Cell growth + division lecture 3 Flashcards
1
Q
Chromosome structure
A
- Loop scaffold model
- 20,000 fold compaction
2
Q
Nucleosomes
A
- Formed from 2 copies of 4 histone proteins
- 147 bp periodicity
3
Q
Histone tail modification
A
- H H4 lys-rich tail
- H H3 phosph on T3 by haspin kinase → Aurora B kinase recruited → phosphate H H3 on Ser10
- Δ charge by acetylation/phopsph → Δ compaction
4
Q
Chromosome scaffold
A
- Diffraction pattern of interphase nuclei show periodicity in reflections (2,11,30-40nm)
- Cryo-EM = chromatin disordered
5
Q
Do you need histones to make chromosomes
A
- Xenopus egg extract depleted of histone H1
- Still form chromosomes
6
Q
What is needed for chromosome condensation
A
- SMC1 = 1st SMC found by genetic screen
- Mutant x segregate DNA
7
Q
SMC function
A
- SMC1 + 3 = cohesin
- SMC1 + 3 = linked by regulatory subunit, rapidly binds + releases DNA
- Smc3 acetylation blocks wap1 release (S phase)
- Sororin inactivation by mitotic kinase → cohesin release
8
Q
Centromere
A
- Here, CENPA replaces H H3
- Also recruits that protect cohesion from kinases (Sgo1, PP2A)
- In P, arms of chromatid held as have cohesin
- Phosph by Cdk1/aurora B releases cohesin
- x happen at centromere as have PP2A
9
Q
Cohesin release
A
- Separase = protease for Scc1 of cohesin
- 2 regulatory partners (cyclin B + securin, inhibit)
- Once spindle checkpoint is satisfied, MPS1 forms MCC, inhibits APC
- When all kinetochores attached, TRP13 recycles Mad2, APC = active
- APC breaks down cyclin B + securing → separase x inhibited cohesin destroyed
10
Q
Condensin
A
- Made up of SMC2 + 4
- Sequentially condense chromosome
- In M, associates w/ DNA + extrudes loops of DNA through ring, makes DNA shorter
- Condensin 1 = 1st, CDK1
- Condensin II = 2nd, makes smaller loops
11
Q
High resolution analysis of chromosome structure
A
- Hi-C
- TADd lost at G2/M, replaced by diagonal band
- Remove condensin + see effects
