L24

Question 1

let-7

Answer 1

encodes a conserved 21 nucleotide RNA

Question 2

lin-4

Answer 2

inhibits 3’UTR of lin-14

Question 3

miRNA

Answer 3

• 20-25 nucleotides long
• regulates many genes
• ex) lin-4, let-7

Question 4

RNAi mechanism

Answer 4

1) Dicer cleave dsRNA into siRNA
2) RISC separate siRNA strands
3) siRNA bind to complementary mRNA
4) RISC cleaves mRNA to block translation

Question 5

RNAi: dicer cleaves

Answer 5

dsRNA into siRNA

Question 6

RNAi: who separates what

Answer 6

RISC binds to the siRNA and separates its strands

Question 6

RNAi: siRNA binds to what

Answer 6

siRNA binds to complementary mRNA

Question 7

siRNA

Answer 7

short interfering RNA

Question 8

RISC

Answer 8

RNA-induced silencing complex, includes slicer

Question 9

miRNA are generated from

Answer 9

stem-loop precursors

Question 10

RNAi vs miRNA

Answer 10

cleaves the message by perfect base pairing vs imperfect base pairing that doesn’t cleave but repress target

Question 11

dsRNA normally comes from

Answer 11

viruses, so dsRNA natural function to silence them

Question 12

dicer

Answer 12

endonuclease that cleaves RNA duplexes

Question 13

dicer substrate

Answer 13

dsRNA duplex or ss hairpin

Question 14

sources of siRNA and miRNA molecules

Answer 14

RNA dependent RNA polymerase (RdRP)

Question 15

How does RISC complex block translation?

Answer 15

bind to 3’ region of mRNA

Question 16

Micro-RNAs (miRNAs) inhibit the expression of specific genes mainly by
blocking translation of mRNA
activating DNases to destroy those genes
base pairing with the genes to prevent their transcription
targeting their mRNAs for degradation

Answer 16

blocking translation of mRNA

Question 17

Which statement best describes the main distinction between the origin of the two classes of small regulatory RNAs: siRNA and miRNA?
- siRNAs originate within the cell cytoplasm; miRNAs originate from the cell genome
- siRNAs originate from predominantly exogenous dsRNA; miRNAs originate from the cell genome
- miRNAs are expressed whenever siRNAs are unable to appropriately degrade RNA sequences
- miRNAs are processed from dsRNA viruses, siRNAs are processed from ssRNA viruses

Answer 17

siRNAs originate from predominantly exogenous dsRNA; miRNAs originate from the cell genome

Question 18

Which statement best describes the distinction between the purposes of the two RNAi pathways within the eukaryotic cell?
- siRNA-mediated gene silencing represents a cell defence mechanism against exogenous dsRNA; miRNA-mediated gene silencing is an integral gene expression regulation process
- miRNA and siRNA-mediated gene silencing represent evolutionary-independent pathways which confer identical silencing mechanisms on the target dsRNA
- miRNA-mediated gene silencing represents a back-up pathway should siRNA-mediated gene silencing be unsuccessful at silencing the target dsRNA
- siRNA and miRNA-mediated gene silencing pathways must both be active to successfully silence the target dsRNA

Answer 18

• siRNA-mediated gene silencing represents a cell defence mechanism against exogenous dsRNA; miRNA-mediated gene silencing is an integral gene expression regulation process

Question 19

The enzyme dicer is responsible for
cutting double-stranded RNAs into short pieces
repair of mistakes made in DNA replication
unwinding double-stranded RNAs
transposition of certain transposons

Answer 19

cutting double-stranded RNAs into short pieces

Question 20

All of the following are involved in translating information into proteins EXCEPT:
snRNA
siRNA
tRNA
rRNA

Answer 20

siRNA

Question 21

In RNAi, genes are silenced using:
dsDNA
dsRNA
ssRNA
ssDNA

Answer 21

dsRNA

Question 22

Which organism uses CRISPR as a defense system?
phage
bacteria
humans
Tetrahymena
yeast

Answer 22

bacteria

Question 23

RNAi: RISC cleaves

Answer 23

the mRNA so that it cannot be translated

Question 24

You perform an experiment where you add antisense RNA to your favorite gene. You see that you inhibit the function of this gene. Why? Response recorded A. Because adding antisense RNA confuses RNAP and inhibits transcription B. Because antisense RNA can pair with sense RNA and block its translation C. Because antisense RNA binds to the 3’UTR of the gene and inhibits translation. D. Because you form dsRNA, which leads to degradation of the mRNA.

Answer 24

D. Because you form dsRNA, which leads to degradation of the mRNA.

Question 25

Levels of which of the following are NOT usually decreased by dsRNA? Response recorded A. Pre-mRNA B. Processed mRNA C. Protein D. All are decreased E. None are decreased

Answer 25

kind of A and kind of D because pre-mRNA is partially decreased

Question 26

Levels of which of the following are NOT usually decreased by miRNA? Response recorded A. Pre-mRNA B. mRNA C. Protein D. All are decreased E. None are decreased

Answer 26

A. Pre-mRNA