08

Question 1

Chromosome puff

Answer 1

DNA loosens up, it’s being transcribed, compacts back when not needed

Lots of RNA molecules in the puff, less around it

Question 2

Nucleosome Positions

Answer 2

Nucleosome position is dynamic for transcriptional regulation

The positions of nucleosomes on the chromosome often change according to/in 2 ways:
1. Changes in the cell cycle
2. Transcriptional activity

Nucleosome-DNA interactions are dynamic

The forms of chromatin change during the cell cycle, becoming most condensed at mitosis

Question 3

Heterochromatin

Answer 3

Regions of DNA associated with many nucleosomes have lower rates of transcription

30nm fiber

Question 4

Euchromatin

Answer 4

It is important that some regions of the DNA have sparsely placed nucleosomes so that DNA regulatory proteins can bind to the DNA

Higher level of transcription

Beads on a string

Question 5

Histone Acetyltransferases (HATs)

Answer 5

puts acetyl group on

Question 6

Histone Deacetylase complexes (HDACs)

Answer 6

removes acetyl groups

Question 7

Histone Methyltransferases

Answer 7

puts methyl group on

Question 8

Histone Demethylases

Answer 8

removes methyl groups

Question 9

How are modifications of histones passed on during DNA replication?

Answer 9

Epigenetic inheritance, ensuring that daughter cells retain the same chromatin state as the parent cell

Question 10

Nucleosomes Assembly

Answer 10

Nucleosomes are assembled in an ordered fashion!
Step 1: Two H3-H4 dimers form a tetramer (bind 1st)
Step 2: H32:H42 tetramer binds to dsDNA
Step 3: Two H2A- H2B dimers bind are recruited to the DNA molecule forming a complete nucleosome
H3 + H4 contain many more marks than 2A + 2B [see photo earlier in doc with histone domains]

Question 11

How are histone tails modified?

Answer 11

P = Phosphorylation
Me = Methylation
Ac = Acetylation
Ub = Ubiquitination

Most modifications are on the N terminus

Question 12

Barrier Proteins

Answer 12

Stop the spread of heterochromatin

Heterochromatin can spread up to barrier, but not past it
Ensures that genes in euchromatin remain active and that heterochromatin boundaries are maintained for proper gene regulation

Lose barrier → chromosome translocation
Barrier protein moved, heterochromatin spreads

Different kinds of barrier proteins, hides next nucleosome