The cell cycle control system
Connected series of biochemical switches. On/off type
3 major checkpoints
The cell cycle control system depends on cyclin-dependent protein kinases (Cdks)
Cyclins undergo a cycle of synthesis and degradation in each cell cycle.
Cdk levels stay constant.
3 cyclins are required in all eukaryotic cells.
Yeast: 1 Cdk, Vertebrate: 4 Cdks
Cdk activity can be suppressed by Cdk inhibitory proteins (CKI)
Help fine tune G 1S- and S-Cdks, in addition to cyclin synthesis/degradation (main
mechanism) and Cdk phosphorylation
The cell-cycle control system depends on cyclical proteolysis
Anaphase-promoting complex or cyclosome (APC/C), an ubiquitin ligase
SCF is also an ubiquitin ligase
The cell-cycle control system function as a network of biochemical switches
Each switch is influenced by various inhibitory mechanisms: information about
environment, cell damage, incomplete cell cycle events, etc.
S-Cdk initiates DNA replication once per cycle
The genome must be copied only