CdK2 / cyclin B. The cell cycle is controlled by enzymes like cyclin dependent kinases (CdKs). CdKs phosphorylate amino acids like serine and threonine which initiates or blocks the activities related to cell cycle. The other check points involved in cell cycle are ·G1 checkpoint(Enter S or synthesis) is controlled by CdK4/ Cyclin D,CdK6 Cyclin D·G2 check point (Enter M or maturation promoting factor) is controlled by CdK2 / cyclin B. Metaphase check point is controlled by cyclin B degradation.