Checkpoints

Checkpoints are used by the cell to monitor and regulate the progress of the cell cycle. If a cell fails to meet the requirements of a phase it will not be allowed to proceed to the next phase until the requirements have been met. Several checkpoints are designed to ensure that damaged or incomplete DNA is not passed on to daughter cells. At the end of the G1 phase, G2 phase and after DNA has been replicated in the S phase it is checked for damages. At the end of the M phase a checkpoint is present to stop cytokinesis in case the chromosomes are not properly aligned on the mitotic spindle.

Synchronisation of Cell Cultures

Several methods can be used to synchronise cell cultures:
Serum starvation - G1 phase
Mitotic shake-off - M phase
Treatment with colchicine - M phase
Treatment with 5-fluorodeoxyuridine - S phase

Observation

There are numerous ways to observe the cell cycle occurring. Normally onion bulbs or garlic root tips are used. A sample of root tip is fixed in a mixture of 99% of 70% aqueous industrial methylated spirit and 1% glacial ethanoic acid for two hours. Treat the root tips in 1M hydrochrolic acid at 60C for 6 -7 minutes. Rinse thoroughly with water. Add Schiff’s reagent and leave for one hour. Rinse again in distilled water. Observe under a microscope.