BIO206H5 Lecture 13: Bio206 Lecture 22 October 2014

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31 Oct 2015
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Bio206 Lecture 22 October 2014
Eukaryotic Translation
Eukaryotic Initiation
Overall process resembles prokaryotic initiation
- more initiation factors (eIF-n) > 10
- tRNAiMet (initiator tRNA molecule) idiffers from regular tRNAMet but Met is not
formylated
- mRNA has different structure from prokaryotic
Stage 2:
- formation of 43s initiation complex
- includes the following
oeIF-1A
oeIF-3
o40s ribosome
omRNA
otRNAiMet + eIF-2
- number of different Initiation Factors
- how do u distinguish between IF from
eukaryotic and prokaryotic?
- Add “e” infront of it
- initiation complex for eukaryotes
- small ribosomal subunit is bound with
initiator tRNA
- mRNA have 5’ cap and poly- A tail
- mRNA is initially identified by eIF-4e
recognizes the 5’ cap and binds to the cap
- eIF4G also binds to 5’ cap
oalso poly-A tail is binded to
initiation complex
- initiation factors lines mRNA
correctly on small subunit
- small subunit and complex begin a
migration down mRNA
- initiation complex is scanning for
first AUG and trying to recognize
the Kozak consensus sequence
oCCRCCAUGG  R is any
purine (G/A)
- Complex wobbles down to recognize
kozak sequence
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- Initiation complex is positioned
on AUG of kozak sequence
- Ribosome can then begin being
built
- To add large 60s subunit the
initiation factors separate
- Large subunit then binds
- GTP energizes this process by
binding to eIF and the
hydrolysis is what drives the
reactions to forward direction
Elongation begins
With 3 stages
- charged tRNA in both A and P
site
-
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- different mechanisms that pro and euk have mRNA aligned on small subunit
Elongation
- sequential addition of amino acids with hydrolysis of bond to form peptide bond
- THIS IS CAYALYZED IN LARGE SUB UNIT OF RIBOSOMAL RNA
- Catalyzed by peptidyl
transferase 28s rRNA
located in large subunit
- cycling of elongation
- includes recylcling of
GTP+eEF-1A and eEF-1B
- eEF2 + GTP, eEF-1B, eEF-1A + GTP
othese are homologs of eukaryotic
elongation
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