BIO40-19 Gene...c Code Handou

BIO40-19 Gene...c Code Handou - • Contains punctuation...

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What is the genetic evidence for the triplet nature of the code? Crick et al. early 1960s rII x (mutant) -> large, clear plaques -> do not grow on K12 rII + (WT) -> small, turbid plaques -> grow on K12 E. coli strain B rII + (WT) proflavin treatment (mutagenized) rII x (mutant) proflavin treatment (mutagenized) rII y Revertant WT (back mutation)? or double mutants? E. coli strain K12 rII z Revertant rII y Revertant X rII + WT (coinfected B) E. coli strain B two possible results
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Features of the genetic code. Linear: The code is written in linear form using the ribonucleotide bases that compose mRNA molecule as letters. Unambiguous: Each triplet specifies only one amino acid. Degenerate: More than one triplet specifies a given amino acid. Ordered: Codons for a single aminoacid are generally grouped together, varying only the third base.
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Unformatted text preview: • Contains punctuation signals: “Start” (AUG) initiates translation while “stop” (UAA, UAG, UGA) terminates translation. • Commaless: No internal punctuation is used. • Non overlapping: Every single nucleotide at a specific location within the mRNA is part of only one triplet. • Almost universal: With only minor exceptions, a single coding dictionary is used by almost all viruses, prokaryotes, and eukaryotes. The most important exceptions to the universality of the genetic code occur in mitochondria of mammals, yeast, and other species. In mitochondria: 1. UGA specifies tryptophan rather than stop. 2. AUA is a methionine codon, not an isoleucine codon. 3. AGA and AGG are chain termination codon rather than arginine codons....
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BIO40-19 Gene...c Code Handou - • Contains punctuation...

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