G2 checkpoint

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Cell-Cycle Checkpoints
G2 checkpoint
Pass this checkpoint if cell size is
adequate chromosome replication is
successfully completed
M
Mitosis
G2
Second gap
Metaphase checkpoint
Pass this checkpoint if all chromosomes are
attached to mitotic spindle
G1
First gap
G1 checkpoint
DNA synthesis
Pass this checkpoint if cell size is
adequate nutrient availability is sufficient
growth factors (signals from other cells) are
present
S
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Unreplicated chromosomes
Chromosome
Number of chromosomes 4
3
Replicated chromosomes
Chromosome
Sisterchromatids
Centromere
Number of chromosomes 4
4
Parent cell
Replicated chromosomescondense at the start of
mitosis
Mitosis
During mitosis, sister chromatids separate
andtwo daughter cells are formed.
Parent cell and daughter cell contain thesame
complement of chromosomes.
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PRIOR TO MITOSIS
MITOSIS
Chromosomes replicate,forming sister chromatids
Sister chromatids separate
Early mitotic spindle
Centrosomes
Kinetochore
Centrioles
2. Prophase Chromosomescondense and mitotic
spindle begins to form. Nuclear envelope breaks
down.
3. MetaphaseChromosomes migrate to middle of
cell
1. Chromosomesreplicate in parent cell (S
portion of interphase).
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4. Anaphase Sister chromatidsseparate.
Chromosomes are pulled to opposite poles of the
cell.
5. Telophase The nuclear envelope reforms.
Cytokinesis The cell divides.
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Unregulated cell division can lead to cancer

• Mutations in genes that encode cell cycle
  proteins can lead to unregulated growth,
  resulting in tumor formation and ultimately
  invasion of cancerous cells to other organs.

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Cancerous cells may arise from mistakes in
mitosis.
Sister chomatids separate
Sister chomatids dont separate
Cell becomescancerous
Cell functions normally
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Definitions

• Centrosome cellular organelle
• "microtubule organizing center"
• an area in the cell where microtubules are
  produced.
• Centrioles pair of small organelles within the
  centrosome
• made up of a ring of nine groups of microtubules
• Mitotic Spindle - network of microtubules formed
  during prophase.
• Some microtubules attach to the kinetochores and
  help draw the chromosomes apart during anaphase

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• During animal cell division, the centrosome
  divides and the centrioles replicate (make new
  copies).
• The result is two centrosomes, each with its own
  pair of centrioles.
• The two centrosomes move to opposite ends of the
  nucleus.
• From each centrosome, microtubules grow into a
  "spindle" which is responsible for separating
  replicated chromosomes into the two daughter
  cells.

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Definitions (cont.)

• Centromere region where daughter chromatids are
  held together
• Kinetochore region adjacent to the centromere
  where the spindle fibers attach
• Metaphase Plate - the plane of the equator of the
  spindle into which chromosomes are positioned
  during metaphase