CHAPTER 12 THE REPRODUCTION OF CELLS

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CHAPTER 12THE REPRODUCTION OF CELLS
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I. Reproduction, Growth, and Repair

• Perpetuation of life based on cell division
• Unicellular organisms reproduce entire organisms
  by cell division
• Cell division allows growth and development of
  fertilized egg and replacement of damaged or dead
  cells in multicellular organisms
• Cell division is a complex process that passes on
  genome from one generation of cells to next

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II. Binary Fission

• Prokaryotes reproduce by binary fission
• Chromosome is replicated, each copy remains
  attached to plasma membrane at adjacent sites
• Membrane grows and separates chromosomes copies
• Bacterium grows, plasma membrane pinches inward
• Cell wall forms between two chromosomes

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III. Eukaryotic Genome

• Chromosomes Threadlike structures composed of
  DNA and protein
• Each species has characteristic number (humans
  46)
• Gametes (egg/sperm) contain half the somatic cell
  number

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• Chromatin A DNA-protein complex organized into
  a long, thin fiber that is folded and coiled to
  form the chromosome

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• Mitosis Nuclear division during which
  duplicated chromosomes are evenly distributed
  into 2 daughter nuclei
• Cytokinesis Cytoplasmic division

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IV. Cell Cycle

• Definition Well-ordered sequence of events
  between the time a cell divides and the time its
  daughter cells divide

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Cell cycle alternates between phases (Fig 11.5)
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• M phases Phase during which cell divides
  (shortest phase) and includes
• Mitosis
• Cytokinesis

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• Interphase nondividing phase, includes most of
  cells growth and metabolic activities
• 90 of cell cycle
• Cell grows and copies its chromosomes
• Consists of 3 periods

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• G1 Phase First growth phase (proteins are made)
• S Phase Synthesis phases when DNA is
  synthesized as chromosomes are duplicated
• G2 Phase Second growth phase (proteins and
  organelles are made)

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C. Stages of mitotic cell division

• G2 phase of Interphase
• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase and Cytokinesis

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V. Mitotic Spindle Distributes Chromosomes

• During prophase, the mitotic spindle forms in the
  cytoplasm from microtubules (alpha/beta tubulin)
  and other proteins
• Spindle microtubules radiate from centrosomes
• Some spindle microtubules attach to kinetochores
  (protein structure on centromere)

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• Kinetochore microtubules arrange and align
  chromosomes on metaphase plate
• Kinetochore microtubules shorten and pull
  chromatids to opposite poles
• Nonkinetochore microtubules elongate the whole
  cell along the polar axis during anaphase

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VI. Cell Division Cues

• Normal growth, development and maintenance depend
  on rate of mitosis
• Human skin cells divide frequently
• Liver cells only divide in appropriate situations
• Nerve, muscle and other specialized cells do not
  divide in mature humans

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B. Factors that influence cell division

• Growth factors regulatory substances

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• Density-dependent inhibition crowding inhibits
  cell division

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3. G1 Phase Restriction point determines
whether a cell is destined to divide

• If destined to divide, it progresses beyond the
  restriction point into the S phase when DNA
  synthesis begins
• If not destined to divide, it may exit from cell
  cycle and switch to nondividing state G0 phase
• Cell Size Ration of cytoplasmic volume to
  genome size

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VII. Cyclical Changes in Regulatory Changes

• The ordered sequence of cell cycle events is
  synchronizes by rhythmic changes in regulatory
  proteins protein kinases
• Catalyze phosphorylation of target proteins
• Phosphorylation induces a conformational change
  in target protein ? activation of inactivation

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• Cyclical changes in kinase activity are
  controlled by cyclins
• Protein kinases that regulate cell cycles are
  cyclin-dependent kinases (Cdks) only active
  when attached to cyclin
• Cdk activity changes in response to cyclin
  concentration

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VIII. Cancer Cells

• Cancer cells do not respond normally to controls
  on cell division divide excessively

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B. Tumor unregulated mass of cells w/normal
tissue

• Benign cells remain a original site may be
  completely removed
• Malignant cells have the ability to spread to
  other parts of the body (cancer). They may have
• Unusual chromosome number
• Aberrant metabolism
• Lost attachment to neighboring cells
• Metastasis spread of cancer cells beyond their
  original sites

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Normal Tissue Cancerous Tissue