Cytoskeleton

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Cytoskeleton Mitosis
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The Cytoskeleton

• 3 types of fibres
• Microfilaments - thinnest
• Microtubules - thickest
• Intermediate filaments
• All function in maintaining cell shape
• Only found in eukaryotes

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Microtubules

• Hollow rods of protein
• FUNCTIONS
• Flagella and cilia of eukaryotic cells
• Organelle movement in a cell
• Involved in mitosis

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• Flagella motility (e.g. sperm tails)
• Cilia motility, and move fluid past cells (e.g.
  cilia in lungs)

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Structure

• ALL eukaryotic cilia and flagella have the same
  internal structure
• 92 arrangement
• Sheathed in extension of plasma membrane

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What causes the motion?

• Motor molecules allow microtubules to walk past
  one another
• Requires energy
• Dynein kinesin

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Organelle movements

• Microtubules act like highways for movement of
  organelles
• E.g. vesicle transport from ER to Golgi to plasma
  membrane

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Quick camouflage

• Pigment granules move on kinesin motors

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Microtubules are involved in mitosis

• Mitosis division of the chromosomes
• Prophase, metaphase, anaphase, telophase
• Cytokinesis division of the cytoplasm and its
  contents

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Interphase G1, S G2
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Interphase

• 90 of the cycle spent in interphase
• During G1 phase, the cell is growing
• During S phase, the chromosomes are duplicated
• During G2 phase, organelles and centrosomes
  reproduce in preparation for division
• By the end of G2, cell is about twice the size
  compared to beginning of interphase

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Whats a centrosome?

• Contains 2 centrioles
• Centriole microtubule triplets arranged in a
  ring
• Involved in spindle formation but

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Mitosis - The Movie!
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Prophase

• Chromatin condenses into visible chromosomes
• Each chromosome is composed of 2 sister
  chromatids
• double-stranded
• 46 double-stranded chromosomes (96 chromatids)

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Prophase

• Nucleoli and nuclear membrane disappear
• Spindle of microtubules forms from centrosomes
• Causes the centrosomes to move to the poles

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Spindle Apparatus
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Prophase
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Metaphase

• 46 double-stranded chromosomes (92 chromatids)
  line up in centre of cell
• Non-kinetochore microtubules interact with those
  from opposite pole of cell

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Metaphase
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Anaphase

• Non-kinetochore microtubules lengthen
• Kinetochore microtubules shorten
• Sister chromatids separate at the centromere
• 46 chromatids (i.e. single-stranded chromosomes)
  move to one pole, 46 move to the other pole

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Anaphase
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Telophase Cytokinesis

• Essentially the reverse of prophase
• Nuclear membranes and nucleoli re-form,
  chromosomes uncoil into chromatin
• Cytokinesis occurs (division of the cytoplasm and
  its contents)
• One cell divides into two identical progeny cells

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Cell division

• In animal cells, cleavage furrow forms
  (microfilaments tighten like a belt)
• In plant cells, vesicles of cell wall material
  aggregate in centre
• Fuse to form a cell plate

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Cell division
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Summary - animal cells
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Summary - plant cells