What encodes an amino acid how many nucleotides per

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Unformatted text preview: • One gene encodes one polypeptide • Mutations in genes can lead to single amino acid substitutions in proteins • Molecular diseases can be inherited Cracking The Genetic Code • How does DNA encode protein sequence? • What encodes an amino acid? – How many nucleotides per amino acid? – Is the code at all ambiguous? – How many “words” can encode each amino acid? Cracking The Genetic Code • What encodes an amino acid? – How does the cell know where to start and stop? – Is there punctuation within the code? – Is there overlap between “words”? – Is the code the same for all organisms? Cracking The Code • How can four nucleotides encode 20 amino acids? • Sidney Brenner - logically, what is the minimum “word” length that will allow encoding all 20? • One letter code: 4 “words” • Two letter code: 42= 16 “words” – Too few, unless the code is ambiguous • Three letter code: 43= 64 “words” • More than sufficient How Do You Prove It? • Crick, Brenner, and others: “frame-shift” mutations in bacteriophage • Hypothesis: the genetic code is read as a triplet code • Predictions: – Deletion or addition of a single nucleotide...
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This document was uploaded on 02/25/2014.

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