Question

The role of most microRNAs within a eukaryotic cell is to:

Question 5

	1) associate with ribosomal proteins to facilitate translation.
	2) repress the expression of genes by inhibiting translation of specific mRNAs.
	3) regulate RNA polymerase activity in the nucleus.
	4) regulate the splicing of primary transcripts to mRNAs.
	5) bind with other RNAs to stabilize their secondary structure.

Describe two epigenetic modifications known to facilitate the expression of genes in eukaryotes.

Answer 1

5) microRNA associate with the RISC complex.

microRNA can block the translation if the microRNA is partially complementary to mRNA or Degrade the mRNA if the microRNA is completely complementary to mRNA.

so the answer is 1) repress the expression of genes by inhibiting the translation of specific mRNAs.

6) Histone acetylation: Histone acetyltransferase acetylates N terminal histone residues of the histones, acetylation decreases the negative charge on the histone, so the interaction between DNA and histones( negatively charged DNA and positively charged histones interact via electrostatic interactions) decreases so DNA becomes loosely packed so chromatin becomes euchromatin and the level of expression increases.

H3K4 me3 - trimethylation of histone 3 on the lysine residue at 4 th position is an example of active mark, it increases the rate of transcription, H3K4me3 is produced by a histone methyl transferase.