Chromosomal set of potato somatic cells 48. Cell life cycle. Chromosomal set of the cell. Cell division. The divergence of chromatids to the poles of the cell occurs in

A selection of materials for task No. 27 on the topic: “The task of cytology” is presented. For successful implementation, you need to know the theory. After reviewing the task execution plan, graduates will accurately represent the technology for performing such tasks. The subject of the task covers the course of the school subject of biology. Here are the tasks for finding errors in the text from part 2

task 27.doc

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Task 27 “Cytology task” “Protein biosynthesis” 1. tRNA anticodons enter the ribosomes in the following nucleotide sequence UCG, CGA, AAU, CCC. Determine the sequence of nucleotides on mRNA, the sequence of nucleotides on DNA encoding a certain protein and the sequence of amino acids in a fragment of a synthesized protein molecule using the genetic code table: Genetic code (mRNA) First base Second base Third base n F e n L e i L e i L e i L e i L e i L e i i l e i i l e i l e i le i le i le m e t w a l t c s er s er s er s er P r o P r o P r o P r o T r e T r e T r e T r e T r e A l a A T i r T i r - - G i s G i s G l n G l n A s n A s n L i z L i z A s p G C i s C i s - T r i A r g A r g A r g A r g S e r S e r A r g A r g G l and U C A G U C A G U C A G U C A U C A G

V a l V a l V a l A la A la A la A with p G l u G u G l and G l and G l and G 2. The sequence of amino acids in a fragment of a protein molecule is as follows: FENGLUMET. Determine, using the table of the genetic code, the possible DNA triplets that encode this protein fragment. 3. It is known that all types of RNA are synthesized on a DNA matrix. The fragment of the DNA molecule on which the tRNA site is synthesized has the following nucleotide sequence TTGGAA AAACGGACT. Set the nucleotide sequence of the tRNA region that is synthesized on this fragment. Which mRNA codon will correspond to the central anticodon of this tRNA? What amino acid will be transported by this tRNA? Explain the answer. To solve the task, use the table of the genetic code. 4. 30 tRNA molecules participated in the translation process. Determine the number of amino acids that make up the synthesized protein, as well as the number of triplets and nucleotides in the gene that encodes this protein. 5. Determine the mRNA nucleotide sequence, tRNA anticodons, and amino acid sequence of the corresponding fragment of the protein molecule (using the genetic code table) if the DNA chain fragment has the following nucleotide sequence: GT ГЦГТСААААА. 6. One of the DNA chains has a nucleotide sequence: CATGGCTGT-TCC-GTC. Explain how the structure of a protein molecule will change if the fourth triplet of nucleotides in the DNA chain is doubled? 7. tRNA molecules with anticodons UGA, AUG, AGU, GHC, AAU are involved in the biosynthesis of the polypeptide. Determine the nucleotide sequence of the section of each chain of the DNA molecule, which carries information about the synthesized polypeptide, and the number of nucleotides containing adenine (A), guanine (G), thymine (T), cytosine (C) in a double-stranded DNA molecule. Explain the answer. 8. tRNAs with anticodons participated in protein biosynthesis: UUA, HGC, CHC, AUU, CGU. Determine the nucleotide sequence of the section of each chain of the DNA molecule that carries information about the synthesized polypeptide, and the number of nucleotides containing adenine, guanine, thymine, cytosine in a double-stranded DNA molecule. 9. Ribosomes from different cells, the entire set of amino acids and the same molecules of mRNA and tRNA were placed in a test tube, and all the conditions for protein synthesis were created. Why will one type of protein be synthesized on different ribosomes in a test tube? 10. Determine: the nucleotide sequence on the mRNA, the anticodons of the corresponding tRNA and the amino acid sequence of the corresponding fragment of the protein molecule (using the table of the genetic code), if the DNA chain fragment has the following nucleotide sequence: GTGTATGGAAGT. 11. A fragment of the DNA chain has the following nucleotide sequence: TACCTCCACCTG. Determine the nucleotide sequence on mRNA, anticodons of the corresponding tRNA and am

the nocidic sequence of the corresponding fragment of the protein molecule using the table of the genetic code. 12. A fragment of a DNA chain has the following nucleotide sequence: TTACAGGTTTTAT. Determine the nucleotide sequence on the mRNA, the anticodons of the corresponding tRNAs, and the amino acid sequence of the corresponding fragment of the protein molecule using the genetic code table. 13. Protein consists of 100 amino acids. Determine how many times the molecular weight of the gene region encoding this protein exceeds the molecular weight of the protein, if the average molecular weight of an amino acid is 110, and a nucleotide is 300. Explain your answer. 14. 30 tRNA molecules participated in the translation process. Determine the number of amino acids that make up the synthesized protein, as well as the number of triplets and nucleotides in the gene that encodes this protein. 15. It is known that all types of RNA are synthesized on a DNA matrix. The fragment of the DNA molecule, on which the central loop region of tRNA is synthesized, has the following nucleotide sequence ATAGCTGAACGGACT. Set the nucleotide sequence of the tRNA site that is synthesized on this fragment, and the amino acid that this tRNA will transfer during protein biosynthesis, if the third triplet corresponds to the tRNA anticodon. Explain the answer. To solve the problem, use the table of the genetic code. 16. The section of the DNA molecule has the following composition: - GATGAATAGTGCTTC. List at least 3 consequences that an accidental substitution of the seventh nucleotide from thymine to cytosine (C) can lead to. 17. A fragment of the DNA chain has the nucleotide sequence GTGTATGGAAGT. Determine the nucleotide sequence on the mRNA, the anticodons of the corresponding tRNA, and the amino acid sequence in the protein fragment using the genetic code table. 18. A fragment of the ribosomal gene has the sequence ATTGCCGATTACCAAAGTACCCAAT. What will be the RNA sequence encoded by this region? What class of RNA will it belong to? What will be its function? 19. A fragment of the ribosomal gene has the sequence CCCTATGTATTACGGAAGAGGCATT. What will be the RNA sequence encoded by this region? What class of RNA will it belong to? What will be its function? 20. A section of a DNA molecule has the following composition: GATGAATAGTGCTTC. List at least 3 consequences that an accidental replacement of the seventh nucleotide of thymine with cytosine (C) can lead to. 21. tRNA anticodons are given. Using the table of the genetic code, determine the sequence of amino acids in a fragment of a protein molecule, mRNA codons and triplets in a fragment of a gene encoding this protein. tRNA anticodons: GAA, HCA, AAA, ACC. 22. It is known that all types of RNA are synthesized on a DNA matrix. The DNA chain fragment, on which the tRNA central loop region is synthesized, has the following nucleotide sequence: TCCGCATACGATAGG. Determine the nucleotide sequence of the tRNA region that is synthesized on this fragment and the amino acid that this tRNA will transfer during protein biosynthesis if the third triplet is the tRNA anticodon. Explain the answer. To solve the problem, use the table of the genetic code. 23. IRNA consists of 156 nucleotides. Determine the number of amino acids included in the protein it encodes, the number of tRNA molecules involved in the biosynthesis of this protein, and the number of triplets in the gene encoding the primary structure of the protein. Explain your results.

24. As a result of a mutation in a fragment of a protein molecule, the amino acid threonine (tre) was replaced by glutamine (hln). Determine the amino acid composition of a fragment of a molecule of a normal and mutated protein and a fragment of a mutated mRNA, if the normal mRNA has the sequence: GUCACAGCGAUCA-AU. Explain the answer. To solve the problem, use the table of the genetic code. 25. It is known that all types of RNA are synthesized on a DNA matrix. The fragment of the DNA chain, on which the region of the central loop of tRNA is synthesized, has the following nucleotide sequence: ACGGTAATTHCTATC. Determine the nucleotide sequence of the tRNA region that is synthesized on this fragment and the amino acid that this tRNA will transfer during protein biosynthesis if the third triplet corresponds to the tRNA anticodon. Explain the answer. To solve the problem, use the table of the genetic code. 26. As a result of a mutation in a fragment of a protein molecule, the amino acid phenylalanine (phene) was replaced by lysine (lys). Determine the amino acid composition of a fragment of a molecule of a normal and mutated protein and a fragment of a mutated mRNA, if the normal mRNA has the sequence: CUCGCAACGUUCAAU. Explain the answer. To solve the task, use the table of the genetic code. 27. Polypeptide biosynthesis involves tRNA molecules with anticodons UAC, UUU, GCC, CAA in this sequence. Determine the corresponding nucleotide sequence on mRNA, DNA and amino acid sequence in a protein fragment using the genetic code table. 28. In the biosynthesis of a fragment of a protein molecule, tRNA molecules with anticodons ACC, HUC, UGA, CCA, AAA were involved in succession. Determine the amino acid sequence of the synthesized fragment of the protein molecule and the nucleotide sequence of the region of the double stranded DNA molecule, which encodes information about the primary structure of the protein fragment. Explain the sequence of your actions. To solve the problem, use the table of the genetic code. 29. In the biosynthesis of a fragment of a protein molecule, tRNA molecules with anticodons AAG, AAU, GGA, UAA, CAA sequentially participated. Determine the amino acid sequence of the synthesized fragment of the protein molecule and the nucleotide sequence of the region of the double stranded DNA molecule, which encodes information about the primary structure of the protein fragment. Explain the sequence of your actions. To solve the problem, use the table of the genetic code. 30. In the biosynthesis of a fragment of a protein molecule, tRNA molecules with anticodons AGC, ACC, GUA, CUA, CGA were involved in succession. Determine the amino acid sequence of the synthesized fragment of the protein molecule and the nucleotide sequence of the region of the double stranded DNA molecule, which encodes information about the primary structure of the protein fragment. Explain the sequence of your actions. To solve the problem, use the table of the genetic code. 31. A fragment of a double-stranded DNA molecule is given. Using the table of the genetic code, determine which fragments of protein molecules can be encoded by the DNA encoded by this region. List at least three steps in this process. Prove the answer. DNA AAA - TTT - GGY - CCC 32. It is known that all types of RNA are synthesized on a DNA matrix. The DNA chain fragment on which the tRNA central loop region is synthesized has the following nucleotide sequence: TGCCATTTCGTTACG. Set the nucleotide sequence of the tRNA region that is synthesized on this fragment and the amino acid that this tRNA will transfer in TTT - AAA - CCC - GGG

the process of protein biosynthesis, if the third triplet corresponds to the tRNA anticodon. Explain the answer. To solve the problem, use the table of the genetic code. 33. An mRNA chain fragment has a nucleotide sequence: CGAGUAUGCUGG. Determine the nucleotide sequence on one strand of the DNA molecule, tRNA anticodons, and the amino acid sequence that corresponds to the given gene fragment using the genetic code table. 34. A fragment of a DNA chain has the following nucleotide sequence: TTA GAA TAT CAG GAC Determine the nucleotide sequence on mRNA, the anticodons of the corresponding tRNA and the amino acid sequence in the fragment of the protein molecule encoded by the specified DNA fragment, using the genetic code table 35. The DNA chain fragment has the following nucleotide sequence: TTA GAA TAT CAG GAC Determine the nucleotide sequence on the mRNA, the anticodons of the corresponding tRNA, and the amino acid sequence in the protein fragment encoded by the specified DNA fragment using the genetic code table. 36. It is known that all types of RNA are synthesized on a DNA matrix. The fragment of the DNA molecule, on which the region of the central loop of tRNA is synthesized, has the following nucleotide sequence: CGTGGGGCTAGG CTG. What amino acid will be transferred by tRNA synthesized on this DNA fragment if its third triplet corresponds to an anticodon? Explain the answer. Use the genetic code table to solve. 37. A fragment of the DNA chain has the nucleotide sequence TTTAGCTGTCGGAAG. As a result of the mutation that occurred in the third triplet, the third nucleotide was replaced by nucleotide A. Determine the nucleotide sequence on the mRNA from the original fragment of the DNA chain and the changed one. Explain what will happen to a fragment of a protein molecule and its properties after the resulting DNA mutation. Use the genetic code table to solve. 38. The genetic apparatus of a virus is represented by an RNA molecule, a fragment of which has the following nucleotide sequence: GUGAAAAGAUCAUGCGUGG. Determine the nucleotide sequence of a double-stranded DNA molecule, which is synthesized as a result of reverse transcription on the RNA of the virus. Set the sequence of nucleotides in mRNA and amino acids in the protein fragment of the virus, which is encoded in the found fragment of the DNA molecule. The template for mRNA synthesis, on which viral protein is synthesized, is the second strand of double stranded DNA. To solve the problem, use the table of the genetic code. 39. A fragment of a DNA chain has the nucleotide sequence TTTAGCTGTCGGTAG. As a result of the mutation that occurred in the fifth triplet, the first nucleotide T was replaced by nucleotide A. Determine the nucleotide sequence on the mRNA from the original fragment of the DNA chain and from the changed one. Using the genetic code table, determine the amino acid resulting from the mutation and explain what can happen to the protein molecule and its properties after the resulting DNA mutation. "Cell division" 1. The total mass of all DNA molecules in 46 somatic chromosomes of one somatic human cell is 6x10-9 mg. Determine the mass of all DNA molecules in the spermatozoon and in the somatic cell before and after division. Explain the answer.

2. What division of meiosis is similar to mitosis? Explain how it is expressed and what set of chromosomes in the cell leads to. 3. Explain what are the similarities and differences between mutational and combinative variability. 4. What chromosome set is typical for the cells of the embryo and endosperm of the seed, leaves of a flowering plant. Explain the result in each case. 5. The chromosome set of wheat somatic cells is 28. Determine the chromosome set and the number of DNA molecules in one of the cells of the ovule before the start of meiosis, in the anaphase of meiosis 1 and in the anaphase of meiosis 2. Explain what processes occur during these periods and how they affect the change change in the number of DNA and chromosomes. 6. What chromosome set is typical for the cell nuclei of the epidermis of the leaf and the eight-nuclear germ sac of the ovule of a flowering plant? Explain from what initial cells and as a result of what division these cells are formed. 7. Down's syndrome in humans manifests itself with trisomy of 21 pairs of chromosomes. Explain the reasons for the appearance of such a chromosome set in humans. 8. Indicate the number of chromosomes and the number of DNA molecules in the prophase of the first and second meiotic cell division. What event occurs with chromosomes in the prophase of the first division? 9. The somatic cell of an animal is characterized by a diploid set of chromosomes. Determine the chromosome set (n) and the number of DNA molecules (c) in the cell in meiotic prophase I and meiotic metaphase II. Explain the results in each case. 10. What chromosome set is typical for gametes and spores of the cuckoo flax moss plant? Explain from which cells and as a result of what division they are formed. 11. Drosophila somatic cells contain 8 chromosomes. How will the number of chromosomes and DNA molecules in the nucleus change during gametogenesis before the onset of division and at the end of telophase I of meiosis? Explain the results in each case. 12. A somatic cell of an animal is characterized by a diploid set of chromosomes. Determine the chromosome set (n) and the number of DNA(c) molecules in the cell at the end of meiosis telophase I and meiosis anaphase II. Explain the results in each case. 13 What are the features of meiosis that provide gamete diversity? List at least three features. 14. The somatic cell of an animal is characterized by a diploid set of chromosomes. Determine the chromosome set (n) and the number of DNA molecules (c) in the cell before meiosis I and meiosis prophase II. Explain the results in each case. 15. What chromosome set is typical for gametophyte and sphagnum moss gametes? Explain from what initial cells and as a result of what division these cells are formed? 16. What chromosome set is characteristic for the gametophyte and sphagnum moss gametes? Explain from what initial cells and as a result of what division these cells are formed? 17. Indicate the number of chromosomes and the number of DNA molecules in the prophase of the first and second meiotic cell division. What event occurs with chromosomes in the prophase of the first division?

18. Cattle have 60 chromosomes in their somatic cells. Determine the number of chromosomes and DNA molecules in ovarian cells during oogenesis in interphase before the onset of division and after division of meiosis I. Explain the results obtained at each stage. 19. Drosophila somatic cells contain 8 chromosomes. What number of chromosomes and DNA molecules is contained in the nucleus during gametogenesis before the onset of meiosis I and meiosis II? Explain how such a number of chromosomes and DNA molecules are formed. 20. Consider the human karyotype and answer the questions. 1. What gender is this person? 2. What deviations does the karyotype of this person have? 3. What events can cause such deviations? 21. Consider the human karyotype and answer the questions. 1. What gender is this person? 2. What deviations does the karyotype of this person have? 3. What events can cause such deviations? 22. What chromosome set is typical for vegetative, generative cells and sperm of the pollen grain of a flowering plant? Explain from what initial cells and as a result of what division these cells are formed. 23. Rabbit somatic cells contain 44 chromosomes. How will the number of chromosomes and DNA molecules in the nucleus change during gametogenesis before the onset of division and at the end of telophase I of meiosis? Explain the results in each case. 24. The somatic cells of the Drosophila fly contain 8 chromosomes. Determine the number of chromosomes and DNA molecules in cells during spermatogenesis in the reproduction zone and at the end of the gamete maturation zone. Justify the answer. What processes take place in these zones? 25. What chromosome set is characteristic for the spore, gametophyte and sporophyte of the cuckoo flax moss? From what initial cells and as a result of what division are these stages of moss development formed? 26. What chromosome set is typical for the pulp cells of pine needles and sperm? Explain from what initial cells and as a result of what division these cells are formed.

27. The total mass of all DNA molecules in 46 chromosomes of one human somatic cell is about 6∙10−9 mg. Determine the mass of all DNA molecules in the cell nucleus during spermatogenesis before the start of meiosis and after the end of meiosis. Explain your results. 28. Signs that determine the blood group and Rh factor are not linked. The blood group is controlled by three alleles of one gene – i0, IA, IB. The IA and IB alleles are dominant over the i0 allele. The first group (0) is determined by recessive i0 genes, the second group (A) is determined by the dominant IA allele, the third group (B) is determined by the dominant IB allele, and the fourth (AB) by two dominant alleles IAIB. A positive Rh factor (R) dominates over a negative Rh factor (r). The father has the second blood type and negative Rh, the mother has the first group and positive Rh (homozygous). Make a scheme for solving the problem. Determine possible genotypes of parents, possible blood types, Rh factor and genotypes of children. Explain your results. What law of heredity will manifest itself in this case? 29. What chromosome set is typical for vegetative, generative cells and sperm of the pollen grain of a flowering plant? Explain from what initial cells and as a result of what division these cells are formed. 30. The total mass of all DNA molecules in 46 chromosomes of one human somatic cell is about 6 ∙ 10−9 mg. Determine the mass of all DNA molecules in the nucleus during spermatogenesis before meiosis, after meiosis I and meiosis II. Explain your results. 31. The karyotype of a dog includes 78 chromosomes. Determine the number of chromosomes and the number of DNA molecules in cells during oogenesis in the reproduction zone and at the end of the gamete maturation zone. What processes take place in these zones? Justify your answer (the answer must contain four criteria). 32. The field mouse has 40 chromosomes. How many chromosomes does a male mouse have in spermatogonia, from which the formation of spermatozoa begins, in mature spermatozoa and in embryonic cells? What division leads to the formation of these cells? What cells do they form from? 33. There are 34 chromosomes in the karyotype of an apple tree. How many chromosomes and DNA will be contained in the egg cell of an apple tree, the endosperm cells of its seed and leaf cells? What cells form these cells? 34. The chromosome set of potato somatic cells is 48. Determine the chromosome set and the number of DNA molecules in cells during meiosis in meiosis prophase I and meiosis metaphase II. Explain all your results. 35. The mass of DNA molecules in somatic cells is 6 * 109. What is the mass of DNA molecules before the start of meiosis and in the anaphase of meiosis 1, explain the answer. 36. There are 42 chromosomes in somatic cells of oats. Determine the chromosome set and the number of DNA molecules before the start of meiosis I and in the metaphase of meiosis II. Explain the answer. 37. In Chlamydomonas, the predominant generation is the gametophyte. Determine the chromosome set of an adult organism and its gametes. Explain from what initial cells adult individuals and their gametes are formed, as a result of which division germ cells are formed. 38. The number of chromosomes in the somatic cell of Drosophila 8. Determine the number of chromosomes and DNA molecules in Drosophila during oogenesis in the anaphase of meiosis 1 and prophase of meiosis 2. Explain the results. "Chargaff's Rule"

1. It is known that all types of RNA are synthesized on a DNA template. The fragment of the DNA molecule on which the tRNA site is synthesized has the following nucleotide sequence ATA-GCT-GAA-CHG-ACT. Set the nucleotide sequence of the tRNA region that is synthesized on this fragment. Which mRNA codon will correspond to the anticodon of this tRNA if it carries the GLU amino acid to the site of protein synthesis. Explain the answer. To solve the task, use the table of the genetic code: 2. A gene contains 1500 nucleotides. One of the chains contains 150 A nucleotides, 200 T nucleotides, 250 G nucleotides, and 150 C nucleotides. How many nucleotides of each type will be in the DNA chain that codes for the protein? How many amino acids will be encoded by this DNA fragment? 3. In one DNA molecule, nucleotides with thymine (T) make up 24% of the total number of nucleotides. Determine the number (in%) of nucleotides with guanine (G), adenine (A), cytosine (C) in the DNA molecule and explain the results. 4. DNA chain is given: CTAATGTAACCA. Determine: A) The primary structure of the encoded protein. B) The percentage of different types of nucleotides in this gene (in two chains). C) The length of this gene. D) the length of the protein. 5. Drosophila somatic cells contain 8 chromosomes. Determine how many chromosomes and DNA molecules are contained in the nuclei during gametogenesis before division in the interphase and at the end of the telophase of meiosis I. Explain how such a number of chromosomes and DNA molecules are formed. 6. On the preparation, tissues with the following structures were found: a) a layer of cells closely adjacent to each other, b) cells are separated by a well-developed intercellular substance, c) cells are strongly elongated, and transverse striation is observed in them. Write to which tissue each of these structures belongs. 7. The mRNA chain fragment has the following nucleotide sequence: CUACAAGGCUAU. Determine the nucleotide sequence on DNA, the anticodons of the corresponding tRNAs, and the amino acid sequence of the corresponding fragment of the protein molecule using the genetic code table. 8. The bracken fern sporophyte has 52 chromosomes. How many chromosomes does it have in sporangium cells, in mature spores and in outgrowth cells? What division leads to the formation of these cells? What cells do they form from? 9. A fragment of the DNA nucleotide chain has the sequence CCATAGC. Determine the nucleotide sequence of the second strand and the total number of hydrogen bonds that form between the two strands of DNA. Explain your results. "Energy exchange" 1. Explain the similarities and differences between the biological oxidation of organic substances in a cell and the process of their combustion in inanimate nature.

2. In the process of glycolysis, 112 molecules of pyruvic acid (PVA) were formed. How many glucose molecules have been cleaved and how many ATP molecules are formed during the complete oxidation of glucose in eukaryotic cells? Explain the answer. 3. During the oxygen stage of catabolism, 972 ATP molecules were formed. Determine how many glucose molecules were cleaved and how many ATP molecules were formed as a result of glycolysis and complete oxidation? Explain the answer. 4. In the process of the oxygen stage of catabolism, 1368 ATP molecules were formed. Determine how many glucose molecules were cleaved and how many ATP molecules were formed as a result of glycolysis and complete oxidation? Explain the answer.

The set of chromosomes contained in the nucleus is called chromosome set . The number of chromosomes in a cell and their shape are constant for each type of living organism.

Number (diploid set) of chromosomes in some plant and animal species

Somatic cells usually diploid (contain a double set of chromosomes - 2n). In these cells, the chromosomes are presented in pairs. The diploid set of chromosomes of cells of a particular type of living organisms, characterized by the number, size and shape of chromosomes, is called karyotype . Chromosomes belonging to the same pair are called homologous. One of them is inherited from the paternal organism, the other - from the maternal. Chromosomes of different pairs are called non-homologous . They differ from each other in size, shape, location of primary and secondary constrictions. Chromosomes that are the same in both sexes are called autosomes. The chromosomes on which the male and female sexes differ from each other are called sex chromosomes, or heterochromosomes . A human cell contains 46 chromosomes or 23 pairs: 22 pairs of autosomes and 1 pair of sex chromosomes. Sex chromosomes are referred to as X- and Y-chromosomes. Women have two X chromosomes, while men have one X and one Y chromosome.
sex cells haploid (contain a single set of chromosomes - n). In these cells, the chromosomes are presented in the singular and do not have a pair in the form of a homologous chromosome.

cell division

Chromosomal set

Chromosomal set - a set of chromosomes contained in the nucleus. Depending on the chromosome set, cells are somatic and sexual.

Somatic and germ cells

cell cycle

cell cycle (cell life cycle) - the existence of a cell from the moment it arises as a result of the division of the mother cell to its own division or death. The duration of the cell cycle depends on the type of cell, its functional state and environmental conditions. The cell cycle includes a mitotic cycle and a dormant period.
AT rest period (G 0) the cell performs its inherent functions and chooses a further fate - it dies or returns to the mitotic cycle. In continuously reproducing cells, the cell cycle coincides with the mitotic cycle, and there is no rest period.
Mitotic cycle consists of four periods: presynthetic (postmitotic) - G 1, synthetic - S, postsynthetic (premitotic) - G 2, mitosis - M. The first three periods are the preparation of the cell for division ( interphase), the fourth period is the division itself (mitosis).

Interphase - preparation of a cell for division - consists of three periods.

Interphase periods

division of eukaryotic cells

The basis of reproduction and individual development of organisms is cell division.
Eukaryotic cells have three ways of dividing:

• amitosis (direct division),
• mitosis (indirect division),
• meiosis (reduction division).

Amitosis- a rare way of cell division, characteristic of aging or tumor cells. During amitosis, the nucleus is divided by constriction and the uniform distribution of hereditary material is not ensured. After amitosis, the cell is not able to enter into mitotic division.

Mitosis

Mitosis- a type of cell division, as a result of which daughter cells receive genetic material identical to that contained in the mother cell. As a result of mitosis, two diploid cells, genetically identical to the parent, are formed from one diploid cell.

Mitosis consists of four phases.

Phases of mitosis

The biological significance of mitosis:

• genetic stability is achieved;
• the number of cells in the body increases;
• body grows;
• phenomena of regeneration and asexual reproduction are possible in some organisms.

Meiosis

Meiosis- a type of cell division, accompanied by a reduction in the number of chromosomes. As a result of meiosis, four haploid cells are formed from one diploid cell, genetically different from the mother. During meiosis, two cell divisions occur (the first and second meiotic divisions), and the doubling of the number of chromosomes occurs only before the first division.

Like mitosis, each of the meiotic divisions consists of four phases.

Phases of meiosis

The biological significance of meiosis:

• the basis of sexual reproduction;
• basis of combinative variability.

division of prokaryotic cells

Prokaryotes do not have mitosis or meiosis. Bacteria reproduce asexually - cell division with the help of constrictions or partitions, less often budding. These processes are preceded by the duplication of the circular DNA molecule.
In addition, bacteria are characterized by a sexual process - conjugation. When conjugated through a special channel formed between two cells, a DNA fragment of one cell is transferred to another cell, that is, the hereditary information contained in the DNA of both cells changes. Since the number of bacteria does not increase, for correctness, the concept of "sexual process" is used, but not "sexual reproduction".

1. In an animal cell, the diploid set of chromosomes is 34. Determine the number of DNA molecules before mitosis, after mitosis, after the first and second divisions of meiosis.

Decision: By condition, 2n=34.

Genetic set:

1. Before mitosis, 2n4c, so this cell contains 68 DNA molecules;
2. After mitosis, 2n2c, so this cell contains 34 DNA molecules;
3. After the first division of meiosis n2c, so this cell contains 34 DNA molecules;
4. After the second division of meiosis, nc, so this cell contains 17 DNA molecules.