8 - Histones and Packaging

Question 1

hierarchy of dna packaging?

Answer 1

nucleosome
chromatin
chromosome

Question 2

both types of histone families?

Answer 2

linker
- h1

core

• h2a
• h2b
• h3
• h4

Question 3

what makes up chromatin?

Answer 3

a nucleosome [dna around a histone]

nucleosome has 2x each histone

Question 4

how is a nucleosome formed?

Answer 4

H3/4 dimerization

• h3 and h4 bind to form a histone handshake [heterodimer]
• as theres 2 of each, two dimers form
• both dimers form a bond in middle
• tetramer

H2A/B

• h2a and h2b form a dimer [weak as less conserved]
• 2 H2A/B dimers
• bind to both H3/4 dimers
• octomeric core

Question 5

h2 variants?

Answer 5

H2Z
H2X
H2 BBD
macro H2A

Question 6

5 h3 variants?

Answer 6

H3.1
H3.2
H3.3
H3.it
CenpA

Question 7

steps of dna packaging?

Answer 7

1. nucleosome
2. 10nm fibre
   - chain of nucleosomes
   - dna accessible joined by linkner dna
3. 30nm solenoid
   - 6th nucleosome forms circle
   - held by H1 linkers
4. 300nm solenoid
   - loops of 30nm solenoids held by non-histone scaffold proteins
5. 700 nm fibre
   - coiled coil
   - tightly packaged
6. chromosome
   highest condended form