Cell Checkpoints

Cell cycle checkpoints are mechanisms that ensure the fidelity and continued viability of mitotic division in cells

Multiple checkpoints have been discovered, each with different specific roles:

G1 Checkpoint:

  • Determine appropriate growth conditions (sufficient nutrients, cell size, presence of growth factors, etc.)
  • Assess level of DNA damage (from ionising radiation or UV) 

G2 Checkpoint:

  • Determine state of pre-mitotic cell (suitable cell size required for successful division)
  • Identify an replication faults (changes to DNA sequence will distort genetic fidelity in daughter cells)

Metaphase Checkpoint:

  • Ensure proper spindle assembly and correct attachment to centromeres (prevents non-disjunction events)

Cell Cycle Checkpoints

cell checkpoints

G0 Stage

Not all cells are continually replicating – some cells may enter into a non-dividing G0 stage

These cells may either be dormant (quiescent) or ageing and deteriorating (senescent)

Cells enter the G0 phase from the G1 phase; quiescent cells may re-enter G1 at a later time (senescent cells do not)

Normally, cells will only divide a finite time before reaching senescence (a typical human cell will divide ~ 40 - 60 times)

Specialised cells will often permanently enter G0, as differentiation has prevented their capacity for further division  

Neurons are examples of cells that have been arrested in a G0 state – these cells are amitotic (cannot divide)