The initial phase of mitosis is. Cell division

Prophase. During prophase, chromosomes condense and become visible under light microscopy. As DNP compacts, chromosomes acquire the structure of well-stained threads. The number of chromosomes is 4n, which corresponds to the amount of DNA 4c. Due to the inactivation of genes in the region of the nucleolar organizer and the inhibition of RNA synthesis in prophase, the disappearance of nucleoli is noted. The nuclear envelope gradually disintegrates into fragments and small membrane vesicles. At the same time, centrioles diverge to opposite poles of the cell.
In satellite site of the mother centriole the formation of microtubules begins, from which the filaments of the spindle are formed.

Metaphase. A characteristic event of metaphase is the movement of chromosomes to the equatorial plane of the spindle. Here they are located strictly regularly, forming a metaphase plate (when looking at the spindle from the side). If we consider a group of metaphase chromosomes from the side of the spindle poles, a figure resembling a star (the so-called mother star) clearly appears. During this period, it is possible to determine the number, shape and size of the chromosomes (d-chromosomes, double chromosomes) that make up the metaphase plate.
By the end of metaphase the longitudinal halves of the chromosomes (sister chromatids) are separated throughout, except for the zone of primary constriction.

For each type animals characterized by a strictly constant number of chromosomes in somatic cells. For humans, it is 46. The length of the chromosomes distinguishes between the alternation of colored and uncolored areas. Moreover, each chromosome has a unique pattern of differential coloring. Human chromosomes are divided into 7 groups according to their size and structural features (A, B, C, D, E, F, G) and each chromosome has its own number. The set of characteristics of the structure of chromosomes, their size and number constitutes what is called a karyotype.

Anaphase involves the process of divergence of chromosomes to the poles of a dividing cell. The mechanism of chromosome movement is explained by the sliding filament hypothesis, according to which spindle filaments consisting of microtubules, interacting with each other and with contractile proteins, pull chromosomes towards the poles. The speed of chromosome movement reaches 0.2-0.5 µm/min, and the entire anaphase lasts 2-3 minutes. Anaphase ends with the movement of two identical sets of chromosomes (s-chromosomes, or single chromosomes) to the poles, where they come together, forming figures that resemble appearance(when viewed from the pole) stars. These figures are called daughter stars.

Because chromosome stars are formed at each pole, this stage of mitosis is sometimes called the double star stage (diaster), or the stage of daughter stars. Telophase- the final stage of mitosis, during which daughter nuclei are reconstructed at the spindle poles. The rearrangement of telophase chromosomes resembles the processes of their change in prophase, but occurring in the opposite direction. When chromosomes interact with membrane vesicles of the cytoplasm, the nuclear envelope is formed. With the transition of chromosomes to the interphase state, new nucleoli are formed. Telophase ends with the division of the cell body - cytotomy, or cytokinesis, which leads to the formation of two daughter cells.

Part of the cells can exit the reproductive cycle and enter the path of differentiation. Some cells may exit the cell cycle in the G1 period or after the S period and remain at rest (Go period). Such resting cells retain the ability to divide and can again enter the reproduction cycle.

Educational video: cell mitosis and its stages

Time course of mitosis and cytokinesis typical of a mammalian cell. The exact numbers vary for different cells. Cytokinesis begins in anaphase and ends, as a rule,
by the end of telophase

The phase of the cell cycle corresponding to cell division is called M phase. The M-phase is conventionally divided into six stages, gradually and continuously transforming into one another. The first five - prophase, prometaphase, metaphase, anaphase and telophase - constitute mitosis, and the process of separation of the cell cytoplasm, or cytokinesis, which begins in anaphase, proceeds until the completion of the mitotic cycle and, as a rule, is considered part of telophase.

The duration of the individual stages is different and varies depending on the type of tissue, physiological state body, external factors. The longest stages are associated with the processes of intracellular synthesis: prophase and telophase. The most rapid phases of mitosis, during which the movement of chromosomes occurs: metaphase and anaphase. The actual process of chromosome divergence to the poles usually does not exceed 10 minutes.

Prophase

The main events of prophase include the condensation of chromosomes inside the nucleus and the formation of a division spindle in the cytoplasm of the cell. The disintegration of the nucleolus in prophase is a characteristic, but not obligatory, feature for all cells.

Conventionally, the beginning of prophase is taken to be the moment of the appearance of microscopically visible chromosomes due to the condensation of intranuclear chromatin. Chromosome compaction occurs due to multi-level DNA helixing. These changes are accompanied by an increase in the activity of phosphorylases that modify histones directly involved in DNA composition. As a consequence, the transcriptional activity of chromatin sharply decreases, nucleolar genes are inactivated, and most of the nucleolar proteins dissociate. Condensing sister chromatids in early prophase remain paired along their entire length with the help of cohesin proteins, but by the beginning of prometaphase, the connection between chromatids is maintained only in the centromere region. By late prophase, mature kinetochores are formed on each centromere of sister chromatids, necessary for chromosomes to attach to the microtubules of the spindle in prometaphase.

Along with the processes of intranuclear condensation of chromosomes, the mitotic spindle begins to form in the cytoplasm, one of the main structures of the cell division apparatus, responsible for the distribution of chromosomes between daughter cells. Polar bodies, microtubules and chromosome kinetochores take part in the formation of the division spindle in all eukaryotic cells.

The onset of mitotic spindle formation in prophase is associated with dramatic changes in the dynamic properties of microtubules. The half-life of the average microtubule decreases approximately 20-fold from 5 minutes to 15 seconds. However, their growth rate increases approximately 2 times compared to the same interphase microtubules. Polymerizing plus ends are “dynamically unstable” and change abruptly from uniform growth to rapid shortening, in which the entire microtubule often depolymerizes. It is noteworthy that for the proper functioning of the mitotic spindle, a certain balance between the processes of assembly and depolymerization of microtubules is necessary, since neither stabilized nor depolymerized spindle microtubules are able to move chromosomes.

Along with the observed changes in the dynamic properties of the microtubules that make up the spindle filaments, division poles are formed in prophase. Centrosomes replicated in the S phase diverge in opposite directions due to the interaction of pole microtubules growing towards each other. With their minus ends, the microtubules are immersed in the amorphous substance of the centrosomes, and polymerization processes occur from the plus ends facing the equatorial plane of the cell. In this case, the probable mechanism of pole separation is explained as follows: dynein-like proteins orient the polymerizing plus ends of polar microtubules in a parallel direction, and kinesin-like proteins, in turn, push them towards the division poles.

In parallel with the condensation of chromosomes and the formation of the mitotic spindle, during prophase, fragmentation of the endoplasmic reticulum occurs, which breaks up into small vacuoles, which then diverge to the periphery of the cell. At the same time, ribosomes lose connections with the ER membranes. The cisternae of the Golgi apparatus also change their perinuclear localization, breaking up into individual dictyosomes distributed in the cytoplasm in no particular order.

Prometaphase

Prometaphase

The end of prophase and the onset of prometaphase are usually marked by the disintegration of the nuclear membrane. A number of lamina proteins are phosphorylated, as a result of which the nuclear envelope fragments into small vacuoles and the pore complexes disappear. After the destruction of the nuclear membrane, the chromosomes are located in the nuclear region without any particular order. However, soon they all begin to move.

In prometaphase, intense but random movement of chromosomes is observed. Initially, individual chromosomes rapidly drift to the nearest pole of the mitotic spindle at a speed reaching 25 μm/min. Near the division poles, the probability of interaction of newly synthesized spindle microtubule plus ends with chromosome kinetochores increases. As a result of this interaction, kinetochore microtubules are stabilized from spontaneous depolymerization, and their growth partly ensures the removal of the chromosome connected to them in the direction from the pole to the equatorial plane of the spindle. On the other side, the chromosome is overtaken by strands of microtubules coming from the opposite pole of the mitotic spindle. By interacting with kinetochores, they also participate in chromosome movement. As a result, sister chromatids become associated with opposite poles of the spindle. The force developed by microtubules from different poles not only stabilizes the interaction of these microtubules with kinetochores, but also ultimately brings each chromosome into the plane of the metaphase plate.

In mammalian cells, prometaphase usually occurs within 10-20 minutes. In grasshopper neuroblasts, this stage takes only 4 minutes, and in the endosperm of Haemanthus and in newt fibroblasts it takes about 30 minutes.

Metaphase

Metaphase

At the end of prometaphase, the chromosomes are located in the equatorial plane of the spindle at approximately equal distances from both poles of division, forming a metaphase plate. The morphology of the metaphase plate in animal cells, as a rule, is distinguished by an ordered arrangement of chromosomes: the centromeric regions face the center of the spindle, and the arms face the periphery of the cell. IN plant cells chromosomes often lie in the equatorial plane of the spindle without strict order.

Metaphase occupies a significant part of the period of mitosis, and is characterized by a relatively stable state. All this time, the chromosomes are held in the equatorial plane of the spindle due to the balanced tension forces of kinetochore microtubules, performing oscillatory movements with insignificant amplitude in the plane of the metaphase plate.

In metaphase, as well as during other phases of mitosis, active renewal of spindle microtubules continues through intensive assembly and depolymerization of tubulin molecules. Despite some stabilization of the bundles of kinetochore microtubules, there is a constant reassembly of interpolar microtubules, the number of which reaches a maximum in metaphase.

By the end of metaphase, a clear separation of sister chromatids is observed, the connection between which is maintained only in the centromeric regions. The chromatid arms are parallel to each other, and the gap separating them becomes clearly visible.

Anaphase

Anaphase is the shortest stage of mitosis, which begins with the sudden separation and subsequent separation of sister chromatids towards opposite poles of the cell. Chromatids diverge at a uniform speed reaching 0.5-2 µm/min, and they often take a V-shape. Their movement is driven by significant forces, estimated at 10 dynes per chromosome, which is 10,000 times the force required to simply move a chromosome through the cytoplasm at the observed speed.

Typically, chromosome segregation in anaphase consists of two relatively independent processes called anaphase A and anaphase B.

Anaphase A is characterized by the separation of sister chromatids to opposite poles of cell division. The same forces that previously held the chromosomes in the plane of the metaphase plate are responsible for their movement. The process of chromatid separation is accompanied by a reduction in the length of depolymerizing kinetochore microtubules. Moreover, their decay is observed mainly in the region of kinetochores, from the plus ends. Probably, depolymerization of microtubules at kinetochores or in the region of division poles is a necessary condition for the movement of sister chromatids, since their movement stops with the addition of taxol or heavy water, which have a stabilizing effect on microtubules. The mechanism underlying chromosome segregation in anaphase A remains unknown.

During anaphase B, the poles of cell division themselves diverge, and, unlike anaphase A, this process occurs due to the assembly of polar microtubules from the plus ends. The polymerizing antiparallel filaments of the spindle, when interacting, partly create a force pushing the poles apart. The magnitude of the relative movement of the poles in this case, as well as the degree of overlap of polar microtubules in the equatorial zone of the cell, varies greatly among individuals different types. In addition to pushing forces, the division poles are affected by pulling forces from astral microtubules, which are created as a result of interaction with dynein-like proteins on the plasma membrane of the cell.

The sequence, duration, and relative contribution of each of the two processes that make up anaphase can be extremely different. Thus, in mammalian cells, anaphase B begins immediately after the start of chromatid divergence to opposite poles and continues until the mitotic spindle lengthens by 1.5-2 times compared to the metaphase one. In some other cells, anaphase B begins only after the chromatids reach the division poles. In some protozoa, during anaphase B, the spindle lengthens 15 times compared to the metaphase one. Anaphase B is absent in plant cells.

Telophase

Telophase

Telophase is considered the final stage of mitosis; its beginning is taken to be the moment the separated sister chromatids stop at the opposite poles of cell division. In early telophase, decondensation of chromosomes and, consequently, an increase in their volume are observed. Near the grouped individual chromosomes, the fusion of membrane vesicles begins, which begins the reconstruction of the nuclear envelope. The material for constructing the membranes of newly formed daughter nuclei are fragments of the initially disintegrated nuclear membrane of the mother cell, as well as elements of the endoplasmic reticulum. In this case, individual vesicles bind to the surface of the chromosomes and fuse together. The outer and inner nuclear membranes are gradually restored, the nuclear lamina and nuclear pores are restored. During the process of nuclear membrane restoration, discrete membrane vesicles probably connect to the surface of chromosomes without recognizing specific nucleotide sequences, since as a result of experiments it was revealed that nuclear membrane restoration occurs around DNA molecules borrowed from any organism, even from bacterial virus. Inside the newly formed cell nuclei, chromatin becomes dispersed, RNA synthesis resumes, and nucleoli become visible.

In parallel with the processes of formation of the nuclei of daughter cells in telophase, the disassembly of spindle microtubules begins and ends. Depolymerization proceeds in the direction from the division poles to the equatorial plane of the cell, from minus ends to plus ends. In this case, microtubules persist longest in the middle part of the spindle, which form the residual Fleming body.

The end of telophase predominantly coincides with the separation of the mother cell body by cytokinesis. In this case, two or more daughter cells are formed. The processes leading to the separation of the cytoplasm begin in the middle of anaphase and can continue after the completion of telophase. Mitosis is not always accompanied by division of the cytoplasm, therefore cytokinesis is not classified as a separate phase of mitotic division and is usually considered as part of telophase.

There are two main types of cytokinesis: division by transverse cell constriction and division by formation of a cell plate. The plane of cell division is determined by the position of the mitotic spindle and runs at right angles to the long axis of the spindle.

When a cell divides by a transverse constriction, the site of cytoplasmic division is preliminarily laid down during anaphase, when a contractile ring of actin and myosin filaments appears in the plane of the metaphase plate under the cell membrane. Subsequently, due to the activity of the contractile ring, a cleavage furrow is formed, which gradually deepens until the cell is completely divided. At the end of cytokinesis, the contractile ring completely disintegrates, and the plasma membrane contracts around a residual Fleming body, consisting of an accumulation of remnants of two groups of polar microtubules, closely packed together with dense matrix material.

Division by formation of the cell plate begins with the movement of small membrane-bound vesicles towards the equatorial plane of the cell. Here they merge to form a disc-shaped, membrane-surrounded structure called the early cell plate. The small vesicles originate primarily from the Golgi apparatus and move toward the equatorial plane along the residual pole microtubules of the spindle, forming a cylindrical structure called the phragmoplast. As the cell plate expands, the microtubules of the early phragmoplast simultaneously move to the periphery of the cell, where, due to new membrane vesicles, the growth of the cell plate continues until its final fusion with the membrane of the mother cell. After the final separation of the daughter cells, cellulose microfibrils are deposited in the cell plate, completing the formation of a rigid cell wall.

Mitosis(from the Greek mitos - thread), a method of dividing cell nuclei, ensuring identical distribution of genetic material between daughter cells and continuity of chromosomes in a number of cell generations. Mitosis is often called the process of division of not only the nucleus, but also the entire cell.

To study the mitotic activity of cells it is used mitotic index - the ratio of the number of cells undergoing mitosis in a certain period of time to total number cells that are present in the population at this moment. The younger the elements of erythropoiesis and leukopoiesis, the higher their mitotic index. According to various data, the mitotic index of the bone marrow can normally range from 1.0..6.0‰ to 7.6..13.1‰. Number of erythroid mitoses per bone marrow significantly exceeds the number of myeloid ones.

Mitosis consists of the following phases of varying duration:

• prophase;
• metaphase;
• anaphase (the shortest);
• telophase.

Thin threads (prophase chromosomes) begin to form in the nucleus, which then shorten and thicken, the nuclear membrane is destroyed, and a spindle is formed.

(the “mother star” stage, when the centromeric regions of the chromosomes face the center of the spindle) - all the chromosomes gather in the central part of the spindle, forming a metaphase plate.

Chromosomes lose centromeric connections, and two sets of chromosomes (identical) move to opposite poles of the cell.

Telophase- begins with the moment the chromosomes stop and ends with the division of the original cell into two daughter cells.

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The cell reproduces by division. There are two methods of division: mitosis and meiosis.

Mitosis(from the Greek mitos - thread), or indirect cell division, is a continuous process, as a result of which first doubling occurs, and then uniform distribution hereditary material, contained in chromosomes, between two formed cells. This is its biological significance. Nuclear division entails division of the entire cell. This process is called cytokinesis (from the Greek cytos - cell).

The state of the cell between two mitoses is called interphase, or interkinesis, and all changes that occur in it during preparation for mitosis and during the period of division are called the mitotic, or cell cycle.

Different cells have different mitotic cycles. Most of the time the cell is in a state of interkinesis; mitosis lasts a relatively short time. In the general mitotic cycle, mitosis itself takes 1/25-1/20 of the time, and in most cells it lasts from 0.5 to 2 hours.

The thickness of the chromosomes is so small that when examining the interphase nucleus with a light microscope, they are not visible; it is only possible to distinguish chromatin granules in the knots of their twisting. An electron microscope made it possible to detect chromosomes in a non-dividing nucleus, although at this time they are very long and consist of two strands of chromatids, the diameter of each of which is only 0.01 microns. Consequently, the chromosomes in the nucleus do not disappear, but take the form of long and thin threads that are almost invisible.

During mitosis, the nucleus goes through four successive phases: prophase, metaphase, anaphase and telophase.

Prophase(from the Greek about - before, phase - manifestation). This is the first phase of nuclear division, during which structural elements appear inside the nucleus that look like thin double threads, which led to the name of this type of division - mitosis. As a result of the spiralization of chromonemas, chromosomes in prophase become denser, shortened and become clearly visible. By the end of prophase, it can be clearly observed that each chromosome consists of two chromatids closely touching each other. Subsequently, both chromatids are connected by a common area - the centromere and begin to gradually move towards the cell equator.

In the middle or at the end of prophase, the nuclear envelope and nucleoli disappear, the centrioles double and move towards the poles. A fission spindle begins to form from the material of the cytoplasm and nucleus. It consists of two types of threads: supporting and pulling (chromosomal). The supporting threads form the basis of the spindle; they stretch from one pole of the cell to the other. Traction threads connect the centromeres of the chromatids to the poles of the cell and subsequently ensure the movement of chromosomes towards them. The mitotic apparatus of the cell is very sensitive to various external influences. When exposed to radiation, chemicals and high temperatures, the cell spindle can be destroyed, and all sorts of irregularities in cell division occur.

Metaphase(from the Greek meta - after, phase - manifestation). In metaphase, chromosomes become highly compacted and acquire a specific shape characteristic of a given species. The daughter chromatids in each pair are separated by a clearly visible longitudinal cleft. Most chromosomes become double-armed. At the point of inflection - the centromere - they are attached to the spindle thread. All chromosomes are located in the equatorial plane of the cell, their free ends are directed towards the center of the cell. Chromosomes are best observed and counted at this time. The cell spindle is also very clearly visible.

Anaphase(from the Greek ana - up, phase - manifestation). In anaphase, following the division of the centromeres, the chromatids, which have now become separate chromosomes, begin to separate to opposite poles. In this case, the chromosomes have the form of various hooks, with their ends facing the center of the cell. Since two completely identical chromatids arose from each chromosome, the number of chromosomes in both resulting daughter cells will be equal to the diploid number of the original mother cell.

The process of centromere division and movement to different poles of all newly formed paired chromosomes is characterized by exceptional synchrony.

At the end of anaphase, the chromonemal threads begin to unwind, and the chromosomes that have moved to the poles are no longer visible so clearly.

Telophase(from Greek telos - end, phase - manifestation). In telophase, the despiralization of chromosome threads continues, and the chromosomes gradually become thinner and longer, approaching the state in which they were in prophase. A nuclear envelope is formed around each group of chromosomes and a nucleolus is formed. At the same time, cytoplasmic division is completed and a cell septum appears. Both new daughter cells enter interphase.

The entire process of mitosis, as already noted, takes no more than 2 hours. Its duration depends on the type and age of the cells, as well as on the external conditions in which they are located (temperature, light, air humidity, etc.). Negatively affects the normal course of cell division high temperatures, radiation, various drugs and plant poisons (colchicine, acenaphthene, etc.).

Mitotic cell division is distinguished by a high degree of accuracy and perfection. The mechanism of mitosis was created and improved over many millions of years of evolutionary development of organisms. In mitosis, one of the most important properties of the cell as a self-governing and self-reproducing living biological system finds its manifestation.

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Mitosis (indirect division) is the division of somatic cells (cells of the body). The biological significance of mitosis is the reproduction of somatic cells, the production of copy cells (with the same set of chromosomes, with exactly the same hereditary information). All somatic cells in the body are derived from a single parent cell (zygote) through mitosis.

1) Prophase

• chromatin spirals (twists, condenses) into chromosomes
• nucleoli disappear
• the nuclear envelope disintegrates
• Centrioles diverge to the cell poles, a spindle is formed

2) Metaphase- chromosomes line up along the equator of the cell, a metaphase plate is formed

3) Anaphase- daughter chromosomes separate from each other (chromatids become chromosomes) and move towards the poles

4) Telophase

• chromosomes despiral (unwind, decondense) to the state of chromatin
• the nucleus and nucleoli appear
• spindle filaments are destroyed
• cytokinesis occurs - the division of the cytoplasm of the mother cell into two daughter cells

The duration of mitosis is 1-2 hours.

Cell cycle

This is the period of a cell’s life from the moment of its formation through the division of the mother cell until its own division or death.

The cell cycle consists of two periods:

• interphase(the state when the cell does NOT divide);
• division (mitosis or).

Interphase consists of several phases:

• presynthetic: the cell grows, active synthesis of RNA and proteins occurs in it, and the number of organelles increases; in addition, preparation for DNA doubling occurs (accumulation of nucleotides)
• synthetic: doubling (replication, reduplication) of DNA occurs
• postsynthetic: the cell prepares for division, synthesizes substances necessary for division, for example, spindle proteins.

MORE INFORMATION:
PART 2 ASSIGNMENTS:

Tests and assignments

Choose one, the most correct option. The process of reproduction of cells of organisms of different kingdoms of living nature is called
1) meiosis
2) mitosis
3) fertilization
4) crushing

Answer

1. All of the following features, except two, can be used to describe the processes of interphase of the cell cycle. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) cell growth
2) divergence of homologous chromosomes
3) arrangement of chromosomes along the equator of the cell
4) DNA replication
5) synthesis of organic substances

Answer

2. All of the following features, except two, can be used to describe the processes occurring in interphase. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) DNA replication
2) formation of the nuclear membrane
3) chromosome spiralization
4) ATP synthesis
5) synthesis of all types of RNA

Answer

3. The processes listed below, except two, are used to characterize interphase of the cell cycle. Identify two processes that “fall out” from the general list and write down the numbers under which they are indicated.
1) formation of the spindle
2) ATP synthesis
3) replication
4) cell growth
5) crossing over

Answer

Choose one, the most correct option. At what stage of life do chromosomes spiral into cells?
1) interphase
2) prophase
3) anaphase
4) metaphase

Answer

Choose three options. Which cell structures undergo the greatest changes during mitosis?
1) core
2) cytoplasm
3) ribosomes
4) lysosomes
5) cell center
6) chromosomes

Answer

1. Establish the sequence of processes occurring in a cell with chromosomes in interphase and subsequent mitosis
1) arrangement of chromosomes in the equatorial plane
2) DNA replication and formation of two-chromatid chromosomes
3) chromosome spiralization
4) divergence of sister chromosomes to the cell poles

Answer

2. Establish the sequence of processes occurring during interphase and mitosis. Write down the corresponding sequence of numbers.
1) spiralization of chromosomes, disappearance of the nuclear envelope
2) divergence of sister chromosomes to the cell poles
3) formation of two daughter cells
4) doubling of DNA molecules
5) placement of chromosomes in the plane of the cell equator

Answer

3. Establish the sequence of processes occurring in interphase and mitosis. Write down the corresponding sequence of numbers.
1) dissolution of the nuclear membrane
2) DNA replication
3) destruction of the fission spindle
4) divergence of single-chromatid chromosomes to the cell poles
5) formation of a metaphase plate

Answer

4. Establish the correct sequence of processes occurring during mitosis. Write down the numbers under which they are indicated.
1) decay of the nuclear shell
2) thickening and shortening of chromosomes
3) alignment of chromosomes in the central part of the cell
4) the beginning of the movement of chromosomes towards the center
5) divergence of chromatids to the cell poles
6) formation of new nuclear membranes

Answer

5. Establish the sequence of processes occurring during mitosis. Write down the corresponding sequence of numbers.
1) chromosome spiralization
2) chromatid divergence
3) formation of a fission spindle
4) despiralization of chromosomes
5) division of the cytoplasm
6) location of chromosomes at the equator of the cell

Answer

6. Establish the sequence of processes occurring during mitosis. Write down the corresponding sequence of numbers.
1) spindle threads are attached to each chromosome
2) the nuclear envelope is formed
3) doubling of centrioles occurs
4) protein synthesis, increase in the number of mitochondria
5) the centrioles of the cell center diverge to the cell poles
6) chromatids become independent chromosomes

Answer

FORMING 7:

4) disappearance of spindle threads

Choose one, the most correct option. When a cell divides, a spindle is formed in
1) prophase
2) telophase
3) metaphase
4) anaphase

Answer

Choose one, the most correct option. Mitosis does NOT occur in prophase
1) dissolution of the nuclear membrane
2) formation of the spindle
3) chromosome doubling
4) dissolution of nucleoli

Answer

Choose one, the most correct option. At what stage of life do chromatid cells become chromosomes?
1) interphase
2) prophase
3) metaphase
4) anaphase

Answer

Choose one, the most correct option. Unspiralization of chromosomes during cell division occurs in
1) prophase
2) metaphase
3) anaphase
4) telophase

Answer

Choose one, the most correct option. In what phase of mitosis are pairs of chromatids attached by their centromeres to the filaments of the spindle?
1) anaphase
2) telophase
3) prophase
4) metaphase

Answer

Establish a correspondence between the processes and phases of mitosis: 1) anaphase, 2) telophase. Write numbers 1 and 2 in the correct order.
A) the nuclear envelope is formed
B) sister chromosomes diverge to the poles of the cell
C) the spindle finally disappears
D) chromosomes despiral
D) chromosome centromeres separate

Answer

Establish a correspondence between the characteristics and phases of mitosis: 1) metaphase, 2) telophase. Write numbers 1 and 2 in the order corresponding to the letters.
A) Chromosomes consist of two chromatids.
B) Chromosomes despiral.
C) The spindle strands are attached to the centromere of the chromosomes.
D) The nuclear envelope is formed.
D) Chromosomes line up in the equatorial plane of the cell.
E) The division spindle disappears.

Answer

Establish a correspondence between the characteristics and phases of cell division: 1) anaphase, 2) metaphase, 3) telophase. Write numbers 1-3 in the order corresponding to the letters.
A) despiralization of chromosomes
B) number of chromosomes and DNA 4n4c
B) arrangement of chromosomes along the equator of the cell
D) divergence of chromosomes to the poles of the cell
D) connection of centromeres with spindle filaments
E) formation of the nuclear membrane

Answer

All but two of the characteristics listed below are used to describe the phase of mitosis shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) the nucleolus disappears
2) a fission spindle is formed
3) DNA molecules double
4) chromosomes are actively involved in protein biosynthesis
5) chromosomes spiral

Answer

Choose one, the most correct option. What is accompanied by the spiralization of chromosomes at the beginning of mitosis?
1) acquisition of a dichromatide structure
2) active participation of chromosomes in protein biosynthesis
3) doubling the DNA molecule
4) increased transcription

Answer

Establish a correspondence between the processes and periods of interphase: 1) postsynthetic, 2) presynthetic, 3) synthetic. Write down the numbers 1, 2, 3 in the order corresponding to the letters.
A) cell growth
B) ATP synthesis for the fission process
B) ATP synthesis for the replication of DNA molecules
D) synthesis of proteins to build microtubules
D) DNA replication

Answer

1. All of the following features, except two, can be used to describe the process of mitosis. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) underlies asexual reproduction
2) indirect division
3) provides regeneration
4) reduction division
5) genetic diversity increases

Answer

2. All of the above characteristics, except two, can be used to describe the processes of mitosis. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) formation of bivalents
2) conjugation and crossing over
3) constancy of the number of chromosomes in cells
4) formation of two cells
5) preservation of chromosome structure

Answer

All of the signs listed below, except two, are used to describe the process shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) daughter cells have the same set of chromosomes as parent cells
2) uneven distribution of genetic material between daughter cells
3) provides growth
4) formation of two daughter cells
5) direct division

Answer

All but two of the processes listed below occur during indirect cell division. Identify two processes that “fall out” from the general list and write down the numbers under which they are indicated.
1) two diploid cells are formed
2) four haploid cells are formed
3) somatic cell division occurs
4) conjugation and crossing over of chromosomes occurs
5) cell division is preceded by one interphase

Answer

1. Establish correspondence between stages life cycle cells and processes. Occurring during them: 1) interphase, 2) mitosis. Write numbers 1 and 2 in the order corresponding to the letters.
A) the spindle is formed
B) the cell grows, active synthesis of RNA and proteins occurs in it
B) cytokinesis occurs
D) the number of DNA molecules doubles
D) chromosome spiralization occurs

Answer

2. Establish a correspondence between the processes and stages of the cell life cycle: 1) interphase, 2) mitosis. Write numbers 1 and 2 in the order corresponding to the letters.
A) chromosome spiralization
B) intensive metabolism
B) doubling of centrioles
D) divergence of sister chromatids to the cell poles
D) DNA reduplication
E) increase in the number of cell organelles

Answer

What processes occur in a cell during interphase?
1) protein synthesis in the cytoplasm
2) chromosome spiralization
3) synthesis of mRNA in the nucleus
4) reduplication of DNA molecules
5) dissolution of the nuclear membrane
6) divergence of the centrioles of the cell center to the cell poles

Answer

Determine the phase and type of division shown in the figure. Write two numbers in the order specified in the task, without separators (spaces, commas, etc.).
1) anaphase
2) metaphase
3) prophase
4) telophase
5) mitosis
6) meiosis I
7) meiosis II

Answer

All but two of the characteristics listed below are used to describe the stage of the cell life cycle shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) the spindle disappears
2) chromosomes form an equatorial plate
3) a nuclear membrane is formed around the chromosomes at each pole
4) separation of the cytoplasm occurs
5) chromosomes spiral and become clearly visible

Answer

Establish a correspondence between the processes and stages of cell division. Write numbers 1 and 2 in the order corresponding to the letters.
A) destruction of the nuclear membrane
B) chromosome spiralization
B) divergence of chromatids to the poles of the cell
D) formation of single chromatid chromosomes
D) divergence of centrioles to the cell poles

Answer

Look at the drawing. Indicate (A) the type of division, (B) the phase of division, (C) the amount of genetic material in the cell. For each letter, select the corresponding term from the list provided.
1) mitosis
2) meiosis II
3) metaphase
4) anaphase
5) telophase
6) 2n4c
7) 4n4c
8) n2c

Answer

All but two of the features listed below are used to describe the cellular structure shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) type of cell division - mitosis
2) phase of cell division - anaphase
3) chromosomes, consisting of two chromatids, are attached by their centromeres to the filaments of the spindle
4) chromosomes are located in the equatorial plane
5) crossing over occurs

Answer

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