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Chapter 10

Chapter 10. cell cycle and cell division. CELL CYCLE. Sequence of events by which a cell duplicates its genome, synthesises the Other constituents of the cell and eventually divides into two daughter cells. Cell division. DNA replication. Cell growth. Phases of cell cycle.

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Chapter 10

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  1. Chapter 10 cell cycle and cell division

  2. CELL CYCLE Sequence of events by which a cell duplicates its genome, synthesises the Other constituents of the cell and eventually divides into two daughter cells. Cell division DNA replication Cell growth

  3. Phases of cell cycle Eukaryotic- once in 24 hours Cell division- only 1 hour In yeast- once in 90 minutes

  4. m- phase Karyokinesis- nuclear division Cytokinesis- cytoplasm division

  5. G1 PHASE (gap phase) S PHASE (Synthesis phase) G2 PHASE (Gap 2 phase) Interphase (resting phase) Cell growth and DNA replication

  6. G1 Phase Cell is metabolically active and continuously grows but does not replicate its DNA

  7. S- Phase The amount of DNA per cell doubles No Increase in chromosome number

  8. G2- Phase Proteins are synthesised in preparation for mitosis while cell growth continues

  9. G stage (Quiscent stage) 0 Some cells do not divide further, exit G1 phase and enter an inactive stage

  10. M Phase equational division The chromosome number remain same after division Prophase Metaphase Anaphase Telophase

  11. Prophase Initiation of condensation of chromosomal material- two chromatids attached together at the centromere Centrioles begin to move to poles Do not show golgi complex, endoplasmic reticulum, nucleolus and nuclear envolope

  12. Metaphase Complete disintegration of nuclear envolope Condensation of chromatids completed Chromosome is made up of two sister chromatids Small disc shaped kinetochores appearoncentromeres Spindle fibers get attached to kinetochores Chromosomes are arranged at the equator

  13. Anaphase Centromeres split and chromatids separate Chromatids move to opposite poles

  14. Telophase • Chromosomes cluster at opposite poles • And their identity is lost as discrete elements • Nuclear envolope assembeles around the chromosome clusters • Nucleolus, golgi complex and ER reform

  15. Cytokinesis Cell itself is divided into two daughter cells -cytokenisis Karyokenesis- division of nucleus In animals furrow in the plasma membrane deepens and two cells formed In plant cells cell plate forms and grows outward

  16. Significance of mitosis Results in the production of diploid daughter cells with identical genetic complement The growth of multicellualr organisms is due to mitosis Ensures nucleo-cytoplasmic ratio Helps in cell repair continuous Growth in plants is due to mitosis in meristems

  17. Meiosis Specialised cell division -reduces the chromosome number by half Consists of Meiosis I and Meiosis II Identical sister chromatids produced at the S phase Involves pairing of Homologous chromosomes and recombination between them Produces 4 haploid gametes

  18. Meiotic events MEIOSIS I MEIOSIS II PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II

  19. Leptotene Zygotene Pachytene Diplotene Diakinesis MEIOSIS I PROPHASE I Longest phase

  20. MEIOSIS I PROPHASE I Leptotene Chrosomes become gradually visible Chrosomes become compact

  21. MEIOSIS I PROPHASE I zygotene Synapsis forms- pairing of chromosomes sart- Become homologous chromosomes Synaptonemal complex forms- forms tetrad- called bivalents

  22. MEIOSIS I PROPHASE I Pachytene Bivalent chromosomes become clear tetrads Recombination nodules appear Crossing over takes place between homologous chromosomes Enzyme recombinase involoves 2

  23. MEIOSIS I PROPHASE I Diplotene Dissolution of synaptonemal complex Homologous chromosomes tend to separate Bivalents become X – shaped structures-chiasmata

  24. MEIOSIS I PROPHASE I Diakinesis Terminilisation of chiasmata Chromosomes are fully condensed Nucleolus disappears and nuclear envolope breaks down

  25. MEIOSIS I Metaphase I Bivalent chromosomes align on equatorial plate Spindle fibers attach from opposite poles

  26. MEIOSIS I Anaphase I Homologous chromosomes separate Sister chromatids remain Associated at centromeres

  27. MEIOSIS I Telophase I Nucleolus and nucleus reppear Cytokinesis follows- diad of cells Reduction division ……Inter kinesis follows

  28. MEIOSIS II PROPHASE II Resembles normal mitosis Nuclear membrane disappears Chromosomes again become compact

  29. MEIOSIS II METAPHASE II Chromsomes align at equator Spindle fibres attach

  30. MEIOSIS II ANAPHASE II Splitting of centromere of each chromosome Chromosomes of sister chromatids move to opposite poles

  31. MEIOSIS II TELOPHASE II Two groups of chromsomes enclosed in nuclear envolope Cytokineis follows- tetrad of cells forms Four haploid cells formed

  32. Significance of meiosis Conservation of specific chromosome number Increases genetic variability Variations are important for evolution

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