THE CELL CYCLE

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THE CELL CYCLE
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Questions We Have

• Why do cells divide?
• How do cells divide?
• What controls cell division?
• Whats binary fission anyhow?
• What happens when things go wrong?

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Lets Review The Cell Theory?

• All living things are made up of cells and the
  products formed by cells.
• Cells are the units of structure and function.
• In 1855, Rudolf Vichow adds the idea that all
  cells come from preexisting ones (No more
  spontaneous generation).

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So, why do cells divide?

• Growth adding more cells
• Renewal replace old, worn out cells
• Repair fixing things that are broken
• Reproduction creating sperm and egg

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A few terms we need to know

• Genome A cells endowment of DNA. All of its
  genes
• Chromosomes Discrete molecules of DNA and any
  associated proteins called histones.
• Somatic Cells Body cells containing pairs of
  chromosomes (diploid, 2n number 46 in humans).
• Gametes Reproductive cells sperm egg
  containing ½ the chromosome number (haploid, n
  23)
• Sister chromatids Duplicate chromosomes held
  together by a centromere which contains a
  kinetochore for spindle fiber attachment.

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Chromatin Packing
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Terms continued

• Mitosis The division of the nucleus in
  eukaryotic cells.
• Cytokinesis The division of the cytoplasm
  creating two daughter cells.
• Binary fission Prokaryotic cell division

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Binary FissionWhat Bacteria Do
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The Mitotic Cycle in Eukaryotic Cells
Can you pick out the stages of plant cell mitosis?
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The Mitotic Cell CycleThings we didnt tell you
about Freshman year
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Regulation of the Cell Cycle

• The frequency of cell division varies with the
  kind of cell.
• Regulation occurs at the molecular level.
• Regulation by both external and internal controls
  occurs at checkpoints.
• Cell division stops at checkpoints until
  overridden by go-ahead signals.
• G1 checkpoint called restriction point in
  mammalian cells.

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Cell Cycle Check Points
G0
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Cyclins Cyclin-dependent Kinases

• Kinases that drive the cycle are present in
  constant concentration in growing cells.
• Binding cyclins activates kinases.
• Cdks Cyclin dependent kinases
• Cyclin levels rise and fall (they cycle)
• MPF Maturation-promoting factor is a complex of
  cyclins and kinases that promotes passage from G2
  into mitosis.

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External Signals

• Chemical and physical factors.
• Growth factors like PDGF (platelet-derived growth
  factor.
• Density-dependent inhibition.
• Anchorage dependence.

Internal Signals

• Cell surface to volume ratio
• Cell age
• Chromosome number and position

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Cancer

• Protooncogenes Genes that, if damaged, could
  result in cancer
• Tumor Supressor Genes Genes that hold suppress
  cell division
• P53 Protein factor that suppresses cell
  division in damaged cells, or caused apoptosis in
  heavily damaged cells

Check out these websites to learn more
The Eukaryotic Cell Cycle and Cancer CANCERQUEST