|MoBio||Cell Cycle||Chapter 8|
The cell cycle is a series of events that lead to cell division. It consists of four phases: G1, S, G2 and M, where "G" stands for "gap", "S" represents "synthesis" and "M" means "mitosis". A newly divided cell may either enter into another round of cell division or remain in the resting state for a long period of time. In the latter case, the cell is said to be in the G0 phase. Upon specific stimulation, cells in the G0 phase may re-enter the G1 phase.
CDK and Cyclins
The progression of a cell cycle is catalyzed by cyclin-dependent kinase (CDK) which, as the name suggests, is activated by a special class of proteins called cyclins. In mammals, different cyclins are designated as A, B, C, D and so on. In budding yeast (S. cerevisiae), nine cyclins have been identified: Cln1 to Cln3 and Clb1 to Clb6.
The proteins of the CDK superfamily in mammals is denoted by Cdk followed by a number. However, in yeast, they are denoted by Cdc (cell division control) and a number. Among them, Cdc2 was first identified in fission yeast ( S. pombe). It is equivalent to Cdc28 in budding yeast, and to Cdk1 in mammals. Cdk1 is often referred to as Cdc2.