Cell Cycle

• Cell cycle


  The regulated sequence of events that occurs between one cell division and the next
• Cell cycle


  1. Interphase

  2. Nuclear division (mitosis)

  3. Cell division (cytokinesis)
• The length of the cell cycle is very variable depending on environmental conditions, the cell type and the organism
• Interphase


  The cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis)
• Interphase


  1. G1 phase

  2. S phase

  3. G2 phase
• During the G1 phase a signal is received telling the cell to divide again
• The DNA in the nucleus replicates (resulting in each chromosome consisting of two identical sister chromatids) during the S phase
• G1 phase


  The gap between the previous cell division and the S phase, where the cell makes the RNA, enzymes and other proteins required for growth
• G2 phase


  The gap between the S phase and next cell division event, where the cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired
• Mitosis is part of a precisely controlled process known as the cell cycle
• Mitosis


  The nuclear division phase of the cell cycle
• Cytokinesis


  The cell division phase of the cell cycle, where the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells
• Regulation of the cell cycle

  • It is essential that the DNA within new cells is accurate in order for them to carry out their function
  • When the DNA is replicated (during the S phase) errors can occur
  • There are several checkpoints throughout the cell cycle where the genetic information contained within the replicated DNA is checked for any possible errors
  • Specific proof-reading enzymes and repair enzymes are involved in this checking process
  • When possible enzymes will repair the error but in some cases the cell may destroy itself to prevent passing on harmful mutations
• Checkpoints in the cell cycle

  • During G1 phase - chromosomes are checked for damage
  • During S phase - chromosomes are checked to ensure they have been replicated
  • During G2 phase - an additional check for DNA damage occurs after the DNA has been replicated
  • During metaphase - the final check determines whether the chromosomes are correctly attached to the spindle fibres prior to anaphase