tRNA charging.txt

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  1. Definition of tRNA charging
    aka aminoacylation of tRNA: the process by which the correct amino acid is attached to its cognate tRNA.
  2. Enzyme which catalyzes tRNA charging
    aminoacyl-tRNA synthase (RS)
  3. t-RNA charging reaction facts
    • 1. A single RS is used for each for each amino acid..recognizing different nucleotides of the 4 arms and variable loop of tRNA, aka '2nd operational genetic code'
    • 2. ATP is needed to provide energy for the reaction
    • 3. aa (amino acid) gets attached to the acceptor arm by a specific RS
    • 4. Aminoacyl-AMP (Aa-AMP) intermediate is formed during the charging process.
  4. tRNA molecule and binding sites
    • tRNA is a small molecule (~80 Nt residues) that is t-shaped
    • w/ 4 arms ( D arm, anticodon arm, TΨC arm, & acceptor arm)
    • w/ variable loop
  5. RS recognizing specific AA
    • RS can recognize the active site pocket (how aa fits into ligand pocket)
    • Class I, aa interacts with KMSK and HIGH motifs
    • RS makes sure aa is able to form bonds to metal cations
    • RS can remove BAD AA after charging
  6. Class I aminoacyl-tRNA synthetase
    • Class I: aa-AMP first attaches to C-2 (carbon of OH ribose sugar) & transferred via transesterification to C-3
    • It is specific for 10 aa
    • mainly a MONOMER
    • active site SHORT (170 aa)
    • active site on LEFT side of RS
    • RS approaches tRNA acceptor end from MINOR groove
    • Uses Zn binding domain
    • Contains Rossman fold motif & uses KMSK & HIGH motifs in active site for charging aa
  7. Class II aminoacyl-tRNA synthetase
    • aa-AMP attached to C-3 (3rd carbon OH-ribose sugar)
    • specific for 10 aa
    • mainly a DIMER
    • active site LARGE (250aa)
    • active site located on RIGHT side of RS
    • RS approaches tRNA acceptor end from MAJOR groove
    • Contains motifs 1, 2 & 3
  8. Editing in aminoacyl-tRNA synthetases (RS's)
    • Type 1: before Aa-charging editing (pre-transfer editing)
    • 1. Aa-AMP intermediate is formed
    • 2. Aa-AMP is checked if it fits in the editing site
    • 3. if Aa-AMP DOES NOT fit, it is kept(correct Aa)
  9. Editing: if Aa-AMP DOES fit..
    • is removed (bad AA)
    • 1. Correct Aa-AMP is attached to tRNA, (eventually the AMP is removed
  10. Type 2: after Aa-charging editing (post-transfer editing)
    • 1. Aa-AMP intermediate is formed
    • 2. Bad Aa-AMP is attached to tRNA (eventually the AMP is removed
    • 3. Bad Aa-tRNA is checked into editing site
    • Bad Aa is removed (bad AA)
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tRNA charging.txt
2012-03-20 10:56:11

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