1.4 - Epigenetics

Question 1

What is epigenetics?

Answer 1

the study of heritable changes in gene expression and gene function that cannot be explained by changes in DNA sequence

Question 2

What is the epigenome?

Answer 2

all of the epigenetic marks on the genome

Question 3

What can epigenetic arks be influenced by?

Answer 3

• diet
• chemical exposure
• medication

Question 4

Explain DNA methylation

Answer 4

• prokaryotes and eukaryotes
• methyl group is transferred to the cytosine nucleotide
• carried out by writer enzymes and reversed by eraser enzymes

Question 5

What is the role of a writer enzyme?

Answer 5

• transfer a methyl group to a cytosine

Question 6

What is the role of an eraser enzyme?

Answer 6

• remove a methyl group from a cytosine

Question 7

What is the effect of methylation in the promoter region?

Answer 7

• inhibits binding of TFs

Question 8

What is the role of reader proteins?

Answer 8

• recognise methylated DNA
• they have an affinity for methylated cytosines
• they can then promote or inhibit the recruitment of other proteins (such as those involved in transcription)

Question 9

How are epigenetic marks maintained in DNA replication?

Answer 9

• because DNA replication is semi conservative
• methylated cytosines will then only be on one strand
• reader proteins can then recruit writer proteins to methylate the other strand

Question 10

What are epigenetic marks on histones?

Answer 10

• post-translational modifications
• impacts gene expression
• marks can be recognised by readers and removed by erasers

Question 11

Name the 4 different histones found in nucleosomes

Answer 11

• H2A
• H2B
• H3
• H4

Question 12

What can writers do to histones?

Answer 12

• acetylate
• methylate
• phosphorylate
• ubiquitinate

Question 13

Explain H3K9ac

Answer 13

Histone 3, lysine (K) residue at position 9, acetylated

• DNA - , histones +
• acetylation by writers neutralises positive charge while recruiting readers
• looser packaged DNA
• more accessible to transcription machinery

Question 14

Explain H3K27me3

Answer 14

Histone 3, lysine (K) residue at point 27, tri (3) - methylated

• readers affect relative nucleosome positioning and packaging
• in this case leads to highly packed nucleosomes (condensed)
• transcription machinery cannot get in
• genes silenced

Question 15

What is the effect of which histone being methylated?

Answer 15

it can lead to either repression or activation of transcription

Question 16

How are histone marks maintained during replication?

Answer 16

• nucleosomes disassembled before replication fork and reassembled afterwards
• parental histones partition equally between daughter strands, and new histones are added
• marks on parental histones recruit reader proteins to add marks to cytosolic histones

Question 17

How many generations in plants and animals are required to prove transgenerational inheritance?

Answer 17

• animals - 3 (as it has to affect the germ line which is set aside early in development)
• plants - 2

Question 18

What needs to happen for transgenerational epigenetic inheritance?

Answer 18

• marks must be present in the germ line
• need to be passed on even if there is no environmental trigger
• marks tend to be removed by eraser proteins in animal gametes - not removed in plants
• will be inherited if erasure is incomplete or marks are re-established
• happens in plants have not proven if in animals

Question 19

How does epigenetics affect translation?

Answer 19

non-coding RNA

Question 20

What are modulators of DNA methylation?

Answer 20

• phenolics