1. Cyclin activity time Cdk cyclin Cdk cyclin Cdk cyclin Cdk cyclin Cdk
Cyclins continue
to accumulate
Cdk
Cyclins produced
by gene expression
Cdk
cyclin
Cdk
cyclin
Cyclins rapidly degraded
Cdk
Cdk
Cdk
Cdk
Cdk
cyclin
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