Mitosis Chapter 10

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MitosisChapter 10
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Lecture Topics

• Prokaryote Eukaryote
• The cell cycle
• Mitosis
• The regulation of cell division

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Cell Division inProkaryotes and Eukaryotes

• Prokaryotes undergo simple fission to produce
  identical daughter cells asexual reproduction.
• No mitotic spindle (they have no cytoskeleton)
• Single circular DNA molecule separates as the
  cell wall separates the new cells
• Eukaryotes use mitosis to produce identical
  daughter cells by means of asexual reproduction
• Complex process involving two cytoskeletal
  systems
• Linear DNA strands separated by complex motor
  systems
• Prokaryotes do have sex
• Eukaryotes use meiosis to produce a new mix of
  genes by means of sexual reproduction.
• Meiosis similar to mitosis but different in detail

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Eukaryotic Chromosomes

• The genetic material is held on chromosomes.
• During cell division, chromosomes must be
  precisely duplicated.
• Eukaryotes can have one to many chromosomes.
• Usually linear arrangement of nuclear genes
  circular only in mitochondria and chloroplasts
• Nuclear DNA protected by extensive wrapping
• Genes held on the chromosomes like beads on a
  string
• Recent work from the Human Genome Project
  indicates 30,000 genes, fewer than expected

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Eukaryotic Chromosomes

• Stained with Ab against the centromeres (yellow)

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The 23 Chromosomes of Homo sapiens

• Mitotic (doubled) chromosomes taken from a white
  blood cell at metaphase
• 23 chromosome types, 46 total
• Stained with Giemsa stain to reveal differences
  in the DNA/protein associations.
• Banding distinctive to each chromosome
• What was the sex of this individual?

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The Eukaryotic Cell Cycle

• Interphase (blue arrows)
• G1 Gap 1
• Normal housekeeping
• Basic cell functions
• Is usual stopping point
• S Synthesis of DNA
• Centrioles divide too
• G2 Gap 2
• Preparation to divide

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M Phase

• Mitosis (pink arrow)
• Prophase
• Chromosomes condense
• Nuclear membranes degrade
• Metaphase
• Chromosomes line up
• Anaphase
• Chromosomes separate
• Telophase
• Nuclei reform
• Cytokinesis (yellow)
• Daughter cells separate

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Chromosomal Organization Interphase and M phase

• In G1 the chromosomes are singlet because they
  are single DNA / histone complexes
• In S the chromosomes duplicate and become duplex.
• Duplex chromosomes are held together by the
  centromere
• Looks like a button
• In G2 chromosomes continue to be duplex
• In M they condense and individual sister
  chromatids become evident

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Chromosome and MTs

• Microtubules (MTs) bind to the centromere region
  at the kinetochore
• Each sister chromatid has a kinetochore
• Chromatids separate during mitosis
• MTs pull chromosomes apart by applying pressure
  at the kinetochores

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The Mitotic Spindle MTs MT-Associated
Structures

• Poles
• Centrioles
• Pericentriolar material
• Asters
• Astral microtubules
• Spindle
• Pole-to-pole MTs
• Chromosomes
• Kinetochores
• Kinetochore MTs

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Mitosis Early Stages

• Interphase
• Normal functions
• Upon trigger, chromosomes centrioles duplicate
• Prophase
• Early nuclear envelope degrades, chromosomes
  start to condense
• Late chromosomes thicken, spindle forms between
  centrioles
• Metaphase
• Spindle fibers attach to kinetochores
• Chromosomes line up at cell equator

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Mitosis Formation of New Cells

• Anaphase
• Chromatids separate at centromeres
• Chromosomes move to poles
• Telophase
• Nuclear envelope reforms in each of two daughter
  cells
• Cytokinesis separates two new cells
• Interphase
• Daughter cells are genetically identical to each
  other and the parent cell, but smaller

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Chromosome Structure
G1
G2
M Mitosis
G1
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Animal Cell Cytokinesis

• Cytokinesis is the separation of the two daughter
  cells
• Actin and myosin- dependent
• Chromosome separation is MT-dependent
• Actin/myosin fibers pull like purse-string, nip
  cells apart

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Daughter Cell Production in Plants

• The mitotic spindle forms but has no centrioles
  at the poles
• At cell division, vesicles form out of the Golgi
  over the equatorial plate
• They form a large vesicle and the cell is split
  by the production of the new cell wall

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Regulation of cell division

• Intracellular signals tell cell to undergo
  division
• Cyclin-dependent protein kinases (Cdks) become
  active in the presence of the regulatory protein
  cyclin
• Division based on size and activation by growth
  factors specific to each cell type (e.g.
  Epithelial, nerve, etc), which cause production
  of G1 Cdks
• Cyclin combines with mitosis (or maturation)
  promotion factor (MPF) to activate the Cdks.
• G1 Cdks prepare cell for S, then G2.
• Mitotic Cdks cause chromosome condensation,
  nuclear envelope breakdown, and spindle formation
• Anaphase promoting factor (APF) activates the
  proteolytic digestion of MPF and allows sister
  chromatid to separate