20.4 Epigenetic control of gene expression

Question 1

What is epigenetics

Answer 1

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

Question 2

What is the epigenome

Answer 2

The lifetime accumulation of chemical tags on DNA and histones.

Question 3

What does acetylation affect

Answer 3

HISTONES

Question 4

What does methylation affect

Answer 4

DNA

Question 5

How does acetylation have an effect

Answer 5

An acetyl group is transferred to a molecule. Decreased acetylation (Removal) increases the positive charges on histones and increases their attraction to the phosphate groups on DNA, making DNA inaccessible to TFs

Question 6

How does methylation have an effect

Answer 6

1. Physically prevents the binding of TFs to the DNA
2. Attracts proteins that condense the DNA-histone complex (by inducing the deacetylation of the histones) making the DNA inaccessible to TFs

Question 7

What is a DNA-histone complex

Answer 7

The combination of DNA and proteins called histones.

When the association of histones with DNA is weak, the DNA-histone complex is less condensed. This means the DNA is accessible by TFs, which can initiate the production of mRNA

When the association of histones with DNA is strong, the DNA-histone complex is more condensed. THis measn the DNA isnt accessible by TFs, therefore the gene isnt expressed

Question 8

What can occur in eukaryotes and some prokaryotes in regards to RNA interference

Answer 8

The translation of mRNA produced by a gene can be inhibited by breaking mRNA down before its coded information can be translated into a polypeptide.

One type of RNA molecule involved is Small Interfering RNA

Question 9

What is the mechanism of Small Interfering RNA (siRNA)

Answer 9

1. An enzyme cuts large double-stranded molecules of RNA into smaller sections called small interfering RNA
2. One of the two siRNA strands combines with an enzyme
3. The siRNA molecule guides the enzyme to a mRNA molecule by pairing up its bases with the complementary ones on a section of the mRNA
4. The mRNA is no longer capable of being translated into a polypeptide
5. This means that the gene has not been expressed, it has in fact been blocked.