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Chapter 9 Cell Division and Mitosis

Chapter 9 Cell Division and Mitosis. http://www.phschool.com/science/biology_place/biocoach/mitosisisg/intro.html. Why do Cells divide?. Growth Reproduction (for single cell organisms) Repair. Cycle of Life.

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Chapter 9 Cell Division and Mitosis

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  1. Chapter 9Cell Division and Mitosis http://www.phschool.com/science/biology_place/biocoach/mitosisisg/intro.html

  2. Why do Cells divide? • Growth • Reproduction (for single cell organisms) • Repair

  3. Cycle of Life • The cycle of life includes fertilization of gametes, cell division, and growth, production of gametes, and death. • All of life depends of life

  4. Overview of Division mechanisms • Before a cells are able to reproduce, there must be a division of nucleus and its DNA • Mitosis: used by multicellular organisms for growth by repeated division of somatic (body cells) • This division helps cells grow, replace dead, or worn-out cells and repair tissues • Meiosis: only occurs in germ cells that divide to form gametes (sex cells)

  5. Chromosomes • Each chromosomes is a molecule of DNA complexed with proteins • Human DNA is 2 meters long • Prior to cell division, each threadlike chromosomes is duplicated to form two sister chromatids held together by a centromere • The centromere is also the region where the duplicated chromosome will attach to the microtubules of the spindle during nuclear division

  6. Continue • Proteins called histones tightly bind to DNA and cause spooling into a structural unit called nucleosome

  7. Mitosis and Chromosome Number • Each organisms has a definite chromosome number • Example: Humans have 46 chromosomes • Chromosomes exists in pairs (one from each parent) • Humans have 23 pairs of chromosomes • Somatic Cells are diploid (pairs) • Germ cells (sperm and egg cells) are haploid (half the number of total chromosomes)

  8. Cell Cycle • A recurring sequence of events that extends from the time of a cell’s formation until each division is complete • Three phases of cell cycle: Interphase, Mitosis , and Cytokinesis

  9. Interphase • Is the portion of the cell cycle is which the cell prepares for cell division (nuclear and cytoplasmic) • Three phases of Interphase • G1 phase: Carbohydrates, lipids, and proteins for cell’s own use and for export assembled • S phase: DNA is copied and proteins are synthesized used in organizing the condensed chromosomes • G2 phase: the proteins that will drive mitosis to completion are produced

  10. Mitosis Overview • Nuclear Division that occurs in four phases: Prophase, Metaphase, Anaphase, and Telophase (PMAT) • Spindle apparatus (fibers) moves toward chromosomes • Composed of two sets of microtubules • Extend from two poles of cell and overlap at the cell’s equator

  11. Prophase • Chromosomes become visible as rodlike units, each consisting of two sister chromatids • Nuclear envelope begins to break down • Spindle apparatus move toward the poles

  12. Prometaphase • Nuclear envelope fragments • Spindle apparatus attach to the centromere

  13. Metaphase (M&Ms) • Longest Stage of Mitosis • Nuclear membrane breaks up completely in the transition between pro- and metaphase • Chromosome aligns at the cell’s equator, halfway between the poles—also known as the metaphase plate

  14. Anaphase • Sister chromatids separate and move toward opposite poles • Spindle apparatus shorten and pull the chromosomes toward the poles • Once separated each chromatid is now an independent chromosomes

  15. Telophase • Two daughter chromosomes of each original chromatid pair at opposite pair • Chromosome return to the threadlike form typical of chromosome • Each daughter cell has the same number of chromosomes as the parent cell

  16. Cytokinesis • Division of cytoplasm • Plants • Because of rigid cell wall, the cytoplasm of plant cells can not simply pinch off, the plant cell forms a cell plant to separate the two nucleus • Made from vesicles derived from the Golgi apparatus

  17. Continue… • The flexible plasma membrane of animal cells can be squeezed in the middle to separate the two daughter cells • First sign of cleavage is the appearance of a cleavage furrow, a shallow groove in the cell surface near the old metaphase plate

  18. Mitosis is amazing!!! • Mitosis is accomplished with astonishing accuracy • There are times when mistakes happen (too many chromosomes or chromosomes deleted). • This is known as a mutation (genetic mistakes)

  19. Binary Fission • Prokaryotes cell division • 1- Bacterium have circular chromosomes replicate and move apart • 2- the point chromosome replication is known as origin of replication • 3- Each origin of replication will move opposite end of the cell

  20. Continue… • 4- Cell elongates • 5- Cytoplasm begins to pinch in • 6- divides

  21. Cell Cycle Control • Cell cycle control system: a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle • Checkpoint: in the cell cycle is a critical control point where stop and go-ahead signals can regulate the cycle • Animal cells generally have built in stop signals to halt the cell cycle • 3 major checkpoints: G1, G2, M phases

  22. Regulatory Proteins • 1- Kinases: drives the cell cycle • Present at constant concentration throughout the entire cell cycle throughout the entire cell cycle • 2- Cyclin: attaches to kinases • Cyclically fluctuating in the cell cycle • At checkpoint times is when you see the fluctuating • This helps the cell have the correct number of chromosomes

  23. Growth Factor • A protein released by certain cells that stimulates other cells to grow

  24. Density-dependent inhibition • Phenomenon in which crowded cells stop growing

  25. Loss of cells cycle in cancer cells • Cancer cells do not respond to the body’s control mechanisms • Transformation the process that converts a normal cell to a cancer cell • Immune system recognize a transformed cells and destroys it • However, if the cell evades destruction it may proliferate and form a tumor (a mass of abnormal cells within otherwise normal tissue)

  26. Two types of tumors • 1- Benign Tumor: abnormal cells remain at the original site • 2- Malignant tumor: becomes invasive enough to impair the functions of one or more functions (this is when a person have cancer)

  27. Metastasis • Spread of cancer cells to locations distant from their original site • This is usually done through the blood vessels and lymph vessels

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