Translation

Question 1

what occurs in the cleft of tRNA synthetase

Answer 1

• glycine gains AMP from a ATP molecule - aminoacyl-adenylate
• this then binds to a tRNA molecule which produces aminoacyl-tRNA

Question 2

what are the positions in mRNA which are used by tRNA 30S subunit

Answer 2

Aminoacylated tRNA binding site (A)
Polypeptide chain site (P)
Exit site (E)

Question 3

how is a peptide bond formed during translation elongation

Answer 3

• a protein chain attached to the original tRNA is attached to the P site
• A ‘charged’ tRNA binds to the A site
• Then a peptide bond is formed
• The protein chain is shifted to the newest tRNA (P site) by Elongation factor G (GTP) which binds to A site
• Old tRNA is moved to the E site and released

Question 4

what occurs to elongation factor G when it binds to A site

Answer 4

GTP -> GDP

Question 5

what is elongation factor G in eukaryotes

Answer 5

eEF2

Question 6

how does the 5’CAP initiate translation

Answer 6

Small subunit binds the CAP, then scans/move to the first AUG -encoding the initiating methionine

Question 7

what is the most frequently found sequence around the AUG in eukaryotic mRNA called

Answer 7

Kozak consensus sequence

Question 8

what are the function of elF4E subunit of the eIF4F complex

Answer 8

m7G binding

Question 9

what are the function of elF4G subunit of the eIF4F complex

Answer 9

binds eIF4E,A,3 PABP

Question 10

what are the function of elF4A subunit of the eIF4F complex

Answer 10

ATPase, RNA helicase

Question 11

what are the proteins needed for mRNA circularisation

Answer 11

eIF4E, G & PAB

Question 12

What is the first step of Translation initiation

Answer 12

• Ribosome recycling
  -> ABCE1, eIF3, eIF1A, EIF1
• 40S subunit is formed

Question 13

what is the 2nd step of translation initiation

Answer 13

eIF2 ternary complex formation
-eIF2 which contains GTP binds to Met-tRNA

Question 14

what is the 3rd step of translation initiation

Answer 14

43S preinitiation complex is formed where the 2 complex made in step 1 and 2 join

Question 15

what is the 4th step of translation initiation

Answer 15

attachment of 43S complex to activated mRNA (eIF4F complex already bound)

Question 16

what is the 5th step of translation initiation

Answer 16

5’ to 3’ scanning

Question 17

what is the 6th step of translation initiation

Answer 17

• Initiation codon recognition hydrolysis of eIF2-bound GTP and Pi release
• 48S initiation complex formed

Question 18

what is the 7th step of translation initiation

Answer 18

Subunit joining and factor displacement
- 60S + eIF5B (joined to GTP) join
- eIF2(+GDP), eIF5, eIF3, eIF1 is displaced

Question 19

what is the 8th step of translation initiation

Answer 19

Hydrolysis of eIF5B-bound GTP and release of eIF5B and eIF1A

Question 20

what is the final product of translation initiation

Answer 20

80S initiation complex

Question 21

How is translation terminated

Answer 21

• eRF1 binds to A site
• eIF3, eIF1, eIF1A and ABCE1 is released
• the ribosome is separated in 60S and 40S and mRNA and tRNA is released

Question 22

what is regulatory element of translation

Answer 22

eIF2B subunit of the eIF2

Question 23

how does eIF2B carry out its function

Answer 23

its level governs level of active eIF2-GTP and thus overall initiation rate

Question 24

eIF2B is down-regulated and phosphorylated in

Answer 24

• response to stresses such as viral infection, amino acid deprivation
  -diabetic muscle
  -heavy metals

Question 25

how is eIF2B activated

Answer 25

Insulin growth signals

Question 26

what regulates the expression of both Fe storage and transport proteins

Answer 26

levels of Fe

Question 27

what are UTR and where are they found

Answer 27

Untranslated regions 5'UTR - between CAP and AUG 3'UTR - between stop codon and polyA tail

Question 28

what occurs in low iron in terms of storage

Answer 28

IRP1/2 binds to 5'UTR causing translational repression

Question 29

what occurs in low iron in terms of transport

Answer 29

IRP1/2 binds to 3'UTR in both TfR1 and DMT1 whihc causes mRNA stabilisation

Question 30

what occurs to iron storage in high iron

Answer 30

4Fe-4s binds to IRP1 and IRP2 is degraded in the 5'UTR which causes translational activation

Question 31

what occurs to iron transport in high iron

Answer 31

4Fe-4s binds to IRP1 and IRP2 is degraded as well as degradation of probes using RNase in 3'UTR This causes mRNA degradation

Question 32

what is TfR1B

Answer 32

Canonical Iron response element

Question 33

what are IRE with additional 5' or 3' unpaired nucleotides

Answer 33

L-ferritin, DMT1 and HIF-2a

Question 34

IRP1 is a _ protein

Answer 34

bifunctional

Question 35

In absence of iron IRP1 functions as

Answer 35

an iron responsive protein 1

Question 36

In the presence of Fe and Fe-S cluster assembly enzymes IRP1 turns into

Answer 36

c-aconitase which interconverts citrate and isocitrate