Cell division

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Cell division

• How one cell becomes two

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Mitosis Cytokinesis Cell division

• Most cells in all eukaryotic organisms will
  divide many times throughout the life of the
  organism
• Mitosis is the process by which a cell duplicates
  its genetic materials (chromosomes and prepares
  for cell division
• Cytokinesis is the division of the rest of the
  cell into two different daughter cells
• Prokaryotes also divide through binary fission,
  but this is NOT mitosis/cytokinesis
• In animals, cell division occurs during embryonic
  development, growth, and wound healing
• Errors during cell division can cause cell death
  or cancer

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Mitosis reorganizes DNA in the cell

• Prior to mitosis, the cell creates an exact
  duplicate of its DNA material
• During mitosis, the two copies are reorganized,
  repackaged into two sets of chromosomes, and
  divided to opposite ends of the cell
• In most organisms, mitosis is immediately
  followed by cytokinesis (the cell body dividing
  in two)
• The original cell (mother cell) is identical to
  the two resulting cells (daughter cells)

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Mitosis vocabulary

• Nucleus location of DNA inside the cell
• Nuclear envelope the membrane that separates
  the nucleus from the cytoplasm
• DNA an incredibly long molecule that contains
  genetic blue prints for cell behavior
• Chromatin a loosely bundled coil of DNA. Most
  of the time, DNA is organized in this form, a
  loose rope
• Histones proteins which hold a DNA strand
  together in the form of chromatin
• Chromosome a highly organized form of
  chromatin, a tightly wrapped and carefully
  knotted rope
• Each chromosome is composed of two identical
  parts called chromatids
• Chromatids two halves of a chromosome which
  contain the same genetic information
• DNA exists in the form of chromosomes only during
  mitosis
• Each chromosome looks like an X
• Centromere a bundle of proteins which connects
  the two chromatids of a chromosome, the knot at
  the center of the X
• Microtubules part of a cells cytoskeleton.
  These are tubes of protein which use to pull
  chromosomes apart and to opposite ends of a cell
  during mitosis. They are powered by ATP!
• Mitotic spindle How microtubules are organized
  during mitosis. This is a collection of
  microtubule fibers which is formed to coordinate
  the pulling of apart of chromosomes.
• Metaphase plate the line along which
  chromosomes are lined up during mitosis. This
  arrangement is coordinated by the mitotic
  spindle.

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Chromosome Structure
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5 Phases of Mitosis

• Mitosis is composed of five phases
• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase
• During each phase, different proteins in the cell
  perform specific roles to divide the two copies
  of genetic material
• Cytokinesis occurs after mitosis to create two
  cells

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Prophase

• Chromatin is being organized into chromosomes
  inside the nucleus
• Microtubules are organized into mitotic spindles
  in the cytoplasm
• Nuclear envelope is dissolving
• By the end of prophase
• Chromosomes and mitotic spindle are fully
  organized
• Nuclear envelope has disappeared

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Prometaphase

• Chromosomes move towards each other and into the
  center of the cell
• Microtubules move into the nuclear region and
  begin to connect to chromosomes at the centromere
• Microtubules organize into two mitotic spindles,
  one at each end of the cell

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Metaphase

• The mitotic spindle is fully organized, and has
  pulling the chromosomes to the center of the cell
• The spindle aligns chromosomes so that each
  centromere is lined up along the metaphase plate
  (the center of the cell)

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Anaphase

• Each chromosome is pulled apart into two
  chromatids (halves) at the centromere
• Microtubule fibers contract (using ATP!), pulling
  chromatids to opposite ends of the cell towards
  the two spindles

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Telophase

• Chromatids arrive at opposite ends of the cell
  and begin to unfold into loose coils of
  chromatin
• New nuclear envelopes begin to form around the
  chromatin to create two nuclei
• Spindle fibers disperse into the cytoplasm
• The cell membrane begins to cleave in preparation
  for cytokinesis

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Cytokinesis

• The cell membrane is being pinched off to form
  two separate compartments
• Cytoplasm and organelles are being divided
  between the two forming cells
• At the end of cytokinesis, the membrane fuses to
  create two daughter cells which contain identical
  copies of DNA, and equal amounts of cytoplasm and
  organelles
• Cell division is complete!

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Cell division movies

• http//www.youtube.com/watch?vVlN7K1-9QB0
• http//www.youtube.com/watch?vCzPGhYiGyZ8feature
  related
• Embryonic division in the worm c.elegans
  http//www.youtube.com/watch?vzsgOl04PESINR1
• http//www.cellsalive.com/mitosis.htm