Cyclin activity

1. cyclin cyclin cyclin cyclin cyclin cyclin cyclin cyclin cyclin cyclin Cdk Cdk Cdk Cdk Cdk Cdk Cdk Cdk Cdk Cdk 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