initiation of eukaryotic translation Flashcards
how does initiation of eukaryotic translation differ from that of prokaryotes?
- there is no shine-delgarno recognition
- the 40S binds to the mRNA cap via protein-protein interactions rather than directly to the initiation codon via RNA-RNA
what is the structure of eukaryotic mRNAs?
capped at 5’ end, tailed at the 3’ end. they have a single coding sequence, and a 5’ and 3’ untranslated region which commonly forms secondary structures
what is the structure of the cap on mRNA?
a GTP residue, modified at position 7 on the G base and flipped around to produce a 5’ triphosphate and 3’ OH at the 5’ terminus
what is attached at the end of the 3’ tail?
poly-A blinding proteins
how is the pre-initation complex (43S) formed?
initiator tRNA is picked up by IF2, which binds the small ribosomal subunit.
where does the PIC bind?
to the cap of the mRNA, this is an ATP consuming process
how is the PIC held to the cap?
the interaction between eIF3 and eIF4
in which direction does the PIC migrate?
5’-3’ until it finds the start codon
which eIF does the process of scanning depend on?
eIf1 - keeps the scanning complex open and and capable of scanning
which eIF provides energy for the scanning process?
eIF4A - this has Helicase/ATPase activity which provides the energy for scanning by unwinding mRNA ahead of the scanning complex
when does scanning end?
when the PIC finds the AUG at the start of the ORF
what happens when factor 1 leaves the PIC?
factor 5 assumes its position, this triggers GTPase activity for factor 2
the departure of which eIFs causes the 43S complex to close?
- 1
- 2
- 5
what does the transition from 43S to 48S complex allow?
the initiator aminoacyl-tRNA can recognise the initiation codon, permitting protein synthesis to start
what does the 48S initiation complex consist of?
factors 4,3,1a, 5b
