Cell growth + division Catherine Flashcards
1
Q
Transcriptional activation of cell cycle
A
- +ve feedback (move to next stage and repress previous)
- pRb binds E2F to repress expression in G1, Cyclin D-Cdk4/6 phosph pRb
- E2F induces cyclin E expression → cyclin E further phosph pRb → transcribes cyclin A
- Cyclin A = -ve feedback, phosph E2F
2
Q
Degradation of mitotic proteins
A
- SCF
- Controls G1/S and G2/M boundaries
- SCF substrates = cyclin D/E + CKIs like p27 - APC
- Co-activators = Cdc20 + cdh1
- Activated cyclin B → activated Cdc20
- If free kinetochores, APC/C is inhibited by MCC
- MCC turned over by TRIP13 → free APC
- When kinetochores are attached to microtubules, ↓ formation of MCC but turnover of TRP13 carries on, ↓ inhibition on APC/C
- Cyclin B then degraded
3
Q
Regulation of proteolysis machinery
A
- APC/C needs Cdc20/Cdh1 to bind
- In early M, CDK phosph APC/C → Cdc20 binds → cyclins destroyed → ↓ CDK → anaphase
- Cdh1 is phosphorylated during S, G2 + M, x bind APC
- When exits M, Cdh1 is dephosph to activate APC. This ubiquit Cdc20 so x simultaneous activation of both
4
Q
CKIs
A
Yeast
- Sic1p phosph Cdc28-cyclin, prevents premature S phase entry
Mammals
- INK4 + CIP/KIP
- p27 highest in Go + early G1, ↓ ↓ in G1/S
- Prevent activation of cyclinE-Cdk2 or cyclinD-Cdk4
- E2F → p27 transcription → cyclin E/ cdk2 inhibited → x pRb phosph (-ve feedback)
5
Q
Regulation by phosphorylation
A
- Cdc2 = inhibited at Thr14/Tyr-15 + activated at Thr161
- Wee1/Cdc25
- CAK = activating phosph
- Cdk1 activates own activator Cdc25 + inhibits inhibitor, w/o cyclin B Cdk1 ↓, wee1 ↑ cdc25 ↓
6
Q
DNA replication control
A
- CDT1 needs to be free + dephosph
- Geminin sequesters CDT1 but destroyed by APC in A
- Cdt1 removed during DNA replication so PIC x re-assemble
7
Q
GFR as oncogene more
A
- Ligand binds to ectodomain → dimerisation → activates IC tyr kinase domain
- Phosphotyr activates ds components
- Point mutation to one that causes dimerisation + activated w/o ligand
- Or chromosomal translocation, replaces EC domain w/ segment that dimerises
8
Q
Intracellular transducer as oncogenes more
A
- Ras mutations in Q61, G12 + G13
- Q61 interfers w/ H20 coordination needed for nucleophilic attack
- G12/G13 prevent van der waal btw Ras + GAP through steric hindrance which affects orientation of catalytic Gly at 61
- Raf becomes oncogenic by mutation at Val600→ Glu600 (mimics activation loop)
9
Q
TF as oncogenes more
A
- Ras affects myc expression in 2 ways
1. P13K = ds of Ras, inhibits GSK3 → prevents Myc being proteolysed
2. Ras activates Raf-1 → activates MEK pathway → phosph of c-Myc - Myc = 40% of tumours
- ↑ effects e.g. cyclin D, CDKs (activates Cdc25), E2F (myc stimulates CDK → phosph pRb → frees E2F, directly w/ E2F promoter) + CKIs
10
Q
Oncogenes not involved in cell proliferation
A
- Bcl-2 inhibits apoptosis
- Tumour suppressors = also important e.g. p53
- Telomerase + VEGF also oncogenes
- Protein acts is important e.g. at branch vs in linear pathway
+ how easy to mutate
11
Q
p53 vs pRb
Activation
A
- p53 = phosph + stabilised by several kinases, Mdm2, ARF
- pRb = phosph
12
Q
p53 vs pRb
Effects - cell cycle
A
- pRb acts through E2F target genes, p53 acts directly via p53 target genes
- pRb binds E2F and blocks transcription (can repair damage)
- p53 acts through p21 (inhibit Cdk2, prevents inactivation by Prb)
- p21 null mice are deficient in cell cycle arrest
13
Q
p53 vs pRb
Effects - CIN
A
- Experiments knockout
- BubR1 can physically assoc. w/ + activate -53 during SAC checkpoint activation + p53 activates BUBR1
- pRb loss affects mitotic fidelity
14
Q
p53 vs pRb
Effects - Apoptosis
A
- Extrinsic
- Phosph pRb means genes like caspase 7 are expressed
- p53 induces expression of Fas TNF receptor - Intrinsic
- pRb induces MOMP by binding BAX
- p53 induces expression of pro-apoptic genes
15
Q
p53 vs pRb
Effects - metabolism
A
- E2F null mice
- p53 suppresses glucose transport directly by preventing GLUT1/4 transcription
- Oxidative metabolism
