Cell cycle is run by a group of special proteins like

Cell cycle is run by a group of special proteins "Cyclins and Cdks. 
The regulatory molecules that control the cell cycle are mainly proteins of two types: protein kinases and cyclins. Protein kinases are enzymes that activate or inactivate other proteins by phosphorylating them. To be active, such a kinase must be attached to a cyclin, a protein that gets its name from its cyclically fluctuating concentration in the cell. Because of this requirement, these kinases are called cyclin-dependent kinases, or Cdks