Lecture 5

Question 1

What is a classic epigenetic mark?

Answer 1

DNA-methylation : 5-methylcytosine

Question 2

What is special about 5-methylcytosine

Answer 2

Can be propagated across divisions
associated with gene transcription

Question 3

What are CpG islands?

Answer 3

CG dinucleotides enriched at many promoters

Question 4

How is the nucleosome organized?

Answer 4

four histones with 2 copies each (octamere)

Question 5

What are the core histones?

Answer 5

H2A, H2B, H3, H4: H1 is a linker histone (one per nucleosome)

Question 6

Where does histone - DNA contact take place?

Answer 6

Histone fold domain

Question 7

hat is special about the histone fold domain?

Answer 7

Unstructered N-terminal (site of post translational modification)

Question 8

What do H2A, H2b histones form and what does H3 and H4 histones form?

Answer 8

(H2A, H2B) dimers and (H3, H4) tetrameres respectively

Question 9

What does chormatine folding do?

Answer 9

GHene silencing

Question 10

What is the difference between constitutive heterochromatine and facultative heterochromatine

Answer 10

constitutive heterochromatine:
independent of cell type
little transcription
repetetive sequences (structure regions)

facultative heterochromatine:
inactive gene regions
cell type specific
coding regions

Question 11

What are functions of nucleosomes

Answer 11

packaging
signaling
transcription obstacle

Question 12

What are the two classes of epigenetic regulators

Answer 12

chromatine remodelers
chromatine modifiers

Question 13

What is the role of chromatine modifications

Answer 13

development (gene expression patterns) and transcription
signature modifications are essential for genetic processes

Question 14

where are histones normally modified?

Answer 14

N-terminally (histone code are all modifications)

Question 15

What does lysine acetylationd do?

Answer 15

lysine has positive charge, which is removed by acetylation -> eviction of nucleosome and enables transcription

Question 16

Are epigenetic marks reversible?

Answer 16

Yes

Question 17

What are READER domains and how do they work?

Answer 17

Site of Post translational modification allow for recruitment and regulation

Question 18

When are histones normally synthesized?

Answer 18

During the S-phase

Question 18

What are histone chaperones and what do they do?

Answer 18

Prevent histone-DNA aggregation -> bind histones and are specific for histone variants

Question 19

What does the variant H2A.Z do?

Answer 19

Marks boundaries of nucleosome-free and nucleosome-containing regions

Question 20

Do histone chaperones use ATP?

Answer 20

No

Question 21

Do histone remodelers use ATP?

Answer 21

Yes

Question 22

What do histone remodelers do?

Answer 22

Can establish spacing between nucleosomes, can grant DNA access, can edit Nucleosomes

Question 23

What happens during transcription elongation?

Answer 23

Nucleosomes dissasembled and reassembled: Histone chaperone FACT removes H2A/H2B for RNA Poly II to pass

Question 24

What are Oncohistones?

Answer 24

Histone modifications that affect Post translational modification level. Very specific for different tumors