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Cell Division

Cell Division. Ajith Sominanda Department of Anatomy Faculty of Medicine University of Peradeniya. Need of the cell division. For growth and development of the organism To replace worn out cells & tissues To make offspring. For growth and development of the organism.

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Cell Division

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  1. Cell Division Ajith Sominanda Department of Anatomy Faculty of Medicine University of Peradeniya

  2. Need of the cell division • For growth and development of the organism • To replace worn out cells & tissues • To make offspring

  3. For growth and development of the organism

  4. To replace worn out cells & tissues Copy right : M. M. GODLEWSKI1, M. SLUPECKA1,2, J. WOLINSKI2, T. SKRZYPEK3, H. SKRZYPEK4, T. MOTYL1, R. ZABIELSKI1,2

  5. To replace worn out cells & tissues

  6. To make offspring

  7. Somatic cell division versus gametogenesis Genetic materials do not reduce 2n  2n Genetic materials reduce 2n  n

  8. Cell division includes nuclear and cytoplamic division • Nuclear division Karyokinesis • Cytoplasmic division Cytokinesis

  9. Life cycle of the dividing cell: Cell cycle • Eukaryotic cells passes a sequence of events from a new cell until it reproduce daughter cells; the cell cycle. • How often a cell divides depends on the type of cell • Cells in root of hair, Gut cells, bone marrow cells divide rapidly • Mature muscle cells or neurons do not divide

  10. Cell cycle

  11. Components of the cell cycle s Resting cell G-0 Signal G-1 Initiation of cell division / First Gap S DNA replication G2 Preparation for mitosis / Rechecking M Mitosis / movement of replicated DNA

  12. Components of cell cycle cont.. Interval between two mitoses is called interphase G1 & G2 are Gaps

  13. Interphase • The cell may spend as much as 90 percent of the cell cycle in interphase • The ell perform its normal cellular functions during this phase • Between Gaps (G1 & G2) DNA replicates

  14. Timing • Typical cell cycle usually lasts for 10 to 20 hours. • The S phase takes about 3 to 6 hours • G2 phase is shorter than S phase.

  15. Mitotic phase Replicated DNA (chromosomes) are separated during mitosis and distributed into daughter cells that form through cytokinesis.

  16. Mitosis The event in the cell cycle that separates replicated chromosomes (sister chromatids) into two new cells (daughter cells) Chromosomes Chromatids / Sister chromatids

  17. Chromosome & duplicated chromosome

  18. Mitosis has 4 stages in which nuclear events are visible light microscopically • Prophase • Metaphase • Anaphase • Telophase

  19. Prophase • Characterized by formation of Spindle • Mitotic spindle: Composed of microtubules Formed by centrioles • Chromosomes become visible and later chromatids appears and held together by centromeres • Nuclear membrane disintegrates

  20. Metaphase • Chromosomes moves to the equator of the cell and form Metaphase plate

  21. Anaphase • Sister chromatids moves towards the opposite poles of the spindle

  22. Telophase • Chromatids becomes chromosomes and then chromatin • Nuclear envelop re-forms • Cytokinesis occur

  23. Summary A B Prophase ? Metaphase ? Anaphase ? Telophase ? C D

  24. Gametogenesis

  25. Cell cycle of the germ cells Genetic materials do not reduce 2n  2n Genetic materials reduce 2n  n

  26. Cell cycle of the germ cells

  27. Reduction of genetic materials and formation of gametes; a whole mark in sexual reproduction

  28. Meiosis • Type of cell division in Eukaryotes that makes gametes • Similar to mitosis but diploid cells become haploid (sperm (n), Ovum (n)) • Has two divisions: • Meiosis I • Interphase (DNA replicates) • Prophase I • Metaphase I • Anaphase I • Telophase I • Meiosis II • Interphase (No DNA replication) • Prophase II • Metaphase II • Anaphase II • Telophase II

  29. Meiotic division 1 • During interphase DNA replicates (4n) • Homologous chromosomes stay together in prophase I (cross over / recombination occurs) • Homologous chromosome pairs align in equatorial plane during metaphase I • Each homologous chromosome moves to opposite pole randomly during anaphase • Cytokinesis completes giving rise to haploid cells

  30. Meiotic division 1

  31. Meiotic division 2

  32. Comparison of mitosis and meiosis

  33. Cross over/ Recombination of parts of chromosomes in prophase I Chiasma synaptonemal complex

  34. Prophase has sub divisions

  35. Assortments of Chromosomes in metaphase I • Independent assortment of chromosomes during Metaphase I leads to mixing of genetic materials (genetic diversity) inherited from two parents

  36. Uncontrolled cell division:Tumors • Cells in a cancerous tumor reproduce at an abnormally fast rate and become irregular in appearance. • When individual cells metastasize (travel from the original tumor), the cancer can spread.

  37. Thank you

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