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Cell Division

Cell Division. Mitosis and Meiosis. Chromosomes Chromatin – long strands of DNA wrapped around proteins Chromosome – a rod-shaped structure that forms when a single DNA molecule coils tightly before cell division. Single Chromosome. Duplicated Chromosome.

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Cell Division

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  1. Cell Division Mitosis and Meiosis

  2. Chromosomes • Chromatin – long strands of DNA wrapped around proteins • Chromosome – a rod-shaped structure that forms when a single DNA molecule coils tightly before cell division

  3. Single Chromosome Duplicated Chromosome

  4. Chromatid– one of two copies of each chromosome • Sister Chromatid – two identical copies of the chromosome • Centromere – a protein disk that attaches the two chromatids

  5. Single Chromosome Duplicated Chromosome Centromere Chromatid Chromatid Chromatid Sister Chromatids

  6. Human cells have 23 different chromosomes • Contain 2 copies of each chromsome for a total of 46 • Homologous chromosomes – two copies of each chromsome that are similar in shape, size and have similar genetic information

  7. Cell Division • Cell division – process by which new cells are made from an existing cell • Two types of cell division • Mitosis – makes somatic cells (body cells) • Meiosis – makes gametes (sperm and egg)

  8. The Cell Cycle • Cell Cycle – sequence of growth and division of a cell • 5 Phase of the Cell Cycle • G1 • Growth of cell • Makes new proteins and organelles

  9. 2. S • DNA replicates • 3. G2 • Produces proteins needed for mitosis or meiosis • 4. M • Mitosis or Meiosis • Cytokinesis – cytoplasm divides separating into 2 daughter cells • G1, S, and G2 combined are called Interphase • Where the cell spends most of its life

  10. Video

  11. Mitosis • Mitosis – process by which the nucleus of a cell is divided into 2 identical nuclei with the same number of chromosomes • Mitosis is divided into 4 stages

  12. 1. Prophase • Chromatin coils into chromosomes • Nuclear envelope breaks down • Centrioles form and move to opposite poles • As centrioles separate, spindle fibers form which are microtubules (protein cables) • Longest phase of mitosis

  13. 2. Metaphase • Spindle fibers attach to the chromosomes at the centromere • Chromosomes line up in the middle

  14. 3. Anaphase • Centromeres split and sister chromatidsare pulled apart toward opposite poles • Each chromatid may now be called a chromosome

  15. 4. Telophase • Chromosomes reach opposite poles • Spindle fibers break • Chromsomes uncoil • Nuclear envelope forms

  16. Cytokinesis • Two daughter cells are formed

  17. Cytokinesis differs between plants and animals • Animals – the cell membrane pinches in along the center of the cell

  18. Plants – have a cell wall so cell membrane can’t pinch in • Instead a cell plate is laid down across the center

  19. The Cell Cycle

  20. Regulating the Cell Cycle • Normal Cell Growth • Scientists have worked long and hard to discover the factors that initiate and control cell division. • A clear understanding of these control factors can benefit medical research. • Scientists have found that a specific protein called cyclin regulates the cell cycle.

  21. Uncontrolled Cell Growth • Occasionally cells lose control of the cell cycle • This loss of control may be caused by… • Environmental factors • Changes in enzyme production • Cancer is a result of uncontrolled cell division • Cancer cells divide uncontrollably and form masses of cells called tumors. • Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.

  22. Cancer

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