Chromatin

Question 1

difference between active and open chromatin?

Answer 1

active –> expression occurring

open - TFs & RNA polymerase has access to DNA

Question 2

what can’t be modified?

Answer 2

H1

Question 3

what residues are methylated?

Answer 3

Lys & Arg
active = H3 Lys 3 (trithorax gp)
inactive = H3 Lys 9 (polycomb proteins)
HP1 binds methylated lys 9 –> condenses chromatin

Question 4

How is DNA methylated?

Answer 4

cytosine –> 5methyl cytosine
methylated DAN binds MeCP2
MeCP2 recruits HDAC, leading to inactive chromatin

Question 5

difference between eu and heterochromatin?

Answer 5

eu is less condensed & active
hetero is condensed & inactive
both in interphase nuclei

Question 6

What part of histones are modified?

Answer 6

N-terminal tail
Extends beyond nucleosome and can affect DNA interaction with regulatory proteins OR with DNA OR with histones in adjacent nucleosomes.

Of H2A, B, 3 or 4.

Question 7

What is the ‘histone code’?

Answer 7

Modification pattern of histones is duplicated during replication.

Question 8

What final way can histones be modified?

Answer 8

H3 variant, CENP-A (46% identity to H3 involved in organising chromatin at centromere