lecture 9

Question 1

prokaryotic ribosome is

Answer 1

70S (large subunit (50S) small subunit (30S))

Question 2

eukaryotic ribosome is

Answer 2

80S (large subunit (60S) small subunit (40S))

Question 3

A,P and E sites

Answer 3

tRNA comes in and slots into A (aminoacylated tRNA binding site) site
everything shifts due to the elongation factor and the peptide chain is handed over to the new tRNA with the new amino acid on the P site (polypeptide chain site)
and old tRNA moves to the E (exit) site

Question 4

m7G cap and poly A are key for translation

Answer 4

Cap is not next to the start codon
cap binding to the small subunit of the ribosome is the start of translation
small subunit scans till the first AUG then it starts translation

Question 5

sequence in front of AUG is the

Answer 5

kozak consensus - CC(A/G)CC
is improves translation initiation

Question 6

once the small subunit has found the start codon the

Answer 6

large subunit comes in

Question 7

eIF4F complex comes in which contains

Answer 7

eIF4E, G and A

Question 8

eiF4F complex comes in and binds to the cap

Answer 8

activates mRNA

Question 9

the poly A tail is bound by PABP (poly A binding protein) which comes round and binds to the

Answer 9

eIf4F complex

Question 10

mRNA is circularised, supposed to help the ribosome come back to the cap

Answer 10

eIF4G is what links with the PABP
eIF4A is a ATPase and RNA helicase which opens up structure before the AUG to allows the small subunit to scan along so not blocking

Question 11

small subunit is bound to eIF2 which is a GTPase which forms the preinitiation complex with tRNA

Answer 11

then preinitiation complex binds with activated mRNA

Question 12

small subunit starts scanning along for AUG

Answer 12

then once recognised hydrolysis of eIF2 bound GTP and phosphate release (48S initiation complex)

Question 13

eIF2 then leaves and then 60S subunit comes in with eIF5B (GTPase)

Answer 13

rest of initiation factors leave and we have a full ribosome
hydrolysis of eIF5B GTP and release of eI5FB

Question 14

elongation

Answer 14

next tRNA comes in with eEF1A coupled with GTP
and tRNA docks in the A site

Question 15

then theres peptide bond formation between

Answer 15

the two amino acids

Question 16

eEF2 comes along and helps

Answer 16

translocation on the mRNA, allowing next tRNA to come in

Question 17

termination

Answer 17

when it gets to stop codon eRF1 comes in and sits in the A site
peptide is release from tRNA and eRF1 is released and with eRF3 and other factors the 2 ribosome subunits are pulled apart and theyre are recycled

Question 18

regulation of translation:
eIF2B

Answer 18

involved in bringing the initiation tRNA to the small subunit
eIF2 in the subunit and eIF2B in one of the proteins
eIF2B level governs the level of active eIF2-GTP and thus overall initiation rate
eIF2B down regulated in response to stresses such as viral infection, amino acid deprivation. therefore translation is shut down
eIF2B is also activated by insulin

Question 19

inactivation of eIF2 by phosphorylation

Answer 19

phosphorylation is of eIF2B –> general translation blockade

Question 20

we still need to produce certain proteins during stress

Answer 20

we get stress specific mRNAs

Question 21

iron requlation

Answer 21

iron regulates the expression of iron storage/transport proteins

Question 22

low iron

Answer 22

storage proteins -don’t need them so theyre repressed
IRP 1/2 binds to region in 5’ UTR leads to translational repression
transport proteins - upregulated
IRP 1/2 binds to region in the 3’ UTR causes mRNA stabilisation –> more RNA in the cell therefore more transport proteins

Question 23

IRP =

Answer 23

iron responsive proteins

Question 24

UTR - untranslated region

Answer 24

5’ UTR - between start codon and m7G cap
£’ UTR - between stop codon and poly A

Question 25

high iron

Answer 25

need more storage proteins to keep iron levels down in the cell
iron binds to IRP1
IRP2 is degraded when its not bound
so no binding to the 5’ UTR and no repression of the storage proteins
and no binding to 3’ end so degradation of the transport proteins

Question 26

IRP1is a bifunctional proteins as it is also

Answer 26

c-aconitase
when theres low iron levels it becomes IRP1 so it can bind to RNA to down regulate storage proteins and upregulate transport proteins
in the presence of iron is becomes c-aconitase and converts citrate to isocitrate in the mitochondria