The Control of Gene Expression: Gene Expression is Controlled by a Number of Features - Regulation of Transcription and Translation, Epigenetics

Question 1

What does epigenetics control in eukaryotes?

Answer 1

• In eurkaryotes, epigenetic controls gene expression

Question 2

How does epigenetic control work?

Answer 2

• Involves heritable changes in gene function, without changes to base sequence of DNA
• Chemical groups called epigenetic marks are either attached or removed from DNA or histone proteins

Question 3

What causes epigenetic control?

Answer 3

• Epigenetic changes are caused by changes in the environment that inhibit transcription by:
• Increased methylation of DNA
• Decreased acylation of associated histones

Question 4

Which epigenetic mechanisms used to control gene expression do you need to know about?

Answer 4

• Increased methylation of DNA

- Acetylation of histones

Question 5

Increased methylation of DNA

Answer 5

• An epigenetic mark, a methyl group (-CH3), is attached to the DNA coding for a gene
• Methyl group always attaches to a CpG site
• DNA methyl transferase attaches methyl group to cytosine
• Increased methylation changes the DNA structure (makes DNA very condensed and histones very close) so transcriptional machinery can’t interact with gene
• Gene is not expressed

Question 6

What is a CpG site?

Answer 6

• Where a cytosine and guanine base, linked by a phosphodiester bond, are next to each other in DNA

Question 7

Which enzyme attaches methyl groups to cytosine?

Answer 7

• DNA methyl transferase

Question 8

Does increased methylation lead to genes being expressed or not?

Answer 8

• Leads to genes not being expressed

Question 9

How does the interaction between histones and chromatin affect transcription?

Answer 9

• Histones are proteins that DNA wraps around to form chromatin, which makes up chromosomes
• Chromatins can be highly or less condensed
• If chromatins are too condensed, transcriptional machinery cannot access DNA so transcription doesn’t occur

Question 10

Decreased acylation of histones

Answer 10

• An acetyl group, another epigenetic mark, can be added or removed from histones

• Increased acetylation

• When histones are acetylated, the chromatin is less condensed
• Transcriptional machinery can access DNA, allowing genes to be transcribed

• Decreased acetylation

• When acetyl groups are removed from histones, chromatin becomes highly condensed
• Transcriptional machinery can’t access gene
• Histone deacytlase (HDAC) enzymes remove acetyl groups

Question 11

Which enzyme is responsible for removing acetyl groups from histones?

Answer 11

• Histone deactylase (HDAC)

Question 12

Does increased and decreased acetylation lead to genes being expressed or not?

Answer 12

• Increased acetylation
- Leads to genes being expressed

• Decreased acetylation
- Leads to genes not being expressed

Question 13

Compare the effects of increased methylation and decreased acylation

Answer 13