Briefly describe how the cell cycle is controlled and why phosphorylation of proteins plays a major role.

Concepts to Consider: The cell cycle is controlled through cell cycle checkpoints which ensure that certain criteria are met before the cell proceeds to the next cycle phase. Proteins that catalyze cell cycle events are either activated or inactivated by phosphorylation. Cyclin-dependent kinases (Cdks) control the phosphorylation of other proteins, allowing them to regulate the transitions between phases of the cell cycle.