Lecture 8- small RNAs

Question 1

2 main types of small RNA

Answer 1

siRNA (small interfering)
miRNA (micro)

Question 2

importance of miRNAs (statistics)

Answer 2

control 60% of the genome, make up about 1-3% total

Question 3

structure

Answer 3

hairpins made up of 18-25 nts, eventually form a complex (RISC)

Question 4

some differences between plant and animal miRNAs

Answer 4

more likely to form clusters in animals, can be synthesised in the cytoplasm in animals (in the nucleus in both), binding motif is at the 3’ UTR in animals and 5’UTR or ORF for plants

Question 5

differences in synthesis in plants and animals

Answer 5

diver/DCL1 action happens in the cytoplasm of animals, in the nucleus of plants
diffferent end group on the mature miRNA, -OH in animals, -OCH3 in plants

Question 6

what are siRNAs derived from

Answer 6

dsRNA, from viruses, heterochromatin, transposons etc

Question 7

siRNA function

Answer 7

cleavage of mRNAs, rather than translational depression

Question 8

siRNA production

Answer 8

dsRNA formation, transport into the cytoplasm, diver cutting up dsRNA, ssRNA forms an association with Ago and rest of the RISC, leading to cleavage

Question 9

self amplification of siRNAs

Answer 9

siRNAs act as primers for RDR when their cap is lost (can happen during infections etc), which leads to their transformation into dsRNA and processing back into siRNAs

Question 10

involvement of siRNAs in DNA methylation

Answer 10

siRNA signals can direct methylation enzymes, or break down proteins needed for demethylation such as DNA glycosylases

Question 12

RNAi-mediated histone methylation

Answer 12

siRNAs can also bind histone methylating proteins to the histone, then more proteins can bind to help stabilise the methylation

Question 13

examples of uses of sRNAs

Answer 13

therapeutics, used to help ‘mop up’ deleterious sRNAs so they can’t silence proteins
agriculture to aid in plant resistance, interfering with ckRNAi