Mitosis, cell cycle. Mitosis and meiosis Comparative analysis

“Biology Cell Structure” - Diffusion. Find out the mechanisms of transport of substances across the cell membrane. Topic of the educational project: Structural organization of the cell. Problematic issues of the topic: Abstract of the project. Features of plant, animal, fungal cells. Learn to use different sources of information. Integration of the project with the educational topic “Fundamentals of molecular kinetic theory.

“Structure of a prokaryotic cell” - Make a cluster. Sporulation. Respiration of bacteria. What is the significance of bacteria. Features of bacterial nutrition. Comparison of prokaryotic and eukaryotic cells. Testing and updating knowledge. Water. Consolidation of knowledge. Look carefully at the drawings. Anthony van Leeuwenhoek. Reproduction. When did prokaryotic organisms arise?

“Cytoplasm” - Maintains the turgor (volume) of the cell, maintaining temperature. EPS functions. Glycolysis and the synthesis of fatty acids, nucleotides and other substances occur in the cytosol. Endoplasmic reticulum. Chemical composition The cytoplasm is diverse. Cytoplasm. Halioplasm/cytosol. The structure of an animal cell. Alkaline reaction.

“The cell and its structure” - A – phases and periods of muscle contraction, B – modes of muscle contraction that occur at different frequencies of muscle stimulation. Pattern of movements in the muscle myofibril. The change in muscle length is shown in blue, the action potential in the muscle is shown in red, and the excitability of the muscle is shown in purple. Transmission of excitation in an electrical synapse.

“Structure of a cell, grade 6” - I. Structure of a plant cell. - Support and protection of the body. - Energy and water reserves in the body. How did the water in the glass change after adding iodine? - Storage and transfer of inheritance. Transparent. Laboratory work. 1. Proteins. Meaning. - Transfer of substances, movement, protection of the body. Substance. 3. Fats. Organic substances of the cell.

Contents Types of reproduction…………… 3 Mitosis……………………. 5 Amitosis…………………. . 16 Sexual reproduction…………………. 18 Meiosis……………………… 20 Gametogenesis……………… 26 Types and structure of gametes………………… 28 Alternation of generations………………. 29 Parthenogenesis……………….

Reproduction is the reproduction of one’s own kind, ensuring continuity and continuity of life. This is one of the most important properties of living organisms. Thanks to reproduction, the following occurs: 1. Transfer of hereditary information. 2. Continuity of generations is preserved. 3. The duration of existence of the species is maintained. 4. The number of the species increases and the territory (area) of residence expands. Reproduction is based on cell division, which ensures an increase in the number of cells and the growth of a multicellular organism.

TYPES OF REPRODUCTION Reproduction Asexual Sexual Actually asexual (by one cell) Vegetative (by a group of cells) Conjugation (unicellular organisms) Multicellular organisms Without fertilization With fertilization

Asexual reproduction Actually asexual reproduction (by one cell): : 1. Fission in two (simple) 2. Mitosis 3. Amitosis 4. Budding 5. Sporulation Vegetative reproduction (by a group of cells) : : 1. Budding 2. Fragmentation 3. Vegetative propagation of plants

MITOSIS, OR INDIRECT DIVISION Mitosis ((Latin Mitos - thread) is a division of the cell nucleus in which two daughter nuclei are formed with a set of chromosomes identical to the parent cell. Mitosis = division of the nucleus + division of the cytoplasm For the first time, mitosis in plants was observed by I. D. Chis-tyakov in 1874, and the process was described in detail by the German botanist E. Strasburger (1877) and the German zoologist W. Fleming (1882).

Cell cycle The period of a cell's existence from one division to another is called the mitotic, or cell cycle. The cell cycle in plants lasts from 10 to 30 hours. Nuclear division (mitosis) takes about 10% of this time. P 1 - presynthetic period C - synthetic period P 2 - postsynthetic period

The structure of chromosomes at different periods of the cell cycle 1 2 3 4 1, 2 – pre-synthetic period; 3 – synthetic and postsynthetic period; 4 – metaphase. 1. During the presynthetic period, the cell grows: protein and RNA are synthesized and the amount of organic substances increases. 2. During the synthetic period, DNA replication (doubling) occurs. From this point on, each chromosome consists of two chromatids. 3. During the post-synthesis period, there is intensive synthesis of protein and ATP, necessary for cell division.

Sections of chromatin in the interphase nucleus 1. DNA strand in the form of chromatin. 2. It is in the form of a chromosome during cell division

PROPHASE Chromatin spirals into bichromatid chromosomes; the nuclear envelope and nucleolus dissolve; Centrioles diverge towards the poles; (2 n 4 c).

METAPHASE Bichromatid chromosomes line up at the equator of the cell; Centrioles form spindle threads, which are attached to the centromeres of chromosomes; (2 n 4 c).

ANAPHASE When the spindle strands contract, the centromeres of the chromosomes divide and the chromatids of each chromosome move to the poles of the cell; (4 n 4 c). Each chromatid is considered an independent chromosome

TELOPHASE Single-chromatid (daughter) chromosomes unwind, a nucleolus is formed and a nuclear envelope is formed around them; a partition begins to form at the equator; in nuclei 2 n 2 c.

CYTOKINESIS (cytoplasmic division) Formation of a double-membrane septum along the equator of the cell, followed by complete separation of daughter cells. In plants, a cell wall is formed along the equator of the cell. Cell cytokinesis (photo)

The set of chromosomes (number, shape and size) in a somatic cell is called a karyotype. The karyotype contains a double ((diploid) set of chromosomes (2 n 2 n),), constant for each type of organism. Diploid set of human chromosomes

SIGNIFICANCE OF MITOSIS 1. Leads to an increase in the number of cells and ensures the growth of a multicellular organism. 2. Provides replacement for worn or damaged tissue. 3. Maintains the set of chromosomes in all somatic cells. 4. Serves as a mechanism for asexual reproduction, which creates offspring that are genetically identical to the parents. 5. Allows you to study the karyotype of the organism (in metaphase).

Amitosis or direct division Amitosis is the division of the interphase nucleus by constriction without the formation of a fission spindle. Prevalence in nature: Normal 1. Amoeba 2. Large nucleus of ciliates 3. Endosperm 4. Potato tuber 5. Cornea 6. Cartilage and liver cells Pathology 1. Inflammation 2. Malignant neoplasms Meaning: economical (low energy consumption) process of cell reproduction

SCHIZOGONY Schizogony (gr. schizo – split) – multiple asexual reproduction in sporozoans, foraminifera and some algae. The cell nucleus (schizont) is divided by rapidly successive divisions into several nuclei, and the entire cell then breaks up into the corresponding number of mononuclear cells—merozoites. .

SEXUAL REPRODUCTION Sexual reproduction has an advantage over asexual reproduction, since two parents take part. ♂ ♂ sperm ((n)n) + ♀ egg (n)(n) = = zygote (2(2 n)n) The zygote carries the hereditary characteristics of both parents, which significantly increases the hereditary variability of the offspring and increases their ability to adapt to environmental conditions Sexual reproduction is associated with the formation in the genital organs (gonads) of specialized cells - gametes, which are formed as a result of a special type of cell division - meiosis.

Meiosis is indirect cell division; the process of cell division in which the number of chromosomes in a cell is halved. (reduction) As a result of this division, haploid (n) germ cells (gametes) and spores are formed. MEIOSIS ZYGOTIC GAMET SPOROUS In the zygote after fertilization, which leads to the formation of zoospores in algae and mycelium of fungi. In the genital organs, leads to the formation of gametes In seed plants, leads to the formation of a haploid gametophyte

MEIOSIS Meiosis consists of two successive divisions - meiosis 1 and meiosis 2. DNA duplication occurs only before meiosis 1, and there is no interphase between divisions. During the first division, homologous chromosomes diverge and their number is halved, and in the second division, chromatids separate and mature gametes are formed. A feature of the first division is the complex and time-consuming prophase.

PROPHASE 1 (2 n 4 s) Prophase 1 is the longest 2 n 4 s Spiralization of chromatin into bichromatid chromosomes; Centrioles diverge towards the poles; bringing together (conjugation) and shortening of homologous chromosomes with subsequent crossing and exchange of homologous regions (crossing over); dissolution of the nuclear membrane.

METAPHASE 1 (2 n 4 c) Homologous chromosomes are located in pairs at the equator and repel each other. A fission spindle is formed. The spindle strands are attached to the bichromatid chromosomes.

ANAPHASE 1 (2 n 4 c) Homologous chromosomes, consisting of two chromatids, diverge to the poles. There is a decrease (reduction) of chromosomes at the poles of the cell.

TELOPHASE 1 (1 n 2 c) In telophase, from each pair of homologous chromosomes, one appears in the daughter cells, and the chromosome set becomes haploid. However, each chromosome consists of two chromatids, so the cell immediately begins the second division.

MEIOSIS 2 (1 n 2 c, 1, 1 nn 2 c, 2 n 2 c, nc)nc) The second meiotic division occurs according to the type of mitosis. In anaphase 2, chromatids move toward the poles, which become daughter chromosomes. From each initial cell, as a result of meiosis, four cells with a haploid set of chromosomes are formed.

GAMETOGENESIS GAMETOGENESIS Spermatogenesis ♂♂ Oogenesis ♀♀ (in the testes) (in the ovaries) Reproduction period (mitosis) In the reproductive period In the embryonic period Growth period (interphase) Insignificant Long period Spermocyte of the 1st order Oocyte of the 1st order Maturation period (meiosis) First and second First and second meiotic uneven division meiotic division 4 sperm 1 egg

Development of gametes in flowering plants Development of pollen grains. Each pollen grain develops from a microspore mother cell, which undergoes meiosis to produce 4 pollen grains. Development of the embryonic grain. The embryo sac develops from a haploid megaspore resulting from meiotic division of the macrospore mother cell.

Types and structure of gametes 1 2 Fig. 1. Spermatozoa: 1 - rabbit, 2 - rat, 3 - guinea pig, 4 - human, 5 - crayfish, 6 - spider, 7 - beetle, 8 - horsetail, 9 - moss, 1 O - fern. Rice. 2. Mammalian egg: 1 – shell, 2 – nucleus, 3 – cytoplasm, 4 – follicular cells. The terms sperm and egg were coined by Karl Baer in 1827.

Even if offspring receive identical genes from both parents, the effect of these genes may be different, since genes carry a parental “imprint” that is different in males and females, which affects the normal development of the body and also plays a role in the occurrence of diseases. The phenomenon when, during the formation of gametes in a descendant, the previous chromosomal “imprint” received from the parents is erased and its genes are marked in accordance with the sex of a given individual, is called genomic imprinting

Varied life cycles(alternation of generations)) A – zygotic meiosis: green algae, mushrooms. B – gametic meiosis: vertebrates, mollusks, arthropods. B – spore meiosis: brown, red algae and all higher plants.

The significance of meiosis The number of chromosomes is maintained from generation to generation. Mature gametes receive a haploid number (n) of chromosomes, and upon fertilization, the diploid number of chromosomes characteristic of a given species is restored. A large number of new gene combinations are formed during crossing over and fusion of gametes (combinative variability), which gives new material for evolution (offspring differ from parents). ♂ (n) + ♀ (n) = zygote (2 n) → new organism (2 n)

Parthenogenesis (gr. virgin origin) is sexual reproduction in which the development of a new organism occurs from an unfertilized egg. Parthenogenesis Facultative Cyclic Obligatory (obligate) Both without fertilization and after it: bees, ants, rotifers ♂ + ♀ = females ♀ → males Arose as a way to regulate the sex ratio In Daphnia, aphids ♀ → ♀ - in summer ♂ + ♀ - in the fall Arose as a method of survival due to the great death of individuals All individuals are females (Caucasian rock lizard) Arose as a method of survival of the species due to the difficulties of individuals meeting each other In plants (cruciferous plants, Asteraceae, Rosaceae, etc.), parthenogenesis is called apomixis.

Control and generalization test 1. At what period of the cell cycle does the amount of DNA double? A) metaphase, b) prophase, c) synthetic period, d) presynthetic period. 2. During what period of mitosis do chromosomes line up along the equator? A) in prophase, b) in metaphase, c) in anaphase, d) in telophase. 3. Which event is missing in mitosis compared to meiosis? A) DNA duplication, b) conjugation and crossing over of chromosomes, c) divergence of chromosomes to the poles. 4. What set of chromosomes is obtained during mitotic division? A) haploid, b) diploid, c) triploid. 5. What is characteristic of the period of fragmentation (blastomeres)? A) meiotic division, b) active cell growth, c) cellular specialization, d) mitotic division. 6. How does the fertilization process end? A) the approach of the sperm to the egg, b) the penetration of the sperm into the egg, c) the fusion of nuclei and the formation of a zygote. 7. Nervous system develops from: a) endoderm, b) mesoderm, c) ectoderm.

8. How many chromatids are in a chromosome at the end of mitosis? A)1, b)2, c)3, d)4. 9. Embryo at the gastrula stage: a) single-layer, b) two-layer, c) multi-layer. 10. If bees have a diploid set of chromosomes equal to 32, then the following have 16 chromosomes: a) drone, b) queen, c) worker bee. 11. What is the set of chromosomes in the endosperm of a wheat grain? A) haploid, b) diploid, c) triploid. 12. What happens during the postsynthetic stage of interphase? A) cell growth and synthesis of organic substances, b) DNA doubling, c) accumulation of ATP. 13. What division underlies sexual reproduction? A) mitosis, b) amitosis, c) meiosis, d) schizogony. 14. What is formed as a result of oogenesis? A) sperm, b) egg, c) zygote, d) body cells. 15. What set of chromosomes will be in the cell after meiotic division if the mother had 12? 16. From which germ layer do muscles form?

Standard answers to control test 1. c; 2. b; 3. b; 4. b; 5. g; 6. in; 7. in; 8. a; 9. in; 10. a; 11. in; 12. in; 13. in; 14. b. 15. 6 chromosomes, 20. From mesoderm;

Proteins on scattering chromosomes help rebuild cytoskeletal reinforcements to make it easier for the cell to divide.

Cell division: on the left - chromosomes lined up at the cell equator, in the middle - divergence of chromosomes, on the right - chromosomes diverged to the poles of division. Chromosomal DNA is colored blue, microtubules are colored red. (Photo by Wellcome Images/Flickr.com)

We all remember pictures of a dividing cell from a biology textbook: the nuclear membrane disappears, the chromosomes line up at the equator of the cell, and then scatter to opposite poles - all that remains is to pull the parent cell in two or build a cell wall. The scattering of chromosomes, as again written in any textbook, occurs due to the work of protein microtubules attached to special protein complexes on chromosomes - kinetochores.

However, despite the fact that cell division has been studied far and wide, exciting details are still being revealed to us here, hitherto unknown. For a long time, it was thought that chromosomes in a dividing cell are simply a passive load, that they move where they are dragged by the complex molecular apparatus of spindle microtubules. But this, as researchers from the University of Montreal and University College London have found, is not entirely true. Experimenting with Drosophila and human cells, Buzz Baum ( Buzz Baum) together with colleagues Nelio Rodriguez ( Nelio T. L. Rodrigues), Sergei Lekomtsev and others found out that chromosomes can influence the functioning of the protein “ropes” that drag them to the pole of the cell.

As mentioned above, microtubules-“ropes” hold on to kinetochores - a special protein complex on the chromosome. Among the kinetochore proteins, it was possible to find the enzyme PP1–Sds22 (PP1 phosphatase and its regulatory subunit Sds22), which acted on cytoskeletal proteins located near the cell membrane at the division poles, that is, where chromosomes were attracted. The poles begin to pull in opposite directions from each other soon after the chromosomes begin to separate.

The extension of the poles further helps separate the chromosomes and facilitates cell division. But underneath the cell membrane there is a cytoskeletal substrate that adds strength and elasticity to the membrane. In order for the poles to begin to diverge, the cytoskeletal “fasteners” must be weakened. This is exactly what the aforementioned enzyme sitting on the chromosomes does - it begins to work after the chromosomes begin to move towards the poles.

Cells of multicellular organisms usually have a double, or diploid (2 n), set of chromosomes, since the zygote (the egg from which the organism develops) as a result of fertilization receives one set of chromosomes from each parent. Therefore, all the chromosomes of the set are paired, homologous - one from the father, the other from the mother. In cells, this set is maintained constant through mitosis.

Sex cells (gametes) - eggs and sperm (or sperm in plants) - have a single, or haploid, set of chromosomes (n). This set of gametes is obtained through meiosis (from the Greek word meiosis - reduction). During the process of meiosis, one chromosome doubling and two divisions occur - reduction and equational (equal). Each of them consists of a number of phases: interphase, prophase, metaphase, anaphase and telophase (Fig. 1).

In interphase I (first division), doubling - reduplication - of chromosomes occurs. Each chromosome then consists of two identical chromatids connected by a single centromere. In prophase I of meiosis, pairing (conjugation) of doubled homologous chromosomes occurs, which form bivalents consisting of four chromatids. At this time, spiralization, shortening and thickening of chromosomes occurs. In metaphase I, paired homologous chromosomes line up at the equator of the cell, in anaphase I they diverge to its different poles, and in telophase I the cell divides. After the first division, only one doubled chromosome from each pair of homologous chromosomes enters each of the two cells, i.e., the number of chromosomes is halved.

After the first division, the cells undergo a short interphase II (second division) without chromosome doubling. The second division occurs as mitosis. In metaphase II, chromosomes, consisting of two chromatids, line up at the equator of the cell. In anaphase II, chromatids move toward the poles. In telophase II, both cells divide. It has been established that there is a direct relationship between the set of chromosomes in the nucleus (2 n or n) and the amount of DNA in it (denoted by the letter C). A diploid cell has twice as much DNA (2C) as a haploid cell (C). In interphase I of a diploid cell, before preparing it for division, DNA replication occurs, its amount doubles and becomes equal to 4C. After the first division, the amount of DNA in the daughter cells decreases to 2C, after the second division - to 1C, which corresponds to the haploid set of chromosomes.

The biological meaning of meiosis is as follows. First of all, over a number of generations, the set of chromosomes characteristic of a given species is preserved, since during fertilization, haploid gametes merge and the diploid set of chromosomes is restored.

In addition, in meiosis, processes occur that ensure the implementation of the basic laws of heredity: firstly, thanks to conjugation and the obligatory subsequent divergence of homologous chromosomes, the law of gamete purity is implemented - each gamete receives only one chromosome from a pair of homologues and, therefore, only one allele from a pair - A or a, B or b.

Secondly, the random divergence of non-homologous chromosomes in the first division ensures independent inheritance of traits controlled by genes located on different chromosomes and leads to the formation of new combinations of chromosomes and genes (Fig. 2).

Third, genes located on the same chromosome exhibit linked inheritance. However, they can combine and form new combinations of genes as a result of crossing over - the exchange of sections between homologous chromosomes, which occurs during their conjugation in the prophase of the first division (Fig. 3).

Thus, two mechanisms for the formation of new combinations (genetic recombination) in meiosis can be distinguished: random divergence of non-homologous chromosomes and crossing over.

Cells of multicellular organisms usually have a double, or diploid (2p), set of chromosomes, since the zygote (the egg from which the organism develops) as a result of fertilization receives one set of chromosomes from each parent. Therefore, all the chromosomes of the set are paired, homologous - one from the father, the other from the mother. In cells, this set is kept constant through mitosis.

Sex cells (gametes) - eggs and sperm (or sperm in plants) - have a single, or haploid, set of chromosomes (p). This set of gametes is obtained through meiosis (from the Greek word meiosis - reduction). During the process of meiosis, one chromosome doubling and two divisions occur - reduction and equational (equal). Each of them consists of a number of phases: interphase, prophase, metaphase, anaphase and telophase (Fig. 1).

Rice. 1. Scheme of meiosis:
1 - original mother cell (2p, 2s); 2 - in interphase I, doubling (reduplication) of homologous chromosomes occurs (4c). Each chromosome consists of two chromatids; 3 - in prophase I, conjugation (pairing) of homologous chromosomes occurs, the formation of bivalents; 4 - in metaphase I, bivalents line up at the equator of the cell, a division spindle is formed; 5 - in anaphase I, homologous chromosomes diverge to different poles of the cell; 6 - daughter cells after the first division. Each cell has only one of a pair of homologous chromosomes (2c) - reduction in the number of chromosomes; 7 - in metaphase II, chromosomes consisting of two chromatids are lined up at the equator of cells; 8 - in anaphase II, chromatids move to the poles of the cells; 9 - daughter cells after the second division, in each cell the set of chromosomes is halved (p, s).

After the first division, only one doubled chromosome from each pair of homologous chromosomes enters each of the two cells, i.e., the number of chromosomes is halved.

After the first division, the cells undergo a short interphase II (second division) without chromosome doubling. The second division occurs as mitosis. In metaphase II, chromosomes, consisting of two chromatids, line up at the equator of the cell. In anaphase II, chromatids move toward the poles. In telophase II, both cells divide. It has been established that there is a direct relationship between the set of chromosomes in the nucleus (2 p or n) and the amount of DNA in it (denoted by the letter C). A diploid cell has twice as much DNA (2C) as a haploid cell (C). In interphase I of a diploid cell, before preparing it for division, DNA replication occurs, its quantity doubles and the number of DNA in daughter cells decreases to 2C, after the second division - to 1C, which corresponds to the haploid set of chromosomes.

Rice. 2. Genetic recombination with random divergence of non-homologous chromosomes. Implementation of independent inheritance. Since the orientation probabilities of variants I and II are the same, genes A and B are distributed randomly, independently of each other. With equal probability, 4 types of gametes are formed: A B, Av, and B, Av. This ensures, during random fertilization, the independent inheritance of traits controlled by genes located on different chromosomes. The numbers indicate the centromeres of the chromosomes.

Rice. 3. Genetic recombination during meiotic crossing over. The diagram shows that genes C and D are transmitted together (linked) in the same combinations as they were in the parent cells - CD and cd (non-crossover gametes). In some cells in which crossing over took place between genes C and D, new combinations of genes are formed that are different from the parent ones - Cd and cd (crossover gametes).

Thus, two mechanisms for the formation of new combinations (genetic recombination) in meiosis can be distinguished: random divergence of non-homologous chromosomes and crossing over.