15. Regulation Of The Cell Cycle In G1,S Flashcards
G1 phase roll
Transcriptional reprogramming and intense protein synthesis, preparing to replicate
S phase roll
Doubling of 23 pair chromosomes
G2 phase roll
Restricting mitosis until DNA is doubled completely and cell becomes big enough
M phase roll
Mitosis (prophase, prometaphase, metaphase, anaphase, telophase)
Difference between Quiescent G0 and Senescent G0
Quiescent G0 is reversible and can be forced to proliferate
Senescent G0 is irreversible and will not go back into cycle
*depends on the cell type
Hayflick-phenomenon
After 40~60 mitosis, the cell division is forced to stop (senescence) and Telomerase induces to proliferate again by extending telomere in embryo and cancerous cell
4 options for the cell to take in life
- Proliferation
- Differentiation
- Apoptosis
- Remain undifferentiated
These stages are balanced in healthy human cell
Cdk-cyclin pairs in different phases
Kinase Cyclin
G1 Cdk4,6. D
G1/S Cdk 2. E
S Cdk 2. A(SPF)
G2/M,M Cdk 1(cdc2) B(MPF; M Phase promoting Factor)
All Cdk 7. H(CAK; Cdk Activating Kinase)
Determinants of Cdk activity
- Activating cofactor of cyclin
- CKI (Cdk Inhibitor prot)
- Activating phosphorylation (by CAK; Cdk7+cyclin H) on Thr
- Inhibitory phosphorylations (e.g. by Wee1) on Thr, Tyr
* inhibition is alwasy dominant
Cycle independent function of CAK in G0 phase
subunit of TFIIH
Highly conserved phosphatase which mediates deposphorylation the Tyr site phosphrylated by Wee1(Protein Tyr kinase)
Cdc25
what happen to the yeast cell if Cdc25 is hyperactive and Wee1 deficient
Due to hyperactive Cdk1-cyclinB, G2 gets too short and starts mitosis earlier. This results to smaller cell than normal
*It’s possible that No Cdk-cyclin complex controlling G2 phase
Two CKI family and the significance of it and how to function
CIP/KIP can interupt all phase and INK4 only deal with the G1 phase cyclin-cdk complex.
As binding CKI, cyclin-cdk complex occurs rearrangement in the Cdk active site which renders inactive.
Specific CKI which intervenes when DNA damage ocur
p21(CIP/WAF1) a.k.a. Cyclin dependent Kinase Inhibitor 1
Main steps of the cell cycle and conclusion with respect to cyclin, cdk, CKI, transcription factor
- Growth factor (Mitogen) binding to RTK
- MAPK, Akt/PKB cascase
- Reprogramming of gene transcription
- Cyclin D, Cdk4,6 , E2F increase, CKI(INK4) decrease
* it’s called mitogenic effect of GF
After overcome restriction point through Cdk4,6-cyclin D complex, Cdk4,6 and Cdk2 activates which factor?
They activate E2F by phosphorylation of pRB(RetinoBlastoma prot.) and pRB detaches from E2F and starts transcription for genes for S phase
Genes under the control of E2F
- ORC (Origin Recognition Complex) subunit
- MCM 2~7 (helicase complex)
- Cdc6, cdt1 (managing the assembly and binding of MCM complex)
- DNA polymerase alpha
- PCNA (Proliferating Cell Nuclear Antigen) which is sliding clamp for DNA pol delta/epsilon
- proteins for further progress of the cycle (e.g. cdc25)
- TF (e.g. E2F)
Mechanism to enter S phase
Increased conc. Of Cdk2-Cyclin E complex phosphorylates CKI(p27) so that it is ubiquitinated from Cdk2-Cyclin A(SPF) then this activates pre-replication complex via phosphorylating MCM2~7, Cdc6, cdt1 to form and activate the helicase.
Meaning of Reprogramming transcription
Phenomenon of global change in gene expression that are typically initiated by transcriptional factors
Description the process from pre-replication complex to DNA replication
- From pre-replication complex (MCM2~7, ORC with cdc6, cdt1), SPF phosphorylate MCM2~7, cdc6, cdt1 and activate the complex.
- After ORC complex with cdc6, cdt1 is replaced by helicase activator and SSBP, DNA is unwinded
- DNA pol. Alpha, primase, dNTP and NTPs are added and DNA replication occurs
cdc25 and Wee 1 different identity and thier functional meachanism
cdc25 is phosphatase which will be active when it’s phophorylated
Wee 1 is kinase which will be active when it’s dephosphorylated
Both of them are turned off and on by PP which is inhibited by active CDK
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