Nucleosomes, chromatin and chromosome structure

Question 1

What histones form the nucleosome?

Answer 1

H2a, H2b, H3, H4. 2 of each to form an octamer.

Question 2

What is H1?

Answer 2

H1 is a linker histone and is NOT involved in the octamer.

Question 3

What are the main structures in which DNA packages?

Answer 3

1. Short region od DNA helix.
2. Beads on string form of chromatin.
3. 30nm chromatin fiber packed nucleosomes.
4. Section of chromosome in extended form.
5. Condensed section of chromosome.
6. Mitotic chromosome.

Question 4

What is heterochromatin?

Answer 4

Inactive form of DNA around the centromere and telomere. Facultative as it contains silent genes and regulated differently between cells.

Question 5

What is euchromatin ?

Answer 5

Active and light form of DNA.

Question 6

What are TADs?

Answer 6

Topologically associated domains. They restrict interactions of sequences and regulate genes/ keep region of chromatin functionally separated from each other.

Question 7

What are LADs?

Answer 7

Lamina associated domains. They are gene poor and heterochromatic, 2 types constitutive and facultative. They aid functional organization of genome.

Question 8

What are NADs?

Answer 8

Nucleus associated domains. They organise chromosomes and are associated with gene expression.

Question 9

What are the chromosome compartments?

Answer 9

A is the active compartment, B is inactive. More interactions between A’s and vice versa with B.

Question 10

What happens to the nucleosomes during replication?

Answer 10

Nucleosomes are removed ahead of replication fork, replaced after replication fork as a mixture of old and new histones.