Cell growth + division lecture 1

Question 1

Stages of cell cycle

Answer 1

• G1, S, G2, M
• Microscopy = useful for describing events
• Yeast = genetic / mechanistic info

Question 2

Experiment

Order of cell cycle

Answer 2

• Fused G1 + S w/ virus induced fusion
• G1 immediately replicated DNA
• S phase has factor that triggered DNA replication
• Fused G2 + S
• G2 x replicate its DNA
• Fused G1, S or G2 to M2 → entry into mitosis so M has dominant activity

Question 3

Experiment

Control of cell cycle

Answer 3

• Temp sensitive mutant of CDC (grow at ↓ not ↑ temp)

- Find what complements cdc mutant

Question 4

Experiment

Rate limiting component of cell cycle

Answer 4

• Fission yeast cells add to end
• Mutants that divide at smaller size
• I mutant = wee1, entered S phase but M prematurely (x 2nd growth)

Question 5

Activation of CDKs

Answer 5

• Need cyclins + to be phosphorylation
• Phosph on T161 by CAK (activates)
• Phosph on T15/Y14 by wee1 (inhibits), cdc25 reverses
• CyclinB-CDK1 assembled + immediately inhibited in G2

Question 6

Cdc25/Wee1 regulation

Answer 6

• CyclinB-CDK1 ↑ during G2
• Threshold in late G2, phosph. Cdc25 (activates) + phosph. (inhibits)
• When cell exits = reversed
• Rapid change

Question 7

Cyclin degradation

Answer 7

• Mutagenesis showed 1st 90 aa of cyclinB has D-box, recognised by ubiquitin
• Ubiquitin recognised by proteasome

Question 8

APC/C

Answer 8

• In M, APC/C active via phosphorylation by Cdc20
• Immediately inhib. by MAD/Bub until chromosomes aligned
• Then cyclin-B destroyed