lecture 7 - post transcriptional control of gene expression

Question 1

DNA –>RNA –> PROTEIN

Answer 1

DNA is LUCA (last universal common ancestor)

Question 2

eukaryotes

Answer 2

mRNA has to get into cytoplasm to be translated
different to prokaryotes as theres no membrane bound compartments in them

Question 3

DNA goes to primary RNA transcript then to mRNA

Answer 3

mRNA passes through nuclear pore and gets translated
regulation is possible as each step

Question 4

eukaryotic mRNA components

Answer 4

start codon (AUG) and stop codon
at the 5’ end theres a m7G cap structure
at 3’ end theres a poly A tail

Question 5

the m7G cap and poly A tail arent transcribed as they are added

Answer 5

after transcription

Question 6

the unfinished mRNA is known as

Answer 6

pre-mRNA

Question 7

4 events that occur to the pre-mRNA

Answer 7

capping
splicing
polyadenylation
editing

Question 8

CTD (c terminal domain) on the RNA pol II recruits factors required for capping splicing polyadenylation and editing making these events coupled to

Answer 8

transcription

Question 9

capping

Answer 9

RNA initially contains triphosphate at the 5’ end
triphosphate is modified

Question 10

first step

Answer 10

a G nucleotide is added onto 5’ end
theres 3 phosphates between the ribose groups
and the chain runs 5’ to 3’ but his is running 5’ to 5’

Question 11

second step

Answer 11

the G get methylated which changes the behaviour of the base

Question 12

functions of the m7G cap

Answer 12

protects mRNA from degradation by nucleases
facilitates splicing
facilitates export from the nucleus
critical for translation

Question 13

cap works through binding proteins

Answer 13

(binds to CBP80/CBP20 in the nucleus)
(binds to el54 in the cytoplasm)

Question 14

splicing

Answer 14

exons - coding sequences
introns - non coding
pre-mRNA contains transcribed introns and exons
splicing - exons join together to get a continuous open reading frame

Question 15

intron and exon boundaries contain conserved sequences

Answer 15

have a 5’ splice site
a 3’ splice site
a branch site in the middle

Question 16

reaction: 2 trans-esterification reactions
step 1

Answer 16

cut at 5’ SS
create a bond between 5’ end of intron and branch site

Question 17

step 2

Answer 17

cut at 3’ splice site and release intron lariat
exons ligate together
intron is degraded

Question 18

whats doing the splicing

Answer 18

a enzyme complex called the spliceosome
catalyses the removal on introns and ligation of exons
requires ATP

Question 19

proteins in the spliceosome include

Answer 19

RNA- binding proteins
ATPases
GTPases

Question 20

complex contains snRNPs

Answer 20

small nuclear ribonucleo-protein particles
RNA doesnt code for protein
RNAs base pair with conserved sequences in the intron (U1 with the 5’ SS, U2 with the branch point)
splicing is catalysed by the snRNAs

Question 21

snRNAs fold up (U1-4) and they have an Sm binding site

Answer 21

Sm binding site - A/G AUUUUUG A/G
snRNAs pass through the middle of the Sm protein structure
snRNP is one of these snRNAs and the set of proteins

Question 22

people with systemic lupus erythematosus produce antibodies against the

Answer 22

Sm proteins

Question 23

firstly U1 binds to the 5’SS then

Answer 23

U2 binds to the branch point

Question 24

the U4,5 and 6 come in together and join and U1 and U4 are kicked out. U6, 2 and 5 carry out step 1 and step 2

Answer 24

snRNPs are released so they can be used again and intron is released and degraded
snRNA binds to the conserved sequences by base paring

Question 25

any exon can join to any other exon - not linear

Answer 25

celled alternative splicing
80% of our gene undergo this

Question 26

we have more different proteins in our cells than we have genes

Answer 26

this is due to alternative splicing

Question 27

mutations in splicing

Answer 27

mutations in splice site and the exon gets skipped
mutations can cause reduces isoform of a protein

Question 28

polyadenylation

Answer 28

addition of poly A tail
AAUAAA in mrna is a cleavage site for endonuclease from the RNA
then you get addition of As by polyA polymerase

Question 29

upstream of the AAUAAA is USE (U-rich upstream element)
down stream is the G/U rich tract

Answer 29

between G/U tract and AAUAAA is where the poly site is

Question 30

proteins required for polyadenylation binds to these sequences

Answer 30

CPSF binds to AAUAAA
CstF binds to G/U
PolyA polymerase (adds tail)

Question 31

poly a tail

Answer 31

enhances export of RNA
stabilises 3’ end
enhances translation of mRNA