Chromatin and Gene Expression

Question 1

— are the largest protein component of — and organize DNA into “beads
on a string”

Answer 1

Histones

chromatin

Question 2

How was chromatin discovered?

Answer 2

• nuclei were isolated from cells and treated with MNase (nuclease that cleaves any DNA not bound to proteins)
• on gel, showed laddering pattern
• each ladder of DNA is abouve ~150bp apart
• indicated a repeat unit

Question 3

The basic unit of chromatin structure is called a – that is composed of
– histone proteins plus – of DNA

Answer 3

nucleosome

8

147bp

Question 4

what is the core histone octamer made of?

Answer 4

2 copies of each core histone: H2A, H2B, H3, and H4, tail of each histone protein is exposed

DNA makes 1.7 turns around this octamer

Question 5

What is histone H1? what does it help with?

Answer 5

histone linker protein that sits on top of nucleosome core and interacts with DNA between adjacent nucleosomes

compacts nucleosomes into chromatosome structure

Question 6

What are the 2 steps for gene activation for the transcription to be accessible?

Answer 6

• nucleosome/chromaitin altered to relieve repressed transcriptional state
• interaction of RNAPII and GTFs with the promoter

Question 7

How does the transcription machinery access DNA?

Answer 7

1. chromatin-remodelling complexes: mediate ATP-dependent conformational changes in nucleosome structure
2. Histone-modifying enzymes: introduce covalent modifications into the N-terminal tails of the histone proteins

Question 8

A code based on — determines gene expression through selective recruitment of proteins

Answer 8

histone-tail covalent
modifications

tails are unqiue to which enzymes can recognize them

Question 9

Prominent forms of histone covalent modification are

Answer 9

• lysine acetylation (relax)
• lysine methylation (relax or condense)
• serine phosphorylation (relax)
• lysine ubiquitination
• lysine sumoylation

Question 10

What is the histone code hypothesis?

Answer 10

specific chemical modification pattern on histone protein affects gene expression by controlling DNA accessibility to transcriptional machinery.

Question 11

What are the key activities required for the histone code hypothesis?

Answer 11

• writers (add meth, phos)
• erasers (remove)
• readers bind and interpret modification (TF, regulars)

Question 12

What is the locus control gene?

Answer 12

segment of gene that enhances transcription of a clster of linked genes by inducing a more open conformation of the chromatin flanking the locus