Gene Expression and Epigenetics

Question 1

How does histone modification affect gene regulation?

Answer 1

When methylated, histones are positively charged, chromatin is condensed, no promoter access- transcription is repressed. When acetylated, histones become neutral, chromatin opens, allowing promoter access and transcription.

Question 2

What enzyme catalyses the acetylation of histones?

Answer 2

Histone acetyltransferase (HAT).

Question 3

What enzyme catalyses the methylation of histones?

Answer 3

Histone Deacetylase (HDAC).

Question 4

How does DNA methylation of CpG islands regulate gene expression?

Answer 4

Cis regulatory elements cannot bind the trans regulatory proteins when CpG islands are methylated.

Question 5

What happens when a CpG island has been methylated?

Answer 5

Transcription factor cannot bind. Methyl-CpG binding protein can bind. Recruits HDAC, which methylates histones and causes chromatin condensation.