Translation Flashcards
what occurs in the cleft of tRNA synthetase
- glycine gains AMP from a ATP molecule - aminoacyl-adenylate
- this then binds to a tRNA molecule which produces aminoacyl-tRNA
what are the positions in mRNA which are used by tRNA 30S subunit
Aminoacylated tRNA binding site (A)
Polypeptide chain site (P)
Exit site (E)
how is a peptide bond formed during translation elongation
- 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
what occurs to elongation factor G when it binds to A site
GTP -> GDP
what is elongation factor G in eukaryotes
eEF2
how does the 5’CAP initiate translation
Small subunit binds the CAP, then scans/move to the first AUG -encoding the initiating methionine
what is the most frequently found sequence around the AUG in eukaryotic mRNA called
Kozak consensus sequence
what are the function of elF4E subunit of the eIF4F complex
m7G binding
what are the function of elF4G subunit of the eIF4F complex
binds eIF4E,A,3 PABP
what are the function of elF4A subunit of the eIF4F complex
ATPase, RNA helicase
what are the proteins needed for mRNA circularisation
eIF4E, G & PAB
What is the first step of Translation initiation
- Ribosome recycling
-> ABCE1, eIF3, eIF1A, EIF1 - 40S subunit is formed
what is the 2nd step of translation initiation
eIF2 ternary complex formation
-eIF2 which contains GTP binds to Met-tRNA
what is the 3rd step of translation initiation
43S preinitiation complex is formed where the 2 complex made in step 1 and 2 join
what is the 4th step of translation initiation
attachment of 43S complex to activated mRNA (eIF4F complex already bound)
what is the 5th step of translation initiation
5’ to 3’ scanning
what is the 6th step of translation initiation
- Initiation codon recognition hydrolysis of eIF2-bound GTP and Pi release
- 48S initiation complex formed
what is the 7th step of translation initiation
Subunit joining and factor displacement
- 60S + eIF5B (joined to GTP) join
- eIF2(+GDP), eIF5, eIF3, eIF1 is displaced
what is the 8th step of translation initiation
Hydrolysis of eIF5B-bound GTP and release of eIF5B and eIF1A
what is the final product of translation initiation
80S initiation complex
How is translation terminated
- 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
what is regulatory element of translation
eIF2B subunit of the eIF2
how does eIF2B carry out its function
its level governs level of active eIF2-GTP and thus overall initiation rate
eIF2B is down-regulated and phosphorylated in
- response to stresses such as viral infection, amino acid deprivation
-diabetic muscle
-heavy metals
how is eIF2B activated
Insulin
growth signals
what regulates the expression of both Fe storage and transport proteins
levels of Fe
what are UTR and where are they found
Untranslated regions
5’UTR - between CAP and AUG
3’UTR - between stop codon and polyA tail
what occurs in low iron in terms of storage
IRP1/2 binds to 5’UTR causing translational repression
what occurs in low iron in terms of transport
IRP1/2 binds to 3’UTR in both TfR1 and DMT1 whihc causes mRNA stabilisation
what occurs to iron storage in high iron
4Fe-4s binds to IRP1 and IRP2 is degraded in the 5’UTR which causes translational activation
what occurs to iron transport in high iron
4Fe-4s binds to IRP1 and IRP2 is degraded as well as degradation of probes using RNase in 3’UTR
This causes mRNA degradation
what is TfR1B
Canonical Iron response element
what are IRE with additional 5’ or 3’ unpaired nucleotides
L-ferritin, DMT1 and HIF-2a
IRP1 is a _ protein
bifunctional
In absence of iron IRP1 functions as
an iron responsive protein 1
In the presence of Fe and Fe-S cluster assembly enzymes IRP1 turns into
c-aconitase which interconverts citrate and isocitrate
