Small RNAs

Question 1

What are non-coding RNAs?

Answer 1

Any RNA not translated into a protein

Such as

• microRNA - control translation
• siRNA - viral defence
• piRNA - germ cell prodn
• long ncRNA - inactivates X chromosome

Includes tRNA and rRNA

Question 2

What is the function of regulatory RNA?

Answer 2

To control which mRNA gets translated.

Evidence is Lin 4 w Lin 14 - inverse relationship - Lin 4 silences mRNA that forms Lin 14

Question 3

Carrying on, what is RNA interference?

Answer 3

Where an mRNA is silenced - by being masked by a double stranded RNA

microRNA is endogenous
siRNA is exogenous

Question 4

How is an RNAi substrate generated? (siRNA)

Answer 4

siRA enters cytoplasm

DICER breaks it into duplex fragments, with overhangs

Ago attaches to overhangs, forming RISC which binds to complimentary mRNA and cleaves it

Question 5

What is a microRNA

Answer 5

Hairpin RNA synthesised in nucleus by RNA Pol 2, with a 2 nucleotide overhang on 3’ end

Question 6

How does it inhibit target mRNA?

Answer 6

Cleavage

Incorrect base pairing

• Creates bulge, so less stringent mathching
• Forms RISC, which allows it to join mRNA
• This is permanently bound now and hence mRNA is useless