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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

Chapter 9Cell Division and Mitosis

http://www.phschool.com/science/biology_place/biocoach/mitosisisg/intro.html

why do cells divide
Why do Cells divide?
  • Growth
  • Reproduction (for single cell organisms)
  • Repair
cycle of life
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
overview of division mechanisms
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)
chromosomes
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
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  • Proteins called histones tightly bind to DNA and cause spooling into a structural unit called nucleosome
mitosis and chromosome number
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)
cell cycle
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
interphase
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
mitosis overview
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
prophase
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
prometaphase
Prometaphase
  • Nuclear envelope fragments
  • Spindle apparatus attach to the centromere
metaphase m ms
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
anaphase
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
telophase
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
cytokinesis
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
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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
mitosis is amazing
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)
binary fission
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
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Continue…
  • 4- Cell elongates
  • 5- Cytoplasm begins to pinch in
  • 6- divides
cell cycle control
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
regulatory proteins
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
growth factor
Growth Factor
  • A protein released by certain cells that stimulates other cells to grow
density dependent inhibition
Density-dependent inhibition
  • Phenomenon in which crowded cells stop growing
loss of cells cycle in cancer cells
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)
two types of tumors
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)
metastasis
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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