Lecture 15: Epigenetics

Question 1

What are the two forms of info in the genome of cells?

Answer 1

Genetic info and epigenetic info

Question 2

What is epigenetic info?

Answer 2

additional info that can be modified for the regulation of gene expression.

Question 3

Define epigenetics?

Answer 3

On or over the genetic info encoded in the DNA. Is the study of reversible heritable changes in gene function that occur without a change in the sequence of nuclear DNA.

Question 4

What eventually happens to epigenetic markers?

Answer 4

They are lost or modified more easily.

Question 5

What is tight packing?

Answer 5

8 different proteins form a histone octamer with DNA wrapped around it to form a nucleosome. DNA is tightly packed around nucleosomes which are made of histones. the nucleosomes form more complex structures called chromatin fibres.

Question 6

What does how tightly DNA is wrapped around mean?

Answer 6

Determines how well RNA polymerase can be recruited and change gene expression patterns.

Question 7

What can alter higher order nucleosome structure?

Answer 7

Post-translational modification of histone tails be methylation, acetylation or phosphorylation

Question 8

What else can nucleosome structure be regulated by?

Answer 8

ATP-dependent chromatic remodellers.

Question 9

What are the epigenetic markers?

Answer 9

DNA methylation and histone modification

Question 10

What do methyltransferase do?

Answer 10

Transfer methyl groups to cytosines of CpG dinucleotides on both strands.

Question 11

What represses expression?

Answer 11

Methylated CpG islands close to promoter regions of genes

Question 12

What happens to methyl groups during DNA replication?

Answer 12

They are transferred to the new strands

Question 13

How many histones can be modified by how many processes and what processes?

Answer 13

4, 3, Ac, Me, P.

Question 14

What does histone acetylation do?

Answer 14

Loosens chromatin packaging and correlates with transcriptional activation

Question 15

What adds and removes the acetyl groups?

Answer 15

acetyl-co-A and histone deacetylases

Question 16

What is the effect of removing the acetyl groups?

Answer 16

re-establishes the positive charge in the histones which are associated with repression of transcription.

Question 17

What carries out histones methylation?

Answer 17

histone methyl transferase

Question 18

Where is histone methylation usually concentrated and what is it associated with

Answer 18

N terminus and silencing of gene expression.

Question 19

What is gene activation and silencing correlated with?

Answer 19

H3 and K9 acetylation and H3 and K9 methylation.

Question 20

What can different modifications at the same site do?

Answer 20

Have different effects on gene expression

Question 21

What else can histone methylation do?

Answer 21

can increase or decrease gene expression of nearby genes.

Question 22

What is histone phosphorylation associated with?

Answer 22

increased expression of proliferation associated genes but also with gene expression silencing.

Question 23

What increases during cell stress and DNA damage?

Answer 23

Histone phosphorylation

Question 24

What is associated with aggressiveness of cancer?

Answer 24

phosphorylation of histones near oncogenes

Question 25

Explain which of the modifications are retained or lost during cell division

Answer 25

Histone acetylation patterns are replication, histone methylated ones are lost

Question 26

What proteins promote and repress expression?

Answer 26

TrxG and PcG

Question 27

Explain why epigenetic change is important

Answer 27

Development of multicellular organisms is possible because epigenetic markers help maintain different cell states. Epigenetics mediates the silencing of alleles during imprinting. Some changes are passed on that allow us to adapt to environmental change. Changes in epigenetic control can lead to cancer.

Question 28

explain how epigenetic changes are important for maintaining cell differentiation

Answer 28

pluripotency genes eg OCT4 are methylated at H3K4 and expressed. late differentiation genes are marked by H3K27 in a manner dependent on the particular committed cell type.