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  1. translation initiation factors...
  2. what subunit & what site of the ribosome does the mRNA & initiator tRNA bind?
    • small subunit binds mRNA & tRNA
    • P site
  3. what is a Shine-Dalgarno sequence?
    typical sequence...
    • ribosome binding site (RBS) on the  mRNA
    • 5' AGGAGGU

    *the closer it matches the consensus seq. the more efficiently the mRNA will be translated
  4. non-overlapping vs. overlapping genes...
    • there is a shift of reading frame in overlapping genes (backwards)
    • non-overlapping has separate SD seq & protein-coding regions
    • overlapping genes can share SD & protein-coding regions overlap e.g. stop/start codon
  5. how does a Shine-Dalgarno seq. work?
    SD seq. base pairs w the 3' end of the 16S rRNA subunit of the small ribosomal subunit before the start codon
  6. why are there 2 tRNAs for Met & only 1 codon?
    • initiator = Met-tRNA^fMet = charged by methionyl-tRNA synthetase, then formyltransferase adds formyl group (H-O=C-) to amide N, so it can only be positioned at the start
    • Met-tRNA^mMet = internal positions => Met
  7. Prokaryote initiation factors (3)...

    function & binding
    • IF1 - blocks binding of initiator tRNA to A site
    • IF2 - GTPase that loads initiator tRNA to P site
    • IF3 - prevents premature binding btwn large & small ribosomal subunits

    The 30S binds IF1 & IF3, then mRNA
  8. what causes IF release?
    end product...
    • conformational change triggers IF3 release, large subunit binds, GTP hydrolysis cause IF2 release & IF1 releases
    • ...70S Initiation complex
  9. how does translation initiation differ in eukaryotes vs prokaryotes?
    • Eu
    • - NO SD site, so eIF4e bind 5' end cap
    • - NO formylation of Met, but still 2 diff tRNAs for initiaton vs internal AUG
  10. Eukaryotic initiation factors (6)...
    (prokaryotic equivalent)
    function & binding
    • eIF1A (IF1) - blocks A site
    • eIF1 - blocks E site
    • eIF3 (IF3) - prevents premature large & small subunit binding
    • eIF2 (IF2) - GTPase brings Met-tRNA^(i)Met to small subunit
    • eIF4F complex - mRNA assembly w 43S preinitiation complex
    • eIF5B - GTPase causes removal of factors allowing 40S + 60S = 80S ribosome
Card Set:
2014-11-21 05:03:06
Molecular Bio
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