1
Q
G1 checkpoint
A
- Regulates transition from G1-to-S phase
- Monitors environment before allowing cell cycle to progress
2
Q
G2 checkpoint
A
- Regulates transition from G2-to-M phase
- Monitors DNA for proper replication & environment
3
Q
M-phase checkpoint
A
- Spindle assembly checkpoint (SAC)
- Regulates transition between metaphase & anaphase
- Monitors chromosomes for proper attachment at metaphase plate
4
Q
Mitogens
A
- Stimulate cell to initiate cell division
- Sets off signal transduction pathway letting cell know to start process of growth & division
5
Q
Rb
A
- Suppress expression of genes whose proteins are needed for S phase
- Rb-dependent suppression of gene expression must be relieved for cells to commit to entering S phase & rest of cell cycle
- Once these proteins are synthesised the cell is committed to progressing to S phase & growth factors no longer needed
6
Q
ATM & ATR
A
- Activated by DNA damage
- Phosphorylate downstream kinases that phosphorylate p53 & stabilise it
7
Q
p53
A
- Phosphorylated by ATM & ATR
- When phosphorylated, can induce expression of proteins p21 & Puma
- Inactivated by many different types of cancer
8
Q
p21
A
- Expression induced by phosphorylated p53
- Binds to & inhibits complexes of cyclin-Cdk. In G1 this prevents inactivation of Rb & the cell remains in G1
9
Q
Puma
A
- Expression induced by phosphorylated p53
- Inhibits Bcl2: A key protein required for inhibition of cell death. This prolonged & irreperable DNA damage induces cell death
10
Q
Geminin
A
- Ensures cell only undergoes one cycle of DNA replication
- Expression of Geminin begins at S phase
- Binds to Cdt1 & prevents it from forming new pre-replication complexes
- Geminin degraded during anaphase, allowing Cdt1 to participate in another round of DNA replication
11
Q
Cdt1 & MCM
A
- Required for DNA replication
- Help form pre-replication complex
12
Q
Cdc20
A
- Associates with anaphase promoting complex / cyclosome (APC / C) to form functional ubiquitin ligase
13
Q
APC / C
A
- Anaphase promoting complex / cyclosome
- Associates with Cdc20 to form functional ubiquitin ligase
- One target is cyclin B, deactivating it
14
Q
Ubiquitin ligase
A
- Adds small protein (76 amino acids) called ubiquitin to proteins & targets them for proteolysis (degradation)
15
Q
Securin
A
- Target of APC / C, degrading it
- Binds to separase enzyme that degrades cohesin
- When bound, separase is inactive & sister chromatids remain attached
16
Q
Separase
A
- Binds to securin
- When bound, separase is inactive & sister chromatids remain attached
17
Q
Mad2
A
- Can exist in either closed or open form
- In closed form it can bind to & inhibit Cdc20
- Converts into closed form by associating with kinetochore-bound Mad1
- Even 1 unattached kinetochore sufficient to produce enough closed Mad2 to inhibit all cellular Cdc20 & prevent anaphase
