Short introduction to the cell cycle

Molecular pathways that regulate cell growth and differentiation are now beginning to be understood. This is mainly due to the identification of molecules that orchestrate the cell cycle. Cyclins and the cyclin-dependent kinases (CDKs) are the major players in the control of cell cycle progression. Cyclins do not have enzymatic activity and CDKs are inactive without a partner cyclin. The CDKs regulate the function of multiple proteins involved in DNA replication and mitosis by phosphorylating them at specific regulatory sites, activating some and inhibiting others to coordinate their activities. In this way cyclin/CDK complexes coordinate an ordered passage from a cell cycle phase to the next one. Multiple levels of regulation of cyclin/CDK complexes are present in “cell machinery” to obtain a tight control of cell cycle progression. In this chapter we will address these items