Cytology. Cell division sequence of cell division stages

Shortly after the German Pathophysiologist R.virhov in the middle of the XIX century. Formulated the basic principle of cell theory in the form of aphorism Omni Cellula Ex Cellula ("Any cell - from a different cell"), it was found that the life of a somatic cell flows cyclically, starting with division and dividing ending. For a half a century, many new data on the features of the division of various cells were obtained. Many processes of organization and regulation of division are understood, their incredible complexity. And an increasing admiration of researchers causes the accuracy with which the chromosome is separated between future daughter cells. It is about the mechanisms of separation of chromosomes (on the example of animal cells) and will be discussed below.

Cell cycle - This sequence naturally replacing each other phases from cell formation as a result of dividing to either dividing it into subsidiaries in the next division act or death. Eukaritis the cell cycle consists of interphase and actually division, or mitosis. Each of these phases correspond to certain phenomena and processes that allow them to divide them into smaller stages. In different organisms, the number and sequence of the stages of the cell cycle differ.

Interfhaza It is much more durable than mitosis (usually occupies at least 90% of the total cell cycle time), and is usually divided into three periods: the pretenttic (G1), synthetic (S) and postsynthetic (G2). At the G2 stage, the cell can go to the next division or to rest condition (G0). The transition to the division is possible only from stage G2, therefore, if the cell is in a state G0, to continue the division, it is necessary to return to the state G2. The G1 stage can continue from 2 h to several weeks or even months, the duration of stage S 6-12 hours, and the G2 stage is from half an hour to several hours.

Actually indirect division , or mitosis consists of stages of carokines (core division) and cytokinesis (cytoplasm divisions). The chromosome separation occurs at the carokinosis stage, so we consider it more.

In the first phase of mitosis - pROFADE - chromosome spirals and become visible in the light microscope in the form of thin threads. Cell centers whose doubling occurs in stage S, diverge to the poles of the cell. At the end of the proofased, the nuclei disappear, the nuclear shell is destroyed and the chromosomes go to the cytoplasm.

The cell then goes into metafuzwhose start called promethaphase. In the chromosome semiosomes are located in a cytoplasm rather randomly. The mitotic apparatus is formed, which includes spine division and centrioli. The separato divisions is a system of special structures, microtubules (MT), in a dividing cell that provides a discrepancy to chromosomes. Then the kinetokhors (centromers) chromosomes are captured by MT, separated from both poles of the separation of division, and after some time the chromosome is built in the equatorial plane of the cell. In the metaphase chromosome, the most spiralized. The centeriers of chromosomes are located in the equatorial plane of the cell independently of each other. The combination of chromosomes in the equatorial plane of the cell forms a metaphase plate.

At the next stage of division - in anafhase - The chromosome on chromatide is separated. From this point on, each chromatide becomes an independent single chromosome. First, nursing chromatids diverge to the opposite poles of the separation of division, and the poles themselves remain stationary ( anafase A.), and then the poles of spindles are diverted to the opposite ends of the cell ( anphase B.).

After that, the cell goes into bulfase: The spindlers are destroyed, chromosome in the cell poles are despirate, nuclear shells are formed around them. Two cores are formed in the cage, genetically identical to the source kernel.

With the end of the carokinesis, the cell passes into the cytokinez stage, on which the cytoplasm is separated and the formation of diaphragm of child cells occurs. In animals, cytokines occurs by "rejected" cells. In plants, cytokines occurs differently: in the equatorial plane, bubbles are formed, which merge with the formation of two parallel membranes. This mitosis ends and subsidiaries go to interfase.

At all the stages of the carokinesis, MT is played, their education and spatial orientation, interaction with chromosomes, structural changes, creating the forces necessary for chromosome separation, and finally their destruction. MT is part of the cytoskeleton and play a crucial role in maintaining and changing the shape of the cell and the directional transfer of intracellular components (vesicle, organelle, proteins, etc.) in the cytoplasm. In animal cells, several thousand MT. All of them grow from special formations, called centers of the organization MT (COMT). The cell can be 1-2 com. Studies have shown that only a few dozen MTs depart from centrosome, therefore MT is not necessarily related to the centrosome. The centrioles also give the beginning of the new MT, which come to replace gradually depolymerizing the old.

Centrosoma, or cellular center, is the main COMT and the regulator of the cell cycle in eukaryotes. Centrosoma consists of amorphous material and a pair of centrilar - maternal and subsidiary, located strictly in a certain way and forming a structure called diplos. (The structure and functions of the centrosome can be read, for example, in the magazine "Nature", 2007, No. 5.) In addition to participating in the nucleus division, the centrosome plays an important role in the formation of flagella and cilia. Centrioles located in it perform the function of the organization's centers for MT axon of flagella. In organisms devoid of centrioles (for example, in sampling and basidy mushrooms, coated plants), flagellas do not develop.

COMUT can be reproduced independently: the new center is formed next to the existing one, and then moves away from it. Until now, the secret remained as happens. But quite recently, American scientists, studying extracts with a cereal of molluste oocytes Spisula Solidissima., found that the centrosome contain special RNA molecules. Given that the centrosome has a very ancient origin and extremely conservatives, this discovery suggested that they have their own genetic apparatus.

MT is a very small tube with a length of several micrometers with an outer diameter of 25 nm. It is built of 13 long "sticks" - protofilaments, parallel axis of the tube and arranged in a circle. The protofilament is made up of alpha and beta-tubulin globes, and in each pair of such a globul (dimer of tubulin) alpha tubulin interacts with beta tubulin, and beta-tubulin - with alpha tubulin of the nearest neighboring dimers, which allows for the formation of very strong Cylindrical design. How can such a design be moving anything inside the cell?

As for the organization, proteins and other cell components, they move on MT, attaching to Motor proteins: dinine and kinesins that are able to literally "walk" on MT in a certain direction, consuming ATP as fuel. The chromosomes are attached to the ends of MT, which then somehow quickly disappear to the poles of the separation of the division.

It was known that the length of MT can be constant, as, for example, in flagella. However, the length of the cytoplasmic MT is constantly changing: they are growing, it is shortened, they can disappear at all, then again begin to grow ... When MT in the process reaches the target, its length is stabilized, but as happens, it is still not quite clear.

It is experimentally established that MT may be in three main states: polymerization, depolymerization and disasters. Polymerization is the addition of single tubulin molecules, which are in cytoplasm, to the tube (depolymerization - reverse process). Alpha and beta subunits of dymeimers of tubulin in cytoplasm first attach one molecule of guanosintrifosphate (GTF), similar to the properties on ATP, and then can already join the target MT. To increase MT, some specific proteins, the presence of magnesium ions and the absence of calcium ions in the cytoplasm.

While two GTF molecules are associated with a dimeer of a tubulin, it is in T-state, and at the same time the entire design of the tube is stable. However, on a beta subunit of Dimer, the tubulin after a while there is a hydrolysis of GTF, which turns into guanosinediffosphate (GDF), while the entire dimer goes into the D-state, and the ring of tubulin molecules on the MT end becomes tense, unstable. In this state, the new dimers of tubulin can no longer join the Tubulin, and MT goes into the catastrophe state. Therefore, MT growth is possible only at the end of MT there is a Tubulin T-Dimer Ring, the so-called T-hat. If the concentration of tubulin in the cytoplasm is small, Dimers "T-Caps" may have time to go to the D-dimer, before they are joined by new T-dimers and the tube will switch to the state of the catastrophe.

If there is a disconnection of a tubulin molecules on the ring at the end of MT, then, with a catastrof, the protofilaments are separated, like individual wires, and strive to spin into rings. At the same time, the disassembly of MT occurs very quickly. The end of MT, fixed in the centrosome and protected from a catastrophe, is called "minus" - Conference MT, and the other end, which either increases, or quickly collapses - "plus" - Conception. In the cytoplasm there are many proteins that can interact with tubulin in different states, affecting the growth rate or the decay of MT. It is essential that proteins-motors can distinguish between "plus" - and "minus" - MTCs: Dinaines move to "minus" - Conference, and kinesins - to the "plus" -conic microtubule.

Each stage of mitosis corresponds to the special behavior of MT. The mitotic division occurs with the formation of a special structure - the separation of the division, the basis of the structure of which is MT, emanating from two cell centers located in the poles of the cell. The spindle divisions consists of two seashedral overlapping in the central part, at the ends of which are centrosome. In vegetable cells, the formation of the separation of division occurs without participation in the centrosome. Therefore, three types of MT can be distinguished: astral, pole and kinetrochorny. Film-powered MT bind a centrosome with a chromosome kirethor. They are formed in the Promethaft. At the stage of early proofased, astral MTs are rapidly growing radially from each of the two cell centers. Astral MTs stretch from the centrosion to the periphery of the cell, their "plus" - the opposites interact with the proteins enshrined in the cell membrane, apparently, with the help of dinaines that attract centrosomes to the membrane.

At the same time, pole MT appear, which grow in the direction from one cellular center to another. Pole MT tend to unite in groups from two to six MT (at the metaphase stage), mainly from MT of the opposite pole. So the pole threads are formed, in which MT is directed by anti-parallel, i.e. "Plus" - the opposite parties. The motor proteins mentioned above, interacting with anti-parallel MT, lead either to the tightening of cell centers towards each other or to their swelling. The absence or defects of any of these motor proteins lead to violations of the divergence of centrosome and mitosis as a whole.

In addition to changes in the organization MT associated with the doubling of the centrosome, their dynamics changes. During MT interfhase relatively long and stable, the state of growth lasts an average of about 10 minutes. When moving to mitosis, the frequency of the catastrophe increases about 10 times, so the state of growth MT is shortened and becomes less than 1 min. These changes are caused mainly by special proteins that control the course of mitosis, and lead to the fact that MT become unstable, quickly changing.

Due to the fact that at the stage of the production phase, the nuclear membrane is already destroyed, MT can reach chromosomes. The accession of them to the kinetochetors occurs randomly, when contacting the kinetochora with a "plus" - Conference or the side surface of MT. In the latter case (lateral interaction) of the chromosome begins quickly, at a speed of 20-25 μm / min, move to the corresponding pole of the separation of division. This speed is comparable with the speed of moving Dienein along MT, but there are no direct data on the participation of Dienein in this process. Then the lateral interaction is replaced by the end due to the destruction of MT in the kineto chore, and the MT length is stabilized.

The kinetchor is a three-layer structure visible on micrographs as two dark layers separated by a light gap. It has a length of 0.3-0.6 μm and a thickness of about 0.1 μm. One dark layer of the kinetochora is associated with the centromer, the other - with MT. MTs that are not associated with the centrosome (in plant and some other cells, the spontaneous division are formed at all without a centrosome) can be attached to the kinetchore. The polarity of the accession of such MT is the same: "Plus" -Con is attached to the kinetochore, and "minus" - Conception is near the pole of spindle. Such MT are more stable than MT, ending in the poles of spindle division.

Directional transport of proteins inside the cell

At the beginning of mitosis, the chromosomes kinetochore are located asymmetrically relative to the poles of the separation of division, so they are quickly captured by MT, which come from the nearest pole. However, until the nursing kinetchor is captured by MT, coming from another pole, and the pair of chromosomes will not be located on the equator of spindle division, mitosis will not go to the next stage - anafase. This provide special proteins that are part of the system of control points of mitosis. There are several of such control points in the cell cycle. Only if the previous stage of mitosis is completed normally, they produce a ready signal to continue mitosis.

For each of their two kinetchors, nursing chromatids is attached 10-40 MT forming a digital thread. At the same time, the velocity of MT to kinetochetors increases by the end of the metaphase about 10 times compared with the Promethasa. This is explained by the fact that the MT who already joined the kinetchore make it easy to connect the following MT. This process is called cooperative.

Our certificate Violations of mitosis. With different pathological processes, the normal course of mitosis is broken. 3 main types of pathology are distinguished: 1) damage to chromosomes (swelling, gluing, fragmentation, formation of bridges, damage to centromers, lag of individual chromosomes when driving, violation of their spiralization and despiracylation, early separation of chromatids, formation of a microerider; 2) damage to the mitotic apparatus (mitosis delay in metaphase, multi-pole, monocentric and asymmetric mitosis, threegroup and high metaphase); 3) cytotomy violations. Pathological mitoses occur after the impact of mitotic poisons, toxins, extreme factors (ionizing radiation, anoxia, hypothermia), with viral infection and tumor. A sharp increase in the number of pathological mitoses is typically for malignant tumors.

The basic function of the separation of division is to ensure the correct separation of the nursing chromatide. For the directional movement of such large structures as chromatids, it is necessary for significant forces on them. Experiments show that there are several types of such forces.

Power of the first type There is due to the continuous buildup of "plus" -Conny MT and depolymerization "minus" - Conference. These processes (with equality of their speeds) lead to the fact that the dimems of the tubulin are continuously moved towards the "minus" -concar, and the length of the tube does not change. If you block the attachment of the tubulin to the "plus" -conception MT (the addition of taxi), then the disassembly of MT in centrosomas still continues and the centrosome is starting to move towards chromosomes at a rate determined by the depolymerization rate of MT. Determining the speed of movement of tubulin in such a MT showed that the force arising during this ensures up to 25% of the velocity of the chromosome movement to the pole of the separation of the division in the anatherapy. In an isolated frog eggs, the mitotic spindle movement of chromosomes is fully ensured by this force.

Forces of the second type ("Polar Wind") act on the sections of chromatid not related to the kinetchor. It is experimentally shown that after cutting off the shoulders with chromosomes from centromers, they begin to move to the equator spine separation at a speed of about 2 μm / min and in the end occupy the position between the poles of the division spine. Most likely, these forces are due to the interaction of protein-motors associated with chromatin (type of kinesin) with MT.

Finally, third type power - This is the power with which the kinetogo thread pulls the chromosome to the pole spine division. This is the main force that ensures the discrepancy of chromosomes in Anafase. It seems to be several components. First, the kinetokhore includes motor proteins (dyein), which can interact with the side surface of MT and cause the movement of the kirethor to the centrosome. Secondly, there are proteins that are able to significantly affect the growth rate or the destruction of MT depending on the signals of the control point system whose proteins are also in the kineto chore. After passing the control point and the transition of the cell in Anaphz, the depolymerization rate of MT in the kinetochora increases sharply. As a result, MT begins to quickly shrink, developing the necessary for the movement of chromosomes to the pole. In addition, the tension of the kinetrochorny threads increases even with their constant length due to the discrepancy between the anti-parallel sections of pole MT and, as a result, increase their length. The force generated by this process, the less, the greater the length of the pole MT: the elasticity of MT is finite, therefore, with an increase in length, they begin to bend, and the force that spreads the poles of the separation of the division is reduced. Consequently, the farther from each other are the poles of the separation of division, the smaller the power of them.

The balance of the forces listed above leads first to build chromosomes by the equator of the separation of division, and then, as a result of the change in the balance, to their discrepancy to the poles. It should be noted that the balance is dynamic, and not static, therefore, even with a stable location of chromosomes in the plane of the equator, the division is constantly shifted to one pole, then to another. The speed of such vibrational movements is 2-3 μm / min. While the exact model of these oscillations is not.

Briefly summarize the above. The most important task of mitosis is the correct separation of the nursing chromosomes, which is carried out with the help of the separation of division. The spindle divisions is formed by MT, with whom proteins - motors (dinaines and kinesins), kinetokhory, centrioles, membrane proteins interact. Proteins-motors can bind to proteins of various intracellular structures (for example, with chromatin) and ensure their movement over MT in one or the other side, carried out due to the energy of hydrolysis of ATP. The movement of chromosomes is ensured by both the interaction of MT with proteins-motors, and due to the processes of growth or the decay of MT. At the same time, it is the ratio of the speeds of the last two processes, adjustable by proteins of the control points system, provides, mainly, and build chromosomes in the equatorial plane, and the discrepancy between them is spinning the fission spin.

Although directly measuring the forces acting from MT on chromosome, it is not possible, many details of the molecular mechanisms of these processes will find out their adequate models. Recently, models that bind biochemical and mechanical processes during mitosis began to appear, but the decisive word, as always, remains for experimental studies that have yet to be fulfilled.

1. Similar structure of plants and animal cells - proof
A) their kinship
B) the generality of the origin of the organisms of all kingdoms
C) origin of plants from animals
D) complications of organisms in the process of evolution
E) unity of the organic world
E) manifolds of organisms

Answer

2. What functions perform the Golgji complex?
A) synthesizes organic substances from inorganic
B) splits biopolymers to monomers
C) accumulates proteins, lipids, carbohydrates synthesized in a cell
D) provides packaging and removal of substances from the cell
E) oxidizes organic substances to inorganic
E) participates in the formation of lysosomes

Answer

3. Set the correspondence between the characteristic of the body and the group for which it is characteristic: 1-prokaryotes, 2-viruses.
A) cellular body structure
B) the presence of own metabolism
C) embedding of own DNA in the DNA host cell
D) consists of nucleic acid and protein shell
E) division division
E) reverse transcription ability

Answer

A1 B1 B2 G2 D1 E2

4. The autotrops include
A) dispute plants
B) mold mushrooms
C) single-celled algae
D) chemotrophic bacteria
E) viruses
E) most of the simplest

Answer

5. Install the sequence of processes occurring during MEIOS
A) the location of pairs of homologous chromosomes in the equatorial plane
B) conjugation, crossinchinger homologous chromosomes
C) location in the plane of the equator and the discrepancy between the nursing chromosomes
D) the formation of four haploid cores
E) the discrepancy of homologous chromosomes

Answer

5a. What signs characterize meyosis?
A) the presence of two following one by one divisions
B) the formation of two cells with the same hereditary information
C) the discrepancy between homologous chromosomes in different cells
D) the formation of diploid daughter cells
E) lack of interphase before first division
E) conjugation and crossinchinger chromosome

Answer

6. Install the correspondence between the characteristic of the gamenenesis and its type: 1-ovogenesis, 2-spermatogenesis
A) one large sex cell is formed
B) Cereals are formed
C) a lot of small weights are formed
D) nutrients are inhibited in one of four cells
D) mobile games are formed

Answer

A1 B1 B2 g1 d2

7. Install the sequence of processes occurring in a cell with chromosomes in an interfass and subsequent mitosis
A) Location of chromosomes in the equatorial plane
B) DNA replication and formation of two-line chromosomes
C) chromosome spiralization
D) the discrepancy between the nursing chromosomes to the poles of the cell

Answer

7+. What cellular structures undergo the greatest changes in the mitosis process?
A) kernel
B) cytoplasm
C) Ribosomes
D) lysosomes
E) cell center
E) chromosomes

Answer

8. Install the correspondence between the structure of the organoid and its type: 1-cell center, 2-ribosome
A) consists of two perpendicularly located cylinders
B) consists of two subunits
C) formed by microtubes
D) Contains proteins that ensure the movement of chromosomes
E) contains proteins and nucleic acid

Answer

A1 B2 B1 G1 d2

9. Install the sequence of processes occurring in phagocytosis
A) the arrival of monomers in the cytoplasm
B) capture of cell membrane nutrients
C) hydrolysis of polymers to monomers
D) formation of phagocytous bubble inside the cell
E) foocitotic bubble fusion with lysosome

Answer

Answer

12. The main positions of cell theory make it possible to draw conclusions about
A) influence environment on fitness
B) kinship of organisms

D) the development of organisms from simple to complex

E) the possibilities of self-relocation of life from inanimate matter

Answer

12+. The main positions of cell theory make it possible to draw conclusions about
A) biogenic migration of atoms
B) kinship of organisms
C) the origin of plants and animals from the general ancestor
D) the appearance of life on Earth about 4.5 billion years ago
E) a similar structure of cells of all organisms
E) the relationship of living and inanimate nature

Answer

12 ++. What provisions contains cell theory?
A) new cells are formed as a result of the division of the maternal cell
B) in the genital cells contain a haploid set of chromosomes
C) cells are similar to chemical composition
D) cell - a unit of development of all organisms
E) tissue cells of all plants and animals are the same in structure
E) all cells contain DNA molecules

Answer

13. The similarity of the cells of mushrooms and animals is that they have
A) a shell of chitin-like substance
B) glycogen as a spare carbohydrate
C) decorated kernel
D) vacuole with cellular juice
E) mitochondria
E) plasts
A) form fabrics and organs
B) participate in the process of fertilization
C) always haploid
D) have a diploid set of chromosomes
E) are formed in the process of Maiz
E) divided by mitosis

Answer

A1 B2 B2 G1 D2 E1

17. What do mitochondria differ from Lizosom?
A) have an outdoor and internal membrane
B) have numerous growing cristes
C) participate in energy liberation processes
D) In \u200b\u200bthem, peyrogradic acid is oxidized to carbon dioxide and water
E) biopolymers split to monomers
E) participate in the metabolism

Answer

"Limit of a numerical sequence" - limited numerical sequence. Example: 1, 3, 5, 7, 9, 2P-1, ... is an increasing sequence. The function y \u003d f (x) is called continuous at the point x \u003d a if the condition is satisfied. The limit of the private is equal to the private limits: the concept of numerical sequence. The assignment of the analytical formula. The sequence of prime numbers: 2; 3; five; 7; eleven; 13; 17; nineteen; 23; 29; ...

"Mitz biology" - where does the education of a new multicellular body begins? Phase mitosis. Amitosis. Interphase. Questions for self-control. Meiosis. What does cell division in single-cell organisms lead? Studying a new material. Methods of cell division. What is the process of growing and developing the body begins? Cell division.

"Sequences" - called the first member of the sequence. Consider the sequence: - the formula of the N-head member of the arithmetic progression. After folding the equality (1) and (2), we obtain: denote the sum of the first members of the arithmetic progression through. The number of such steam is N. Methods for setting numerical sequences:

"The limits of sequences and functions" is a solution. Final task. Sequence and function limit. Objectives: Workbook at the end of the study to check for a teacher verification. Pay attention to how members of the sequence behave. Contained. Call the limit. Answer: Starting with N0 \u003d 4 All members of the sequence (xn) fall into the neighborhood (-0.1; 0.1).

"Sequence of numbers" - sequences are given by formulas: houses on the street. Sequences make up such elements of nature that can be numbered. Classes at school. Days of the week. Check yourself. Numeric sequences. An increase of 3 times. Between the numbers of Fibonacci and the triangle of Pascal there is a connection. Alternate an increase of 2 and an increase of 2 times.

"Mitz division of cells" - a nuclear sheath is destroyed. The formation of the separation of division, shortening chromosomes, the formation of an equatorial plate. Phases mitosis. With different pathological processes, the normal course of mitosis is broken. Mitosis. The formation of two identical subsidiaries. Bulfase. Profaise of metaphase equathasis Bulfase.

30. Perform the laboratory work "Observation of the cytoplasm movement" (see. 42-43 textbooks). Make appropriate drawings and signatures to them.

Conclusion: the cytoplasm movement and movement of organoids constantly occurs in the cell. Movement is a property of living. Thus, there is a movement in the cells of nutrients and air

31. After examining the text of the paragraph, fill out the "Cage Life Processes" scheme

The movement of the cytoplasm: the movement of nutrients and air

Breathing: oxygen flow occurs in a cage

Power supply: Nutrients obtained from soil and air enter the cell through the cellular shell in the form of solutions

Reproduction: cell division occurs for which the chromosome of the nucleus is responsible

Height: the size of the cell after division increases

32. Consider the plant cell division scheme. Specify the sequence of the stages (stages) of cell division

33. Specify the sequence of changes from the youngest to the oldest cell. What is the difference between the youngest cage from the oldest cell?

The core of the young cell is located in the center. In the old cell - one large vacuole, so the cytoplasm is tightly adjacent to the shell. In young cells a lot of small vacuoles and they are able to share

34. What is the importance of chromosome? Why are their number in a cage constantly?

Chromosome transmit hereditary information from the cell to the cell. Their number is constantly, as this is the characteristic of the species. During the division, their number is always doubled, and then evenly distributed between the daughter cells. Thus, the chromosomal set is preserved

35. Prove that the cell is a variety of plants

The cell has all the properties of the living: division (reproduction), breathing, food, metabolism, growth, development and aging