The life cycle of a cell: interphase (the period of cell preparation for division) and mitosis (division). Cell cycle. Preparation of the cell for division. Direct and indirect cell division. Mitosis, the biological essence and significance of mitosis

Target: to update the personal significance for students the importance for students of the issues of the topic under study, showing the biological significance of mitosis and meiosis

Tasks:

Create organizational conditions for fostering perseverance in achieving the goal;

Develop communication skills through work in small groups.

Equipment: a textbook, a computer (with Internet access), a multimedia projector, an Open Biology CD, reference literature on biology.

During the classes:

1. Determining the topic of the lesson.

Knowledge update

Students were given cards with a task: for each term indicated in the left column, select the corresponding definition given in the right column.

Answer: 1 - D, G; 2 - B; 3 - B; 4 - A; 5 - E

3. Learning new material

3.1 Teacher's story about mitosis (you can use the model of mitosis, which is available on the disc "Open Biology").

3.2 Independent work of students.

Prepare a story about meiosis using any sources of information (textbook, reference literature, Internet). As you work, remember! The ancient Roman orator Cicero believed that properly articulated speech contains answers to seven questions: What? Where, How?, When (under what conditions), What?, Why?, Why? Of course, it is not always possible to find an answer to all the questions of the algorithm, but we must try to answer most of the questions, and we must try to get a relatively related text (students work in groups, since the number of computers in the classroom is limited).

Possible sources of information:

K. Wiley Biology. - M.: Mir, 1966, translated from English, - 685 p.: ill.

Biology: A large reference book for schoolchildren and university applicants /, etc. - 3rd ed., stereotype. – M.: Bustard, 2000. - 668 p.: ill. - (Large reference books for schoolchildren and applicants to universities).

Biology. Big Encyclopedic Dictionary / Ch. ed. . - 3rd ed. - M.: Great Russian Encyclopedia, 1999. - 864 p. - ill., 30 sheets. col. ill.

Encyclopedia for children. T. 2. Biology / Comp. - 3rd ed. Revised And extra. – M.: Avanta+, 1996. – 704 p.: ill.

Web sites:

http://ru. wikipedia. org/wiki/%D0%9C%D0%B5%D0%B9%D0%BE%D0%B7

http://ru. wikipedia. org/wiki/%D0%9A%D0%BE%D0%BD%D1%8A%D1%8E%D0%B3%D0%B0%D1%86%D0%B8%D1%8F

http://ru. wikipedia. org/wiki/%D0%9C%D0%B8%D1%82%D0%BE%D0%B7

http://ru. wikipedia. org/wiki/%D0%96%D0%B8%D0%B7%D0%BD%D0%B5%D0%BD%D0%BD%D1%8B%D0%B9_%D1%86%D0%B8%D0 %BA%D0%BB

http://ru. wikipedia. org/wiki/%D0%9A%D1%80%D0%BE%D1%81%D1%81%D0%B8%D0%BD%D0%B3%D0%BE%D0%B2%D0%B5%D1 %80

"Open Biology"

3.3 Mutual check of tasks.

4. Reflection

Students were given cards. Fill in the table1

Using the results of the work, compare mitosis and meiosis

Think about whether environmental conditions can affect the processes of mitosis and meiosis? What consequences for the body can this lead to?

The textbook complies with the Federal State Educational Standard for Secondary (Complete) General Education, is recommended by the Ministry of Education and Science of the Russian Federation and is included in the Federal List of Textbooks.

The textbook is addressed to students in grade 10 and is designed to teach the subject 1 or 2 hours per week.

Modern design, multi-level questions and tasks, additional information and the possibility of parallel work with an electronic application contribute to the effective assimilation of educational material.

Remember!

How, according to the cell theory, does an increase in the number of cells occur?

Do you think that the lifespan of different types of cells in a multicellular organism is the same? Justify your opinion.

At the time of birth, a child weighs an average of 3–3.5 kg and is about 50 cm tall, a brown bear cub whose parents reach a weight of 200 kg or more weighs no more than 500 g, and a tiny kangaroo weighs less than 1 g. a beautiful swan grows up from a nestling, a nimble tadpole turns into a sedate toad, and a huge oak tree grows from an acorn planted near the house, which, after a hundred years, pleases new generations of people with its beauty. All these changes are possible due to the ability of organisms to grow and develop. The tree will not turn into a seed, the fish will not return to the egg - the processes of growth and development are irreversible. These two properties of living matter are inextricably linked with each other, and they are based on the ability of the cell to divide and specialize.

The growth of ciliates or amoeba is an increase in the size and complication of the structure of an individual cell due to biosynthesis processes. But the growth of a multicellular organism is not only an increase in the size of cells, but also their active division - an increase in the number. The growth rate, developmental features, the size to which a certain individual can grow - all this depends on many factors, including the influence of the environment. But the main, determining factor in all these processes is hereditary information, which is stored in the form of chromosomes in the nucleus of each cell. All cells of a multicellular organism originate from a single fertilized egg. In the process of growth, each newly formed cell must receive an exact copy of the genetic material in order, having a common hereditary program of the organism, to specialize and, performing its specific function, be an integral part of the whole.

In connection with differentiation, i.e., division into different types, the cells of a multicellular organism have an unequal life span. For example, nerve cells stop dividing even during fetal development, and during the life of the organism their number can only decrease. Once having arisen, they no longer divide and live as long as the tissue or organ of which they are part, the cells that form striated muscle tissues in animals and storage tissues in plants. Red bone marrow cells are constantly dividing to form blood cells, which have a limited lifespan. In the process of performing their functions, the cells of the skin epithelium quickly die, therefore, in the growth zone of the epidermis, the cells divide very intensively. Cambial cells and growth cone cells in plants are actively dividing. The higher the specialization of cells, the lower their ability to reproduce.

There are about 10 14 cells in the human body. About 70 billion cells of the intestinal epithelium and 2 billion erythrocytes die every day. The shortest-lived cells are the intestinal epithelium, whose lifespan is only 1-2 days.

The life cycle of a cell.

The period of life of a cell from the moment of its appearance in the process of division to death or the end of subsequent division called life cycle . The cell arises in the process of division of the mother cell and disappears during its own division or death. The duration of the life cycle in different cells varies greatly and depends on the type of cells and environmental conditions (temperature, availability of oxygen and nutrients). For example, the life cycle of an amoeba is 36 hours, and bacteria can divide every 20 minutes.

The life cycle of any cell is a set of events that take place in the cell from the moment it arises as a result of division and until death or subsequent death. mitosis. The life cycle may include a mitotic cycle consisting of preparation for mitosis − interphase and the division itself, as well as the stage of specialization - differentiation, during which the cell performs its specific functions. The duration of interphase is always longer than the division itself. In the cells of the intestinal epithelium of rodents, the interphase lasts an average of 15 hours, and division takes place in 0.5–1 hour. During interphase, biosynthesis processes are actively going on in the cell, the cell grows, forms organelles and prepares for the next division. But, undoubtedly, the most important process that occurs during interphase in preparation for division is DNA duplication ().

The two helices of the DNA molecule diverge and a new polynucleotide chain is synthesized on each of them. DNA reduplication occurs with the highest precision, which is ensured by the principle of complementarity. New DNA molecules are absolutely identical copies of the original, and after the duplication process is completed, they remain connected in the centromere region. The DNA molecules that make up chromosomes after reduplication is called chromatids.

There is a deep biological meaning in the exactness of the reduplication process: a violation of copying would lead to a distortion of hereditary information and, as a result, to a disruption in the functioning of daughter cells and the whole organism as a whole.

If DNA duplication did not occur, then with each cell division, the number of chromosomes would be halved and pretty soon there would be no chromosomes left in each cell at all. However, we know that in all cells of the body of a multicellular organism, the number of chromosomes is the same and does not change from generation to generation. This constancy is achieved through mitotic cell division.

Mitosis. Division, during which there is a strictly identical distribution of exactly copied chromosomes between daughter cells, which ensures the formation of genetically identical - the same - cells, is called mitosis.

Cell division. Mitosis" class="img-responsive img-thumbnail">

Rice. 57. Phases of mitosis

The whole process of mitotic division is conditionally divided into four phases of different duration: prophase, metaphase, anaphase and telophase (Fig. 57).

AT prophase chromosomes begin to actively spiralize - twist and acquire a compact shape. As a result of such packaging, reading information from DNA becomes impossible and RNA synthesis stops. Chromosome spiralization is a prerequisite for the successful separation of genetic material between daughter cells. Imagine some small room, the entire volume of which is filled with 46 threads, the total length of which is hundreds of thousands of times greater than the size of this room. This is the nucleus of the human cell. In the process of reduplication, each chromosome doubles, and we already have 92 entangled strands in the same volume. It is almost impossible to divide them equally without getting confused and without tearing. But wind these threads into balls, and you can easily distribute them into two equal groups - 46 balls in each. Something similar happens during mitotic division.

By the end of prophase, the nuclear membrane breaks up, and the spindle fibers are stretched between the poles of the cell - an apparatus that ensures an even distribution of chromosomes.

AT metaphase spiralization of chromosomes becomes maximum, and compact chromosomes are located in the equatorial plane of the cell. At this stage, it is clearly seen that each chromosome consists of two sister chromatids connected at the centromere. The spindle fibers are attached to the centromere.

Anaphase flows very quickly. The centromeres split in two, and from that moment the sister chromatids become independent chromosomes. The spindle fibers attached to the centromeres pull the chromosomes to the poles of the cell.

On the stage telophase daughter chromosomes, gathered at the poles of the cell, unwind and stretch. They again turn into chromatin and become poorly distinguishable in a light microscope. New nuclear membranes form around the chromosomes at both poles of the cell. Two nuclei are formed containing the same diploid sets of chromosomes.

Rice. 58. Division of the cytoplasm in animal (A) and plant (B) cells

Mitosis ends with the division of the cytoplasm. Simultaneously with the divergence of chromosomes, the organelles of the cell are approximately evenly distributed along the two poles. In animal cells, the cell membrane begins to bulge inward, and the cell divides by constriction (Fig. 58). In plant cells, the membrane is formed inside the cell in the equatorial plane and, spreading to the periphery, divides the cell into two equal parts.

Meaning of mitosis. As a result of mitosis, two daughter cells arise, containing the same number of chromosomes as there were in the nucleus of the mother cell, i.e., cells identical to the parent cell are formed. Under normal conditions, no changes in genetic information occur during mitosis, so mitotic division maintains genetic stability cells. Mitosis underlies the growth, development, and vegetative reproduction of multicellular organisms. Thanks to mitosis, the processes of regeneration and replacement of dying cells are carried out (Fig. 59). In unicellular eukaryotes, mitosis ensures asexual reproduction.

Rice. 59. Significance of mitosis: A - growth (root tip); B - vegetative propagation (budding of yeast); B - regeneration (lizard tail)

Review questions and assignments

1. What is the cell life cycle?

2. How does DNA duplication occur in the mitotic cycle? Explain what is the biological meaning of this process.

3. What is the preparation of a cell for mitosis?

4. Describe sequentially the phases of mitosis.

5. Draw a diagram illustrating the biological significance of mitosis.

Think! Execute!

1. Explain why the completion of mitosis - the division of the cytoplasm - occurs differently in animal and plant cells.

2. Cells of what plant tissues actively divide and give rise to all other plant tissues?

Work with computer

Refer to the electronic application. Study the material and complete the assignments.

Interphase. The stage in which a cell prepares for division is called interphase It is divided into several periods.

Presynthetic period(G1) is the longest period of the cell cycle after cell division (mitosis). Number of chromosomes and DNA content - 2 n 2With. In different types of cells, the G1 period can last from several hours to several days. During this period, proteins, nucleotides and all types of RNA are actively synthesized in the cell, mitochondria and proplastids (in plants) are divided, ribosomes and all single-membrane organelles are formed, the cell volume increases, energy accumulates, preparations are underway for DNA reduplication.

Synthetic period(S) is the most important period in the life of a cell, during which DNA duplication (reduplication) occurs. The duration of the S-period is from 6 to 10 hours. At the same time, there is an active synthesis of histone proteins that make up the chromosomes, and their migration to the nucleus. By the end of the period, each chromosome consists of two sister chromatids connected to each other at the centromere. Thus, the number of chromosomes does not change (2 n), and the amount of DNA doubles (4 With).

Postsynthetic period(G2) occurs after completion of chromosome duplication. This is the period of preparation of the cell for division. It lasts 2-6 hours. At this time, energy is actively accumulated for the upcoming division, microtubule proteins (tubulins) and regulatory proteins that trigger mitosis are synthesized.

forms of mitosis. In nature, there are several variants of mitotic cell division.

symmetrical mitosis. The most common form of mitosis in nature, which results in two identical cells.

asymmetric mitosis. Mitosis, in which there is an uneven distribution of the cytoplasm between daughter cells or an uneven distribution of special proteins - differentiation factors that determine the further fate of the cell after division.

Closed mitosis . In some ciliates, algae, and fungi, mitosis proceeds without destruction of the nuclear envelope. In this case, the fission spindle can be located inside a special channel that is formed in the nucleus. The molecular mechanisms of closed mitosis are still not well understood.

Amitosis. Amitosis, or direct division, - cell division without the formation of a division spindle. The interphase nucleus is divided by constriction into two parts. In this case, there is no uniform distribution of genetic material between two daughter cells. Most often, amitosis occurs in cells of highly specialized tissues that no longer need to divide further, during aging, tissue degeneration, and in malignant tumor cells.

It should be noted that at present, most scientists believe that all phenomena attributed to amitosis are descriptions of certain pathological processes or the result of an incorrect interpretation of insufficiently prepared micropreparations. However, some variants of nuclear division in eukaryotic cells cannot be attributed to either mitosis or meiosis. Such, for example, is the division of the macronuclei of many ciliates, which occurs without the formation of a fission spindle.

Plants

Educational fabrics. Cells of specialized plant tissues (integumentary, mechanical, conductive) are not capable of division. Therefore, there must be tissues in the plant whose only function is to form new cells. Only on them depends the possibility of plant growth. These are educational tissues, or meristems (from the Greek. meristos- divisible).

Educational tissues, or meristems, consist of small thin-walled large-nuclear cells containing proplastids, mitochondria and small vacuoles that are practically indistinguishable under a light microscope. Meristems provide plant growth and the formation of all other types of tissues. Their cells divide by mitosis. After each division, one of the sister cells retains the properties of the mother cell, while the other soon stops dividing and proceeds to the initial stages of differentiation, subsequently forming cells of a certain tissue.

Educational tissues in the body of a plant are located in different places, and therefore they are divided into several groups.

Apical (apical) meristems. They are located on the tops of the axial organs - the stem and root, ensuring the growth of these organs in length. As branching occurs, each new lateral shoot or root develops its own apical meristems.

Side (lateral) meristems. Provide thickening of axial organs. This is the cambium, characteristic of gymnosperms and dicotyledonous plants, and the phellogen, which forms the integumentary tissue - cork, or fellema.

Insertion (intercalary) meristems. They are located in the lower part of the internode of the stem of cereals and at the base of young leaves, providing the growth of these organs. As the growth of the leaf or stem section ends, the intercalary meristem turns into permanent tissues.

One of the most important processes in the individual development of a living organism is mitosis. In this article, we will briefly and clearly try to explain what processes occur during cell division, and talk about the biological significance of mitosis.

Concept definition

From biology textbooks for grade 10, we know that mitosis is cell division, as a result of which two daughter cells with the same set of chromosomes are formed from one mother cell.

Translated from the ancient Greek language, the term "mitosis" means "thread". It is like a link between old and new cells, in which the genetic code is stored.

The process of division as a whole starts from the nucleus and ends with the cytoplasm. It is referred to as the mitotic cycle, which consists of the stage of mitosis and interphase. As a result of division of a diploid somatic cell, two daughter cells are formed. Due to this process, an increase in the number of tissue cells occurs.

Stages of mitosis

Based on morphological features, the division process is divided into the following stages:

• Prophase ;

At this stage, the nucleus condenses, chromatin condenses inside it, which twists into a spiral, chromosomes are viewed under a microscope.

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Under the influence of enzymes, the nuclei and their membranes dissolve, the chromosomes in this period are randomly arranged in the cytoplasm. Later, the separation of centrioles to the poles occurs, a spindle of cell division is formed, the threads of which are attached to the poles and chromosomes.

This stage is characterized by DNA doubling, but pairs of chromosomes still hold on to each other.

Before the prophase stage, the plant cell has a preparatory phase - preprophase. What is the preparation of the cell for mitosis can be understood at this stage. It is characterized by the formation of a preprophase ring, phragmosomes, and the nucleation of microtubules around the nucleus.

• prometaphase ;

At this stage, the chromosomes begin to move and head towards the nearest pole.

In many textbooks, preprophase and prometophase are referred to as the prophase stage.

• metaphase ;

At the initial stage, the chromosomes are located in the equatorial part of the spindle, so that the pressure of the poles acts on them evenly. During this stage, the number of spindle microtubules is constantly growing and being renewed.

The chromosomes line up in pairs in a spiral along the equator of the spindle in a strict order. Chromatids gradually detach, but still hold on to the spindle threads.

• Anaphase ;

At this stage, elongation of the chromatids occurs, which gradually diverge towards the poles, as the spindle threads contract. Daughter chromosomes are formed.

In terms of time, this is the shortest phase. Sister chromatids suddenly separate and move to different poles.

• Telophase ;

It is the last phase of division when the chromosomes lengthen and a new nuclear envelope is formed near each pole. The threads that made up the spindle are completely destroyed. During this stage, the cytoplasm divides.

The completion of the last stage coincides with the division of the mother cell, which is called cytokinesis. It depends on the passage of this process how many cells are formed during division, there can be two or more.

Rice. 1. Stages of mitosis

Meaning of Mitosis

The biological significance of the process of cell division is undeniable.

• It is thanks to him that it is possible to maintain a constant set of chromosomes.
• Reproduction of an identical cell is possible only by mitosis. In this way, skin cells, intestinal epithelium, red blood cells, the life cycle of which is only 4 months, are replaced.
• Copying, and hence the preservation of genetic information.
• Ensuring the development and growth of cells, due to which a multicellular organism is formed from a single-celled zygote.
• With the help of such a division, the regeneration of body parts is possible in some living organisms. For example, the rays of a starfish are restored.

Rice. 2. Starfish regeneration

• Ensuring asexual reproduction. For example, hydra budding, as well as vegetative propagation of plants.

Rice. 3. Hydra Budding

What have we learned?

Cell division is called mitosis. Thanks to him, the genetic information of the cell is copied and stored. The process occurs in several stages: preparatory phase, prophase, metaphase, anaphase, telophase. As a result, two daughter cells are formed, which are completely similar to the original mother cell. In nature, the significance of mitosis is great, since it makes possible the development and growth of unicellular and multicellular organisms, the regeneration of certain parts of the body, and asexual reproduction.

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Cell life cycle

Patterns of cell existence in time

The ability of a cell to reproduce is one of the fundamental properties of living things. Cell division underlies embryogenesis and regeneration.

Regular changes in the structural and functional characteristics of the cell over time constitute the content cell life cycle (cell cycle). The cell cycle is the period of existence of a cell from the moment of its formation by dividing the mother cell to its own division or death.

An important component of the cell cycle is mitotic (proliferative) cycle- a complex of interrelated and coordinated in time events occurring in the process of preparing a cell for division and during the division itself. In addition, the life cycle includes cell execution period multicellular organism specific functions as well as dormant periods. During periods of rest, the immediate fate of the cell is not determined: it can either begin preparation for mitosis, or begin specialization in a certain functional direction.

The duration of the mitotic cycle for most cells is from 10 to 50 hours. Its value varies significantly: for bacteria it is 20-30 minutes, for a shoe 1-2 times a day, for an amoeba about 1.5 days. The duration of the cycle is regulated by changing the duration of all its periods. Multicellular cells also have a different ability to divide. In early embryogenesis, they divide frequently, and in the adult organism, for the most part, they lose this ability, as they become specialized. But even in an organism that has reached full development, many cells must divide to replace worn-out cells that are constantly shedding and, finally, new cells are needed to heal wounds.

Therefore, in some populations of cells, division must occur throughout life. Given this, all cells can be divided into three categories:

1. In the body of higher vertebrates, not all cells are constantly dividing. There are specialized cells that have lost the ability to divide (neutrophils, basophils, eosinophils, nerve cells). By the time of the birth of a child, nerve cells reach a highly specialized state, losing the ability to divide. In the process of ontogenesis, their number continuously decreases. This circumstance has one good side; if the nerve cells were dividing, then the higher nervous functions (memory, thinking) would be disrupted.

2. Another category of cells is also highly specialized, but due to their constant desquamation, they are replaced by new ones, and this function is performed by cells of the same line, but not yet specialized and have not lost the ability to divide. These cells are called renewing. An example is the constantly renewing cells of the intestinal epithelium, hematopoietic cells. Even bone tissue cells can form from non-specialized ones (this can be observed during reparative regeneration of bone fractures). Populations of unspecialized cells that retain the ability to divide are usually called stem cells.

3. The third category of cells is an exception, when highly specialized cells under certain conditions can enter the mitotic cycle. We are talking about cells that are characterized by a long lifespan and where, after complete growth, cell division rarely occurs. An example is hepatocytes. But if 2/3 of the liver is removed from an experimental animal, then in less than two weeks it is restored to its previous size. So are the cells of the glands that produce hormones: under normal conditions, only a few of them are able to reproduce, and under altered conditions, most of them can begin to divide.

According to the two main events of the mitotic cycle, it is distinguished reproductive and dividing phases corresponding interphase and mitosis classical cytology.

In the initial segment of interphase (in eukaryotes 8-10 hours) (postmitotic, presynthetic, or G 1 period) the features of the organization of the interphase cell are restored, the formation of the nucleolus, which began in the telophase, is completed. A significant (up to 90%) amount of protein enters the nucleus from the cytoplasm. In the cytoplasm, parallel to the reorganization of the ultrastructure, protein synthesis is intensified. This contributes to the growth of cell mass. If the daughter cell has to enter the next mitotic cycle, the syntheses become directed: chemical precursors of DNA are formed, enzymes that catalyze the DNA reduplication reaction, and a protein is synthesized that starts this reaction. Thus, the processes of preparing the next period of the interphase - the synthetic one - are carried out. Cells have a diploid set of chromosomes 2n and 2c genetic material DNA (the genetic formula of a cell).

AT synthetic or S-period (6-10 h) the amount of hereditary material of the cell doubles. With few exceptions reduplication(sometimes DNA duplication is referred to by the term replication, leaving the term reduplication to denote doubling of chromosomes.) DNA is carried out in a semi-conservative way. It consists in the divergence of the DNA helix into two chains, followed by the synthesis of a complementary chain near each of them. The result is two identical coils. DNA molecules that are complementary to maternal ones are formed in separate fragments along the length of the chromosome, moreover, non-simultaneously (asynchronously) in different parts of the same chromosome, as well as in different chromosomes. Then parcels (replication units - replicons) of the newly formed DNA are “crosslinked” into one macromolecule. There are over 50,000 replicons in a human cell. The length of each of them is about 30 µm. Their number changes in ontogeny. The meaning of DNA replication by replicons becomes clear from the following comparisons. The rate of DNA synthesis is 0.5 µm/min. In this case, the reduplication of a DNA strand of one human chromosome about 7 cm long would have to take about three months. The regions of chromosomes where synthesis begins are called initiation points. Perhaps they are the sites of attachment of interphase chromosomes to the inner membrane of the nuclear envelope. It can be assumed that the DNA of individual fractions, which will be discussed below, is replicated in a strictly defined phase of the S-period. Thus, most of the rRNA genes double the DNA at the beginning of the period. Reduplication is triggered by a signal entering the nucleus from the cytoplasm, the nature of which is not clear. DNA synthesis in the replicon is preceded by RNA synthesis. In a cell that has passed the S-period of interphase, the chromosomes contain a double amount of genetic material. Along with DNA, RNA and protein are intensively formed in the synthetic period, and the number of histones is strictly doubled.

Approximately 1% of the DNA of an animal cell is located in the mitochondria. An insignificant part of mitochondrial DNA is replicated in the synthetic period, while the main part is replicated in the postsynthetic period of the interphase. At the same time, it is known that the lifespan of mitochondria in liver cells, for example, is 10 days. Considering that hepatocytes rarely divide under normal conditions, it should be assumed that mitochondrial DNA reduplication can occur regardless of the stages of the mitotic cycle. Each chromosome is made up of two sister chromatids ( 2n), contains DNA 4c.

The time interval from the end of the synthetic period to the beginning of mitosis takes postsynthetic (pre-mitotic), or G 2 - period interphase ( 2n and 4c) (3-6 hours). It is characterized by intensive synthesis of RNA and especially protein. The doubling of the mass of the cytoplasm is completed in comparison with the beginning of the interphase. This is necessary for the cell to enter mitosis. Part of the formed proteins (tubulins) is used later to build spindle microtubules. Synthetic and postsynthetic periods are directly related to mitosis. This allows you to highlight them in a special period of interphase - preprophase.

Exist three types of cell division: mitosis, amitosis, meiosis.