Cell Cycle

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The cell cycle is an ordered set of events that culminates in cell growth and division into two daughter cells

It can roughly be divided into two main stages:


Interphase

  • The stage in the development of the cell between two successive M phases
  • This phase of the cell cycle is a continuum of 3 distinct stages (G1, S, G2), whereby the cell grows and matures (G1), copies its DNA (S) and prepares for division (G2)
  • Sometimes cells will leave the cell cycle and enter into a quiescent state (G0), whereby it becomes amitotic and no longer divides


M phase

  • The periods of nuclear division (mitosis) and cytoplasmic division (cytokinesis)


                                             The Cell Cycle                                                                                                                 M Phase


Interphase

Interphase is an active period in the life of a cell - many events need to occur before a cell can successfully undergo division:

  • Protein synthesis:  The cell needs to synthesise key proteins and enzymes to enable it to grow, copy its contents and then divide
  • ATP production:  The cell will need to generate sufficient quantities of ATP in order to successfully divide
  • Increase number of organelles:  The cell needs to ensure both daughter cells will have the necessary numbers of organelles needed to survive
  • DNA replication:  The genetic material must be faithfully duplicated before division (this occurs during the S phase)


As none of these processes can occur during the M phase, interphase contains growth checkpoints to ensure division is viable

  • G1:  A checkpoint stage before DNA replication during which the cell grows, duplicates organelles, synthesises proteins and produces ATP
  • S:  The stage during which DNA is replicated
  • G2 A checkpoint stage before division during which the copied DNA is checked for fidelity (mutations) and final metabolic reactions occur


DNA Replication

  • During interphase (the S phase) the DNA is replicated to produce two copies of genetic material
  • These two identical DNA molecules are identified as sister chromatids and are held together by a single centromere
  • During the events of mitosis, the sister chromatids are separated and drawn to opposite poles of the cell (becoming separate chromosomes in the process)
  • When the cell divides into two, the two resulting nuclei will each contain one of each chromatid pair and thus be genetically identical 


Cancer

  • The cell cycle is controlled by a complex chemical control system that responds to signals both inside and outside of the cell
  • Tumor suppressor genes produce proteins which inhibit cell division, while proto-oncogenes produce proteins that promote growth and division
  • Mutations to these genes result in uncontrolled cell division, resulting in the formation of a tumour
  • Tumours can grow in size which causes damage local tissue; they may also spread to other parts of the body (malignant tumours)
  • Diseases caused by the growth of tumours are collectively known as cancers


Cancer in Tasmanian Devils