lecture 8

Question 1

RNA editing

Answer 1

nucleotide alterations which result in different or additional nucleotides in the mature RNA

Question 2

RNA editing occurs in the 3 major classes of RNA

Answer 2

mRNA, tRNA, ribosomal RNA

Question 3

two classes of editing

Answer 3

insertion/deletion
modification (e.g. A to I, C to U, U to C)

Question 4

base modification

Answer 4

eg methylation
this is reversible
can change chemical properties of the base

Question 5

base modification

Answer 5

altered identity
flip purines (A to I (same as G))
ands flip pyrimidines (C to U)
via deamination

Question 6

effect of mRNA editing

Answer 6

eg
can create start and stop codons by inserting a U
(AUG - start)
can have a C and convert to a U
can change slice sites

Question 7

N6 - methyladenosine

Answer 7

methyl group added to an A (m6A)
regulated by writers (add methyl group), readers (recognise) and erasers (remove methyl group)

Question 8

writer example

Answer 8

Mettl3

Question 9

reader example

Answer 9

Hu-R, YTHDF1-3

Question 10

eraser example

Answer 10

FTP, AKLBH5

Question 11

what does it cause

Answer 11

hydrogen bond to U doesnt change
affects protein binding - sometimes reader protein only recognises the mRNA when its methylated or sometimes m6A blocks the reader protein

Question 12

m6A can make mRNA more stable which increases mRNA content and protein production or

Answer 12

it may cause a target for degradation of the mRNA so the mRNA level is decreased
depends on the mRNA and the protein it recruits as to the impact

Question 13

RNA editing by deamination (change one base for another)
cytosine deaminated is

Answer 13

uracil

Question 14

adenosine deaminated is

Answer 14

inosine (recognised as guanine)

Question 15

UAA is a common stop codon
is you change the C is CAA to a U you have a

Answer 15

stop codon
creates a smaller protein

Question 16

in the liver there is

Answer 16

no editing

Question 17

for example in the liver a protein called ApoB-100 is made (full length) contains an LDL-receptor binding site, in the intestine we have

Answer 17

editing so the protein so CAA is changed to UAA shorter protein ApoB-48 is made, this has no LDL-receptor binding. editing is carried out by the APOBEC-1 enzyme

Question 18

A to I change
edit in the Q/R site of the glutamate receptors

Answer 18

Q is changed to R after editing
occurs in L-glutamate major excitatory neurotransmitter
it normally lets sodium and calcium through
editing decreases the calcium permeability of the channels
signalling is reduced
editing carried out by ADAR2 gene

Question 19

RNA modification - ribose

Answer 19

methylation of 2 ribose from a OH group (2-0-methylation)
changes property of ribose
methylation stabilises 5’ end of DNA

Question 20

the nuclear pore

Answer 20

on nucleoplasmic side theres a cage structure
on cytoplasm site theres filaments
RNA is an acid meaning its charged and the pore is hydrophobic meaning RNA wont go through on its own

Question 21

tRNA export factor is

Answer 21

Exp-t

Question 22

miRNA (micro RNA) export factor is

Answer 22

Exp-5

Question 23

snRNA binds to cap binding complex (CBC) and has an export factor called

Answer 23

PHAX which binds CRM1 which exports proteins

Question 24

mRNA binds to CBC and ALY/Yra1 which binds to export proteins

Answer 24

TAP/Mex67 and p15/Mtr2

Question 25

rRNA is large so has lots of export adapters and export proteins

Question 26

why localise mRNA

Answer 26

localised protein synthesis
prevents expression in the wrong place

Question 27

diffusion based-localisation

Answer 27

protein bound to mRNA binds to anchor proteins at the site you want them to be so mRNA diffuses with the them