Cyclin activity

1
Cyclins continue to accumulate
Cdk
Cyclins produced by gene expression
Cyclins rapidly degraded
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cdk
Cyclin activity
Cdk
Cdk
Cdk
Cdk
Cdk
time
Cdks not active Substrates not
phosphorylated SCF not active Cyclins not
destroyed and accumulate due to
transcription/translation
Some cdks active Some phosphorylation Cell begins
preparing for S phase Some substrates
phosphorylated Some SCF active, but not
enough to stop process
Most cdks active Lots of phosphorylation Cell
enters S phase Substrates phosphorylated at a
rapid rate Cyclin production remains
normal SCF very active and rapidly begins
ubiquitinating cyclins Ubiquitination
targets cyclins for destruction Rate of
cyclin destruction higher than cyclin
production
Cyclins are destroyed faster than they are
produced Cdks become inactive and no longer
phosporylate substrates SCF degrades naturally
and new SCF molecules are not
phosporylated (inactive) With no active SCF,
cyclins begin to build up again