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  1. 1. The Cell Cycle and How Cells Divide E-CLIP EIS Teaching Learning Strategies / Procedures Biology Secondary 6, duration 60 min. Teacher: Mr.Wichai Likitponrak
  2. 2. 2 Look at this Picture! What is this?
  3. 3. 3 Introduction by this VDO!!! https://www.youtube.com/watch?v=vA8aMpHwYh0
  4. 4. 4 Phases of the Cell Cycle The cell cycle consists of Interphase normal cell activity The mitotic phase cell divsion INTERPHASE Growth G 1 (DNA synthesis) Growth G2
  5. 5. 5 Cell Division An integral part of the cell cycle Results in genetically identical daughter cells Cells duplicate their genetic material Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA 20 m100 m 200 m (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).
  6. 6. 6 Structure of Chromosomes
  7. 7. 7 Chromosome Duplication 0.5 m Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centrometers Sister chromatids A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.
  8. 8. 8 Structure of Chromosomes The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores. Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division: Metaphase chromosome Kinetochore Kinetochore microtubules Centromere region of chromosome Sister Chromatids
  9. 9. 9 Phases of the Cell Cycle Interphase G1 - primary growth S - genome replicated G2 - secondary growth M - mitosis C - cytokinesis
  10. 10. 10 Mitosis Some haploid & diploid cells divide by mitosis. Each new cell receives one copy of every chromosome that was present in the original cell. Produces 2 new cells that are both genetically identical to the original cell. DNA duplication during interphase Mitosis Diploid Cell
  11. 11. 11 Mitotic Division of an Animal Cell G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Nonkinetochore microtubules
  12. 12. 12 METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope formingCentrosome at one spindle pole Daughter chromosomes Mitotic Division of an Animal Cell
  13. 13. 13 Mitosis in a plant cell 1 Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from. Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell. 2 3 4 5 Nucleus Nucleolus ChromosomeChromatine condensing
  14. 14. 14
  15. 15. 15 Meiosis Reduces the chromosome number such that each daughter Cell has a haploid set of chromosomes Ensures that the next generation will have: Diploid number of chromosome Exchange of genetic information (combination of traits that differs from that of either parent) Only diploid cells can divide by meiosis. Prior to meiosis I, DNA replication occurs. During meiosis, there will be two nuclear divisions, and the result will be four haploid nuclei. No replication of DNA occurs between meiosis I and meiosis II. Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes 1 2 Homologous chromosomes separate Haploid cells with replicated chromosomes Sister chromatids separate Haploid cells with unreplicated chromosomes Meiosis I Meiosis II
  16. 16. 16 Meiosis Phases Meiosis involves the same four phases seen in mitosis prophase metaphase anaphase telophase They are repeated during both meiosis I and meiosis II. The period of time between meiosis I and meiosis II is called interkinesis. No replication of DNA occurs during interkinesis because the DNA is already duplicated. Prophase I of meiosis Tetrad Nonsister chromatids Chiasma, site of crossing over
  17. 17. 17 Sister chromatids Chiasmata Spindle Centromere (with kinetochore) Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Microtubule attached to kinetochore Tetrad PROPHASE I METAPHASE I ANAPHASE I Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example Pairs of homologous chromosomes split up Tetrads line up Meiosis I is very important to variation (crossing over)
  18. 18. 18 Meiosis II is very similar to mitosis Cleavage furrow PROPHASE II METAPHASE II ANAPHASE II TELOPHASE I AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS Sister chromatids separate Haploid daughter cells forming
  19. 19. 19 A Comparison of Mitosis and Meiosis Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis
  20. 20. 20 MITOSIS MEIOSIS Prophase Duplicated chromosome (two sister chromatids) Chromosome replication Chromosome replication Parent cell (before chromosome replication) Chiasma (site of crossing over) MEIOSIS I Prophase I Tetrad formed by synapsis of homologous chromosomes Metaphase Chromosomes positioned at the metaphase plate Tetrads positioned at the metaphase plate Metaphase I Anaphase I Telophase I Haploid n = 3 MEIOSIS II Daughter cells of meiosis I Homologues separate during anaphase I; sister chromatids remain together Daughter cells of meiosis II n n n n Sister chromatids separate during anaphase II Anaphase Telophase Sister chromatids separate during anaphase 2n 2n Daughter cells of mitosis 2n = 6 A Comparison Of Mitosis And Meiosis
  21. 21. 21 Assignment: Worksheet Pages 7-9 1.1, 1.2 and 1.3 Sent me back in this class !!!