Revised notes: R-point is controlled by Retinoblastoma protein Flashcards
1
Q
How is the R-point controlled by the Rb? (2)
A
- During the R point, E2F TFs are inactive as they are locked to hyper-phosphorylated RB
- This prevents E2Fs from expressing the required cyclins for cell cycle development
2
Q
How does mitogenic signalling allow passing of R point? (7)
A
- Mitogen signalling activate TFs such as AP-1
- AP-1 binds to DNA and codes for cyclin D mRNA
- Cyclin D mRNA is translated to produce cyclin D
- Cyclin D binds and activates Cdk4/6
- D-Cdk4/6 phosphorylates Rb, inactivating it, and causes it to release its inhibition on E2F
- E2F is now active and induces gene expression of cyclin E and other cyclins
- Cyclin E/Cdk2 hyper-phosphorylates Rb and completely inactivates it
3
Q
What occurs during G2 phase?
A
Cyclin B-Cdk1 is formed and allows cells to progress to M phase
4
Q
What occurs during the prophase and prometaphase?
A
- Cyclin B-Cdk1 phosphorylates proteins which results in condensing of DNA, formation of the mitotic spindle and breakdown of the nuclear envelope
- Chromosome segregation requires correct attachment of sister chromatids to the spindle
5
Q
What occurs during metaphase?
A
After attachment, the chromosomes are tugged between the two poles, resulting in them moving to the spindle equator
- Unattached kinetochores to the spindle are detected by the spindle assembly checkpoint which blocks entry to anaphase - Incorrect kinetochore attachment requires correction which causes chromosomes to lag in the spindle, incurring damage later
6
Q
What occurs during anaphase and telophase?
A
Separation of chromatids:
- The pull on kinetochores by the spindle is resisted by the cohesion of the chromatids
- Chromatids are connected by cohesin proteins
- Cyclin B-Cdk1 triggers the steps to cause breakdown of cohesin
7
Q
What happens when Cyclin B-Cdk1 deactivates?
A
- Spindle disassembly
- Reformation of nuclear envelope
- Division of cytoplasm into two cells
