Epigenetics and Gene Expression

Question 1

What do epigenetics do to genes?

Answer 1

Change their function without changing the sequence of DNA.

Question 2

What does the epigenome determine?

Answer 2

Determines the shape of the DNA - histone complex.

Question 3

Addition of what functional group to histones can chemically modify it?

Answer 3

Acetyl

Question 4

Addition of what functional group to DNA can chemically modify it?

Answer 4

Methyl

Question 5

Increased methylation and decreased acetylation of DNA is caused by what?

Answer 5

Changes to lifestyle and diet.

Question 6

What do methyl groups do to histones?

Answer 6

Increase how tightly wrapped around the DNA is to the histones.

Question 7

How can hypermethylation affect gene expression?

Answer 7

Decreases it

Question 8

Describe how hypermethylation can inhibit transcription.

Answer 8

1. Methyl groups are added to nucleotides
2. This blocks the site, inhibiting the binding of the activated transcription factor
3. This means that DNA helicase and the transcription factor are unable to break hydrogen bonds between bases and RNA cannot be produced.

Question 9

What charge do histones have?

Answer 9

Positive

Question 10

What charge does DNA have?

Answer 10

Negative

Question 11

How is the DNA-histone complex held together?

Answer 11

The positively charged histone attracts to the negative charge of the DNA, holding both together.

Question 12

Give the formula of an acetyl functional group.

Answer 12

CH3OR

Question 13

How does removing of acetyl groups change the charge of the histone proteins?
Therefore, how does this affect the attraction

Answer 13

Removing of acetyl groups increases the positive charge of the histone proteins.
This therefore increases the attraction between the DNA and histone as they become more tightly wrapped.

Question 14

How does increased acetylation of histones change attraction between DNA?

Answer 14

Increased acetylation decreases attraction between the 2 because it removed a bond between the histone and DNA. Therefore, the DNA is less tightly wound around the histone.

Question 15

If DNA is less tightly wrapped, how does this effect gene expression?

Answer 15

If DNA is less tightly wrapped, then RNA polymerase and transcription factors can more easily bind.

Question 16

Describe how alterations to tumour suppressor genes can lead to development of tumours.

Answer 16

Increased methylation can mean that genes are not transcribed as the DNA histone complex is too tight.
This means tumour suppressor genes are not expressed so rate of cell division is not controlled.

Question 17

Describe how a substitution mutation can lead to formation of an enzyme that no longer functions.

Answer 17

Substitutions can change amino acid produced.
This can lead to a different tertiary protein structure as hydrogen bonds, disulfide bridges etc form in different places.
This means the enzyme is no longer complimentary to the substrate and enzyme substrate complexes can no longer form.

Question 18

One mutation causing PKU was originally only found in one population in Asia. Later on, it was found in many. State why.

Answer 18

The founder effect. People from the original population migrate elsewhere, taking the mutated gene elsewhere.

Question 19

Define what is meant by epigenetics.

Answer 19

Heritable changes in gene function without changing the base sequence of DNA.

Question 20

Explain how increased methylation could lead to cancer.

Answer 20

Methyl groups could be added to tumour suppressor genes.
This means the transcription of tumour suppressor genes is inhibited.
This leads to uncontrollable cell division.