epigenetics

Question 1

nucleus structure

what do the nucleoli contain?

Answer 1

contains:

• rDNA
• rDNA synthesis
• ribosome assembly

Question 2

chromatin

what are the 2 two types of chromatin?

Answer 2

heterochromatin:
- tightly packed DNA, not transciptionally active

euchromatin:
- less tightly packed, site of active transcription

Question 3

epigenetic control of gene expression

define epigenetics

Answer 3

• regulartion of gene expression by modifications to the DNA and chromatin structure which do not alter the underlying DNA sequence

Question 4

DNA methylation

outline what happens to gene transcription when methylation is:
- High
- low

Answer 4

high methylation: less tightly packed chromatins, so transcription factors have more access to sections of DNA so more transcription can occur

low methylation: more tightly packed chromatins, so transcription factors have less access to sections of DNA meaning less transcription occurs

Question 5

dna methylation

where does cytosine methylation often occur

Answer 5

often occurs at clusters of cytosine-guanine dinucleotides (CpG)

Question 6

developmental remodelling of DNA methylation

why does the parental methylation patterns in the gametes need to be removed from the developing embryo?

Answer 6

so that the embryonic methylation pattern can be established

Question 7

non-coding RNAs - micro RNAs

outline X chromosome inactivation

Answer 7

1. both X chromosomes in mother have the Xist gene but only one randomly expresses it.
2. this Xist is a non-coding RNA, and when expressed it binds on the chromosome all over, recruiting a series of modifications to the DNA.
3. this makes the X chromosome expressing this gene highly DNA methylated, shutting down this X chromosome

Question 8

histone acetylation

what happens to transcription when you have high and low Histone tail acetylation

Answer 8

high histone tail acetylation:
- more open chromatin structure so more transcription

low histone acetylation:
- less open chromatin structure so less transcription