Epigenetics/ Gene Expression

Question 1

Epigenetics def.

Answer 1

• Epigenetics is the heritable change in gene function, without changing DNA base sequence.
• Changes caused by changes in environment.

Question 2

What will be added to DNA if the idea of epigenetics is occurring? What factors could cause this?

Answer 2

• Environmental factors: diet, stress, toxins cause this.
• Add epigenetic tags to DNA, altering gene expression in eukaryotes.

Question 3

Epigenome def.

Answer 3

• Single layer of chemical tags on DNA.
• Impacts the shape of DNA-histone complex/ whether DNA is tightly wound –> so won’t be expressed OR less tightly wound –> so will be expressed.

Question 4

How can the epigenome inhibit transcription?

Answer 4

• If the DNA is tightly wound around histones, transcription factors cannot bind, transcription inhibited —–> gene not expressed.

Question 5

What is meant by “gene expression?”

Answer 5

• Process of protein synthesis (ie. transcription/ translation.)

Question 6

What is DNA methylation and the effect it has?

Answer 6

• Methyl groups are added to promoter region of DNA–> to the cytosine base.
• Promotor region of DNA changes shape.
• Prevents transcription factors from binding –.> inhibits transcription of section of DNA –> decrease gene expression.

Diagram in Ellor notes.

Question 7

What is DNA acetylation and what effect does it have?

Answer 7

• Acetyl groups added to histones.
  ( Acetyl groups added–> histones become less positively-charged –> less attracted to phosphate group in DNA)
• DNA less tightly wound around histones
• DNA = more accessible to transcription factors/ transcription factors can bind to promotor region of DNA, transcription increases –> increase in gene expression.

Diagram in Ellor notes
() - extra info for clarification

Question 8

What charge do histones/ DNA have?

Answer 8

• Histones: positively-charged.
• DNA: negatively-charged.

Question 9

What effect does removal of acetyl groups have on gene expression?

Answer 9

• Decrease in gene expression.

Question 10

True or False

Acetyl and methyl groups are added to the histones in the DNA histone- complex.

Answer 10

• False.
• Acetyl groups ARE added to proteins but methyl groups are added to promoter region of DNA.

Question 11

True or False

Histones are tightly wound around DNA.

Answer 11

• False!
• DNA is tightly wound around histones.

Question 12

What are tumour suppressor genes? What would a mutation in these genes lead to?

Answer 12

• Genes that produce proteins to slow down cell division and cause cell death if DNA copying errors.
• Mutation in tumour supressor gene: uncontrolled abnormal cell division (as abnormal cells not identified/ destroyed) –> tumour.

() - extra info for clarification.

Question 13

What causes a tumour supressor gene to be turned off?

Answer 13

• Increased methylation –> more methyl groups added to DNA –> becomes inactivated/ turned off.

Question 14

What are oncogenes? What effect does decreased methylation have?

Answer 14

• Mutated versions of normal gene (proto-oncogene) that stimulates uncontrolled cell division.
• Decreased methylation of proto-oncogene. Results in oncogene –> which is constantly turned on.

Question 15

Which specific region of DNA will gain methyl groups during DNA methylation?

Answer 15

• Promoter region of DNA.
• Specifically cytosine bases.