B: Chromatin + histones

Question 1

Structure of nucleosome

Answer 1

• DNA wrapped around complex of 8 histones
• 4 Core histones (H2A, H2B, H3 + H4) and a linker histone (H1)
• 4 core histones form histone octamer complex with 2 copies of each core histone
• H2A forms dimer with H2B
• H3 forms dimer with H4

Question 2

Nucleosome?

Answer 2

DNA + histone octamer

Question 3

H1 job?

Answer 3

Histone H1 binds to linker DNA and induces tighter DNA wrapped around nucleosome and compacts DNA further

Question 4

Chromatin?

Answer 4

Complex of nucleosomes, H2 transcription factors + other proteins

Question 5

Functions of chromatin

Answer 5

Compaction + organisation of DNA
Regulation of gene expression

Question 6

Topoisomerases?

Answer 6

Proteins that can coil DNA and relax coiled DNA.
Topoisomerase II is major protein in scaffold.

Question 7

Nucleosome bead contains:

Answer 7

2x histone 2A
2x histone 2B
2x H3
2x H4
DNA

Question 8

Histones contain

Answer 8

• N terminal tail that is unique to each histone
• Common histone fold region made of 3 alpha helical regions
• short C terminal tail

Question 9

Main N terminal modifications that occur

Answer 9

• Lysines can be acetylated, methylated, sumolated (addition of string of specific amino acids), ubiquinated (addition of a different string of amino acid) and ribosylated (addition of ribose sugar)
• Arginines can be methylated
• Serines and threonines can be phosphorylated