranes mainly by electrostatic forces, i.e., ionic bonds.
Integral membrane proteins hydrophobic (at least partially), since on the surface of their molecules are mainly hydrophobic amino acid residues.
These proteins are firmly fixed in the hydrophobic thickness of the membrane by hydrophobic interactions, and the hydrophilic parts of the molecules protrude from the membrane to the outside. Some integral membrane proteins are capable, like lipid molecules, of diffuse in the plane of the membrane, others are immobile.
Described fluid mosaic the membrane structure model (the Singer model) replaced the earlier Danieli model (without integral proteins).
Due to hydrophobic interactions, membranes are able to stretch (grow) when new molecules are included, and in case of rupture, the formed edges can close again.
The membranes are semi-permeable; they must have tiny pores through which water and other small hydrophilic molecules can diffuse. Probably, internal hydrophilic regions of integral membrane proteins or holes between adjacent integral proteins (tunnel proteins) are used for this.
Question 19
1. Characteristics of plasma membranes
The plasmalemma, whose thickness is about 8 nm, plays the role barrier for diffusion of substances from the cell; this is also essential for plant cells, since the cell wall is, as a rule, permeable. Transport molecules built into the membrane carry out the transfer of certain substances. Membrane enzymes accept only limited participation in metabolism. In plants, the plasmolemma is involved in the exchange of cell wall components, and in nerve cells, in the conduction of impulses.
During cell division daughter cells receive the plasma membrane from the parent cell. With the growth of the plasmolemma (associated with cell division and growth) and during its regeneration, it is formed from the Golgi vesicles (membrane flow).
plasma membrane animal cells are covered on the outside with a polysaccharide layer with a thickness of 10 to 20 nm - glycocalyx. Branched polysaccharide residues are covalently linked to proteins and sphingosine-containing lipids. The polysaccharides consist mainly of galactose, mannose, fucose, N-acetylgalactosamine, N-acetylglucosamine and (at the terminal positions) sialic acid residues. Sialic acids called N-glycosyl- and N-acetylneuraminic acids; neuraminic acid is a cyclic condensate of mannose and pyruvate.
From components glycocalyx the glycoprotein glycophorin in erythrocyte membranes has been well studied. It consists of 60% carbohydrates and carries (like other glycoproteins and glycolipids of the plasma membranes of animal cells) specific blood group antigens, as well as sites that bind various viruses and lectins.
Carboxyl end polypeptide chain protrudes from the membrane with its inside, and with outer side there is an amine end with numerous highly branched side chains of polysaccharides.
2. Difference of the plasma membrane in prokaryotic cells
The plasma membrane of prokaryotic cells differs in that it contains electron carriers and enzymes of the respiratory chain as integral proteins and forms various kinds of protrusions. Some protrusions carry out respiration, others - photosynthesis and respiration. Bacterial mesosomes are lamellar, tubular, or vesicular bodies lying in membrane pockets. The inner space of the mesosomes partially communicates with the extracellular environment. Mesosomes are formed as a result of complex folding and fusion of invaginated sections of the membrane. Their function is unknown. Similar structures have been described in blue-green algae and in fungal cells (although the latter are eukaryotic).
Question 20. Endoplasmic reticulum (ER)
1. ER characteristic
Tubular or compacted cisterns of the ER penetrate the entire cytoplasm and surround the cell nucleus, forming the nuclear envelope. Bubble-like extensions reach 100 nm in diameter. Many or even all cisterns are connected to each other and to the nuclear envelope, and their interior communicates with the perinuclear space. In plants, tubular cisterns extend through the cell wall into neighboring cells (desmotubules in desmosomes).
Tanks can not be selected entirely, since during homogenization they are destroyed to microsomes - fragments the size of a ribosome. Biochemical analysis ER is most often performed on preparations of microsomes.
Tank membranes have a thickness about 6 nm. Their constituent lipids are mainly glycerophosphatides (90–95%), in particular lecithin (55%).
2. Granular ER
granular (rough) The ER is densely dotted with polysomes, and the smooth (agranular) ER, consisting mainly of tubular elements, is not associated with them. Dense layers of cisterns of granular ER - the so-called ergastoplasm - are stained with basic dyes due to high content nucleic acids, so accumulations of these cisterns are visible under a light microscope, especially in cells that secrete proteins (in salivary glands and pancreas).
In granular ER certain proteins are synthesized. Ribosomes, attached by their large subparticles to the membrane, push newly synthesized polypeptide chains into cisterns, from where proteins are excreted from the cell, most often with the help of tubular cisterns of the smooth ER.
3. Smooth ER
In a smooth ER, various stages of the metabolism of carbohydrates, fatty acids, fats, terpenoids, and other substances take place. First of all, it is a center for the synthesis of lipids and membrane steroids (cholesterol) and thus the starting point for the flow of membranes, i.e., the formation and regeneration of the entire system of endomembrane and plasma membrane. IN muscle cells ER called here sarcoplasmic reticulum, serves the motor function.
In rapidly growing animal cells (embryonic, cancerous) in the cytoplasm and in the cell nucleus, annular membranes are found that are similar in structure to the nuclear membrane - short and flat isolated fragments of a double membrane with pores.
ER tanks can "multiply" by synthesizing their own structural components. In addition, they are apparently also formed from other membranes (for example, the Golgi cisterns) or as a result of the fusion of vesicles that detach from other parts of the ER.