Control of the cell cycle Flashcards
there are two irreversible points in cell cycle
Replication of DNA
Separation of sister chromatids
checkpoints
see slide 23-26
Allows cell cycle to respond to internal state of cell and integrity of genetic material
Allows cell cycle to respond to environmental signals
name checkpoints
G1 transition
G2/M transition
metaphase to anaphase transition
What happens once you pass the G1 transition
commit to cell cycle and dna replication
what does the G1 transition check for in order for cell to proceed to delay or divide
Cell size
Nutrients
Growth factors (environment ok?)
DNA damage
What happens at the G2/M transition
Cell size
DNA replication
DNA damage
is cell ready for mitosis
what happens at the metaphase-anaphase transition
spindle assembly check
chromosome alignment and connected to spindle
to proceed with mitosis
Cyclin-dependent kinases (Cdks)
central component of cell cycle control
what does the activity of the cdks depend on
where in cell cycle it is
name 2 key components of cell cycle
slide 27
protein kinase
cyclins
protein kinase
when cdk binds with cyclin it forms protein kinase
no cyclin inactive
cyclin
Proteins that undergo process of synthesis and degradation each cell cycle
Direct Cdk to specific target proteins at different times during cell cycle
4 classes of cdks
see slide 28 graph
G1/S cyclin
S cyclin
M cyclin
G1 cyclin
G1/S cyclin
Activate Cdk in late G1
Trigger progression through Start or Restriction point
Levels fall in S phase
S cyclin
Bind Cdks after Start or Restriction point
Stimulate chromosome duplication (DNA replication)
M cyclin
Stimulate entry into mitosis
Levels fall in mid-mitosis
G1 cyclin
Help govern activities of G1/S cyclins
How is cdk fully activated
Cdk-activating kinase (CAK)
How does cdk activate at t loop
see slide 29
T loop partially blocks Cdk active site (B) = partially active
Phosphorylation at T loop frees Cdk active site (C) = fully active
when is cdk not active
no cyclin attached
Cyclin-Cdk complex inhibited by:
Phosphorylation by Wee1 kinase
Binding of Cdk inhibitor proteins (CKIs)
Phosphorylation of Wee1 kinase does
controls m-cdk activity
Binding of Cdk inhibitor proteins (CKIs)
Governs G1/S- and S-Cdks
what is an Anaphase-promoting complex
cyclosome (APC/C)
cyclosome
Member of ubiquitin ligase family of enzymes
Catalyzes ubiquitylation and destruction of two major types of proteins
when is cyclosome active
Remains active during G1
Turned off when G1/S-Cdk is activated
2 types of cyclosome
securin
G1/S cdk
what does securin do
Protects protein linkages holding sister chromatids in early mitosis
When destroyed, activates protease that separates sister chromatids (anaphase)
what do G1/S cdk do
Destruction inactivates most Cdks
Dephosphorylation of Cdk targets required for completion of mitosis
look at slide 31
confusing may need to ask question to him
slide 31
