Cell Cycle
M phase – mitosis/cytokinesis
G0 phase – resting/ senescence
G1 phase – cellular growth, synthesis of mRNA, synthesis of proteins required for DNA synthesis e.g.
centrosomes
S phase – cellular growth continues as well as DNA, proteins and enzyme synthesis
G2 phase – organises and starts to condense genetic material, allows checking that all necessary
proteins and DNA have been synthesised
Check points
M phases CP – if all chromosomes are attached to spindles/ STOP if chromosomes are misaligned
- Inhibition of APC (Anaphase promoting complex) activation delays exit until complete
R CP (G1) – if environment is favourable enter S phase/STOP if DNA damaged
- Cdk inhibitors block entry to S phase, removed by mitogens
G2 CP – enter M phase if environment is favourable and all DNA is replicated/STOP if un-replicated
or damaged DNA
- Inhibition of phosphatase (cdc25) blocks entry to M phase if DNA replication still incomplete
Cyclin-cdk complex Cyclin Cdk partner
G1-cdk D1, D2, D3 Cdk4, cdk6
G1/s-cdk E Cdk2
S-cdk A Cdk2, cdk1
M-cdk (MPF) B Cdk1
MPF- maturation promoting factor – general regulator of G2-M, protein kinase
Inhibitors
Inhibitor Cdk-cyclin complex Cell cycle phase affected
Ink4 family (p15, p16, p18, p19) Cdk4, cdk6 G1
Cip/kip family (p21, p27, p37) Cdk1/cyclin A G2
Cdk1/cyclin B G2/M
Cdk2/cyclin A S
Cdk2/cyclin E G1
M phase – mitosis/cytokinesis
G0 phase – resting/ senescence
G1 phase – cellular growth, synthesis of mRNA, synthesis of proteins required for DNA synthesis e.g.
centrosomes
S phase – cellular growth continues as well as DNA, proteins and enzyme synthesis
G2 phase – organises and starts to condense genetic material, allows checking that all necessary
proteins and DNA have been synthesised
Check points
M phases CP – if all chromosomes are attached to spindles/ STOP if chromosomes are misaligned
- Inhibition of APC (Anaphase promoting complex) activation delays exit until complete
R CP (G1) – if environment is favourable enter S phase/STOP if DNA damaged
- Cdk inhibitors block entry to S phase, removed by mitogens
G2 CP – enter M phase if environment is favourable and all DNA is replicated/STOP if un-replicated
or damaged DNA
- Inhibition of phosphatase (cdc25) blocks entry to M phase if DNA replication still incomplete
Cyclin-cdk complex Cyclin Cdk partner
G1-cdk D1, D2, D3 Cdk4, cdk6
G1/s-cdk E Cdk2
S-cdk A Cdk2, cdk1
M-cdk (MPF) B Cdk1
MPF- maturation promoting factor – general regulator of G2-M, protein kinase
Inhibitors
Inhibitor Cdk-cyclin complex Cell cycle phase affected
Ink4 family (p15, p16, p18, p19) Cdk4, cdk6 G1
Cip/kip family (p21, p27, p37) Cdk1/cyclin A G2
Cdk1/cyclin B G2/M
Cdk2/cyclin A S
Cdk2/cyclin E G1
