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Unformatted text preview: • One gene encodes one polypeptide
• Mutations in genes can lead to single amino acid substitutions in
• 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
• Hypothesis: the genetic code is read as a triplet code
– Deletion or addition of a single nucleotide...
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