Small RNAs in the regulation of biological processes

Question 1

What are micro RNAs (miRNA)

Answer 1

control the translation of perhaps most genes

Question 2

What is a heterochromatin

Answer 2

chromosome material of different density from normal (usually greater), in which the activity of the genes is modified or suppressed. X-inactivation prevents female cells from having twice as many X chromosome genes as males cells, which only possess a single copy of the X chromosome

Question 3

List the steps for RNA Interference

Answer 3

The long dsRNA is cleaved by an endo-ribonuclease called Dicer. Dicer cuts the long dsRNA to form short interfering RNA or siRNA; this is what enables the molecules to form the RNA-Induced Silencing Complex (RISC). Once the siRNA is part of the RISC complex, the siRNA is unwound to form single stranded siRNA. Requires “Argonaute-Piwi” proteins The single stranded siRNA which is part of the RISC complex now can scan and find a complementary mRNA Once the single stranded siRNA (part of the RISC complex) binds to its target mRNA, it induces mRNA cleavage. The mRNA is now cut and recognized as abnormal by the cell. This causes degradation of the mRNA and in turn no translation of the mRNA into amino acids and then proteins. Thus silencing the gene that encodes that mRNA. add pic

Question 4

Is dsRNA found in animals or plants

Answer 4

plants

Question 5

Explain the process which turns pri-mRNA into pre-mRNA

Answer 5

1) Transcribed by RNA polymerase II or III into a long primary pri-miRNA transcript with a stem-loop structure of up to several kilobases in length. 2) pri-miRNA is processed by Drosha into a shorter pre-mRNA. 3)The pre-miRNA is small enough to be transported from the nucleus to the cytoplasm. add pic

Question 6

What does shRNA mean

Answer 6

short hairpin RNA

Question 7

What converts pre-miRNA into si-RNA

Answer 7

Dicer add pic

Question 8

Where do most miRNA target sites lie?

Answer 8

3’ UTR

Question 9

How do miRNAs inhibit target mRNAs?

Answer 9

miRNAs inhibit target mRNAs through base pairing with incomplete complementarity

Question 10

Plant miRNAs usually have near-perfect pairing with their mRNA targets, which induces gene repression through cleavage of the target transcripts. In contrast, animal miRNAs are able to recognize their target mRNAs by using as little as 6–8 nucleotides (the seed region) at the 5’ end of the miRNA,[10][20][21] which is not enough pairing to induce cleavage of the target mRNAs.[4]

Answer 10

add pic