DNA Translation

DNA Translation - DNA Translation How did scientists figure...

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DNA Translation How did scientists figure out whether codons were overlapping or non-overlapping? Inserted a mutation (single base substitution) and observed the synthesized proteins… if overlap, a single base would cause three mutations, but they observed only one amino- acid subtitution -> Genetic code is non-overlapping. READING FRAME: Any nuc sequence can be read in three different reading frames ORF, Open Reading Frame, is read between the start and stop codon. tRNAs have altered bases important in enzyme recognition. Has an acceptor stem ( CCA ) @ 3’ tail that is covalently bonded to an amino acid. -Antiparallel to mRNA (3’ of tRNA aligned w/ 5’ of mRNA and vice versa) -Sometimes AA is bound to 2’ sugar position of tRNA Ribosomes have no way of checking if tRNA is correctly matched w/ AA; are illiterate Aminoacyl-tRNA synthetase (ARS) charges the tRNA w/ the correct AA, resulting in aminoacyl-tRNA . -viz. seryl-tRNA is serine attached to tRNA -Most cells have 20 synthetases. Q: How do these enzymes recognize the correct tRNA? A: ARS looks for anticodons, yes, but there are 60+ anti-codons, so they must recognize another portion of the tRNA, such as the discriminator base nucleotide 73. Viz. seryl-tRNA synthetase must recognize six tRNA molecules which six different codons which are different from one another (because serine has six different codons) -An AA is covalently linked to tRNAs at the 2’ or 3’ OH by ARS, which is a reaction that requires ATP -has proofreading function and can remove incorrect AA
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This note was uploaded on 09/03/2010 for the course LS 252006132 taught by Professor Pham during the Summer '10 term at UCLA.

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DNA Translation - DNA Translation How did scientists figure...

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