Search

Normal regulation of the cell cycle ensures the passage of genetic material without mutations and aberrations. Proper completion of each phase is critical to the initiation of the following phase, and the pathways that cell division occur in an ordered, sequential, and irreversible procession. The two major cell-cycle events that are regulated tightly are DNA replication and cell division. Progression through each phase transition is regulated by extracellular signaling, transcription factors, cyclin-dependent kinases (CDKs), and checkpoints, which prevent uncontrolled cell division. Cyclin/CDK complexes are the primary factors responsible for the timely order of cell-cycle progression, which include entry into S phase, initiation of DNA replication, and mitotic entry. Each phase of the cell cycle and the different cyclin/CDK complexes, as well as other important factors that regulate cell-cycle progression and checkpoints, will be discussed.