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| Can mRNA tell if the aa is wrong? |
-NO
-The Ribosome Is Unable to Discriminate between Correctly and Incorrectly Charged tRNAs |
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mcs5109 Thu, 23 Oct 2008 01:45:40 GMT |
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| Are tRNAs accurate? |
YES, ma'am.
-tRNA synthetases proofread, too
-<1 in 1,000 have errors
-Some enzymes “check” the amino acid at the aminoacyl-adenylate intermediate. If incorrect, hydrolyzed
-other enzymes “check” the aminoacyl-tRNA product, and cleave off incorrect amino acids
-Use editing pocket in enzyme |
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mcs5109 Thu, 23 Oct 2008 01:45:40 GMT |
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how do tRNA synthetases know they have the right aa?
b/c CCA on all? |
-anticodon!
-acceptor stem!
-both!
-if >1 codon for aa, synthetase must rely on determinants outside of the anticodon |
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mcs5109 Thu, 23 Oct 2008 01:41:22 GMT |
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| Some bacteria have __ tRNA sythetases |
<20
-why?
-b/c they have an enzyme which modifies a charged tRNA to another aa form
-ex:
Glu-tRNAGln -> (amination) -> Gln-tRNAGln
-recognizes Gln, but attached Gln |
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mcs5109 Thu, 23 Oct 2008 01:34:37 GMT |
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| Most organisms have __ different tRNA synthetases |
(only one tRNA synthetase attaches each amino acid) |
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mcs5109 Thu, 23 Oct 2008 01:34:37 GMT |
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| isoaccepting tRNAs |
-aminoacyl tRNA synthetase recognizes and charges more than one tRNA (b/c >1 codon for most aas) |
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mcs5109 Thu, 23 Oct 2008 01:34:37 GMT |
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| What's the driving force of tRNA synthetase? |
-pyrophophotase cleaves pyrophosphate (PP) to prevent reverse reaction |
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mcs5109 Thu, 23 Oct 2008 01:23:35 GMT |
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| there are ___ classes of tRNA Synthetases |
2 |
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mcs5109 Thu, 23 Oct 2008 01:23:35 GMT |
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| adenylyation |
-adding AMP |
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mcs5109 Thu, 23 Oct 2008 01:23:35 GMT |
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| 2 steps of Aminoacyl tRNA Synthetases |
1. aa is activated by adenylylation (adding AMP)
2. Activated aa is transferred to the 2’ or 3’ OH of the adenosine of tRNA (release of AMP)
There are two classes of tRNA synthetases
Driving force: pyrophophotase cleaves pyrophosphate to prevent reverse reaction. |
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mcs5109 Thu, 23 Oct 2008 01:23:35 GMT |
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| Aminoacyl tRNA Synthetases work in ___ steps |
2 |
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mcs5109 Thu, 23 Oct 2008 01:23:35 GMT |
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| how to charge tRNA? |
Aminoacyl tRNA Synthetases |
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mcs5109 Thu, 23 Oct 2008 01:13:18 GMT |
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| energy situation of the ribosome |
-Ribosomes use a lot of GTP hydrolysis, but only to increase translational accuracy
-no energy needed for making/breaking bonds |
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mcs5109 Thu, 23 Oct 2008 01:13:18 GMT |
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| acyl linkage |
-how the aa is linked to tRNA
-between the aa carboxyl group and the 2’- or 3’-OH group of A
-5’-CCA-3’
-high-energy bond
-thermodynamic energy to drive protein synthesis,
therefore, ribosome doesn’t need extra energy
(Ribosome and its translation factors use a lot of GTP hydrolysis, but all of them to increase translational accuracy) |
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mcs5109 Thu, 23 Oct 2008 01:13:18 GMT |
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| charged tRNA |
-tRNA molecule with aa attached |
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mcs5109 Thu, 23 Oct 2008 01:13:18 GMT |
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| FAT L |
SigmaU loop + aa acceptor stem
D stem + anticodon arm
-aa acceptor stem is maximally separated from the anticodon loop |
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mcs5109 Thu, 23 Oct 2008 01:08:09 GMT |
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| Why the D loop? |
-Reduction of a double bond in uridine gives dihydrouridine, “D” |
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mcs5109 Thu, 23 Oct 2008 01:08:09 GMT |
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| 4 loops of tRNA |
-variable loop
-anticodon loop
-D loop
-SigmaU loop (TsigmaC loop) |
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mcs5109 Thu, 23 Oct 2008 01:08:08 GMT |
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| post-transcriptional bases in tRNA |
-not essential for tRNA function
-but, reduce growth for cells lacking these bases
-show improved tRNA function |
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mcs5109 Thu, 23 Oct 2008 01:08:08 GMT |
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| do tRNA have the usual base? |
-and more!
-created post-transcriptionally
-not essential for tRNA function…
…but cells lacking these modified bases show reduced rates of growth
…improved tRNA function |
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mcs5109 Thu, 23 Oct 2008 01:08:08 GMT |
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| How does 5’-CCA-3’ get on euk tRNA? |
-CCA polymerase |
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mcs5109 Thu, 23 Oct 2008 01:08:08 GMT |
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| sequence to attach cognate aa in tRNA |
5’-CCA-3’
-universally conserved
- |
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mcs5109 Thu, 23 Oct 2008 01:08:08 GMT |
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| how many nucleotides in tRNA? |
75 to 95 nucleotides |
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mcs5109 Thu, 23 Oct 2008 01:08:08 GMT |
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