<P> Within the cell cycle, there is a stringent set of regulations known as the cell cycle control system that controls the timing and coordination of the phases to ensure a correct order of events . Biochemical triggers known as cyclin - dependent kinases (Cdks) switch on cell cycles events at the corrected time and in the correct order to prevent any mistakes . </P> <P> There are three checkpoints in the cell cycle: the G / S Checkpoint or the Start checkpoint in yeast; the G / M checkpoint; and the spindle checkpoint . </P> <P> During G phase, the G / S cyclin activity rises significantly near the end of the G phase . </P> <P> Complexes of cyclin that are active during other phases of the cell cycle are kept inactivated to prevent any cell - cycle events from occurring out of order . Three methods of preventing Cdk activity are found in G phase: inhibitory gene regulatory proteins suppress major cyclin genes from expression (* the way this is phrased it is unclear whether it is transcription of the gene or translation of the mRNA gene product that is being regulated); anaphase - promoting complex (APC) is activated, which targets and degrades S and M cyclins (but not G / S cyclins); and a high concentration of Cdk inhibitors is found during G phase . </P>

When does the cell commit to go through cycle