2ALecture 14

Trnas carry weird modied nucleotides that promote

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Unformatted text preview: tRNA synthetases are a critical step in the genetic code! tRNAs carry weird, modified nucleotides that promote wobble base-pairing There are 20 synthetases–one for each aa But there are 61 codons. How many different tRNAs might each synthetase have to recognize? a.  Just 20, for 20 amino acids b.  61, because each codon needs the right anMcodon c.  Somewhere between 20 and 61, because of “wobble base pairs” No, please don’t memorize the details in this table Most tRNA synthetases have to recognize several different tRNAs Which synthetases clearly only have to recognize 1 tRNA? tRNA synthetases put the “translation” in translation Ribosomes just do base ­pairing 2 2/9/10 What’s a mutation? RNA polymerases mess up once in 1000 to 10,000 bases, and have no proofreading funcMon Can RNA polymerase cause mutaMons? Yes, if you’re a virus with an RNA genome. HIV (10,000 bases) gets a single base change with every round ­ If 1016 genomes of HIV are created on the planet every day ­ this means new beneficial* mutaMons arise every day! Drug ­resistant, etc What’s a mutation? tRNA synthetase has proofreading funcMon ­ if you feed it a mischarged tRNA it’ll remove the incorrect amino acid from the tRNA. Its net error rate (with proofreadin...
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