20. Chromosomes

Question 1

What is the packaging in DNA throughout the cell cycle?

Answer 1

DNA is in chromosomes only when the cell is dividing, at other times less organised - chromatin

Question 2

What is the composition of nucleosomes?

Answer 2

DNA wraped around histone proteins to form nucleosomes - separate nucleosomes are connected by linker DNA (no coding) → nuclease digests

To release DNA strand from histones → high concentration of salt used: DNA strand from 146 nucleotide pairs + 4 different histone proteins in a octomere

Question 3

What are the possible post-translational modifications in histone proteins?

Answer 3

Acetylation, phosphorylation, methylation, monoubiquitation - reversible - determine how the DNA is accessed

Question 4

How is DNA packaged further? What component is responsible for this?

Answer 4

10 nm fibre is further packaged into 30 nm fibre (coiled around more) → done by H1 histone protein

Question 5

What is the further fibre which is packaged from the 30 nm fibre?

Answer 5

30 nm fibre is packaged into 100 nm chromonema fibre

Question 6

Overview of chromatin compaction

Answer 6

That is how 3 metres of DNA can be fit in nucleus of 10 micrometers