CGE: Epigenetic Control of Gene Expression

Question 1

What can epigenetic control determine?

Answer 1

Whether a gene is switched on or off/ whether or not it is expressed.

Question 2

How does epigenetic control work?

Answer 2

Through the attachment or removal of chemical groups (epigenetic markers) to or from DNA or histone proteins.

Question 3

What do epigenetic marks do?

Answer 3

Alter how easy it is for enzymes (and other proteins needed for transcription) to interact with and transribe DNA.

Question 4

What can epigenetic changes occur in response to?

Answer 4

Changes in the environment.

Question 5

Can epigenetic changes be inherited?

Answer 5

Yes.

• Most epigenetic markers are removed between generations, but some can escape the removal process.

Question 6

Give an example of where epigenetic changes have been passed onto offspring:

Answer 6

Epigenetic changes in some plants in response to drought have been passed on to later generations.

Question 7

Give two methods of epigenetic control:

Answer 7

Methylation.

Acetylation of histones.

Question 8

What does increased methylation do to a gene?

How?

Answer 8

Switches a gene off.

• Methyl group attaches to CpG site.
• This is where a cytosine and guanine base are next to each other and linked by a phosphodiester bond.
• Changes the DNA structure so transcriptional machinery can’t interact with the gene.
• Gene is not expressed.

Question 9

What does decreased acetylation of histones do to a gene?

How?

Answer 9

Prevents expression of a gene.

• Removal of acetyl groups from histones causes chromatin to become highly condensed.
• Makes genes in DNA less accessible to transcriptional factors.

Question 10

What happens when histones are acetylated?

Answer 10

• Chromatin is less condensed.
• DNA and genes are more accessible to transcriptional machinery.
• Gene is transcribed.

Question 11

What enzymes are responsible for the removal of acetyl groups?

Answer 11

Histone deacetylase.

Question 12

What can epigenetics lead to?

Answer 12

The development of diseases.

Question 13

Name and describe a disease that epigenetics plays a role in the development of:

Answer 13

Fragile-X syndrome

• Causes learning and behavioural difficulties, and characteristic physical features.

Question 14

What causes fragile-x syndrome?

Answer 14

• Duplication mutation in gene on x chromosome (FMR1).
• DNA sequence CGG is repeated more times.
• There are more CpG sites - results in increased methylation of the gene.
• Switches gene off - protein isn’t produced and symptoms develop.

Question 15

Why are epigenetic changes good targets for drug treatments?

Answer 15

They are reversible changes - so the diseases they cause are too.

Question 16

How can drugs be used to combat epigentic changes?

Answer 16

• Ones that stop DNA methylation can reverse diseases caused by increased methylation - eg. chemotherapy drugs that stop increased methylation of tumour supressor genes.
• HDAC inhibitor drugs stop HDAC enzymes from removing acetyl groups from histones, allowing the gene to be transcribed.

Question 17

What is a problem with developing drugs that counteract epigenetic changes?

Answer 17

Changes take place in a lot of cells, so the drugs need to be as specific as possible to avoid damaging normal body cells.