Cell

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• Cell Molecular Biology
• Control of the Cell Cycle

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M-checkpoint

• G2 Checkpoint
• Controls entry to mitosis
• DNA replication assessed
• Full genome must be present to allow copy for
  each daughter cell

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• G1 checkpoint
• Multicellular organisms, signalling molecules
  called growth factors from surrounding cells
  trigger the production of cyclins which increase
  in concentration at the checkpoints.
• Cyclins bind to kinase enzymes known as cyclin
  dependent kinases (CdK) forming cyclin-CdK
  complex
• Cyclin-Cdk complex activates key proteins by
  phosphorylation

Growth factors
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Control of G2 checkpoint

• G2 cyclin levels build up and bind to kinase
  enzymes (CdK)
• CdK plus M2 cyclin forms active protein complex
  called mitosis promoting factor or MPF.
• Mitosis Promoting Factor is essential for entry
  to mitosis.

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• Progression beyond G2 checkpoint involves
  activation of cyclin dependent kinase (Cdk)
• by G2 cyclins.
• Complex is called Mitosis Promoting Factor (MPF)
• Increased concentration of MPF causes
• chromosomes to condense
• Nuclear membrane breakdown
• Mitotic spindles form and chromosomes move to the
  equator

The concentration of MPK does not change but its
activity rises and falls to to changes in the
levels of G2 cyclin. Click here for animation
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M (metaphase) checkpoint

• Controls entry to anaphase
• Ensures chromosomes are aligned correctly on
  equator
• Ensures daughter cells receive correct number of
  chromosomes
• Triggers separation of daughter chromosomes and
  then cytokinesis

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Abnormal Cell Division Cancer The cell cycle is
under genetic control. There are two groups of
genes involves Proliferation
Anti-proliferation Genes
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Proliferation Genes

• Proliferation genes or proto-oncogenes These
  switch on the process of mitosis by coding for
  proteins that promote cell division e.g. MPF
• These are dominant genes therefore a single
  mutation would convert them into the mutant type
  oncogenes, starting uncontrolled cell division
• Oncogenes are mutated genes where there is a
  gain-of-function
• Oncogenes promote cell division by the
  overproduction of a stimulatory protein such
  mutations can be at any level in signalling and
  transduction.

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Anti-proliferation Genes

• These are also known as tumour suppressor genes
  or anti-oncogenes and are involved in restricting
  cell division
• Eg. p53 gene, act at checkpoints by generating
  proteins that block progress through the cell
  cycle when conditions are not met.
• When tumour suppressor genes mutate there is
  loss-of-function allowing damaged or unrepaired
  cells to divide
• Two copies of the antiproliferation gene have
  to mutate before a tumour starts to develop as
  they are recessive in nature
• For nice game on cell cycle click here

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• Essay question due Friday
• Write notes on cell cycle and control under the
  following headings.
• Interphase (5)
• Mitosis (5)
• Mutations (5)