2. The Genetic Code - Nov12

2. The Genetic Code - Nov12 - The Genetic Code Chem 431...

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The Genetic Code Chem 431 November 12 2009 Rebekah Nash
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DNA RNA Protein Nucleic Acids Nucleic Acids Amino Acids The Problem RNA Polymerase ??? Genetic Code tRNA Ribosome http://www.mcat45.com/content/dna-structure
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Definition The set of rules which dictates the  relationship between the base sequence  of a gene and the amino acid sequence of  its protein product DNA RNA Protein Nucleic Acids Nucleic Acids Amino Acids RNA Polymerase Genetic Code tRNA Ribosome
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The Code Table 32-2 The “Standard” Genetic Code a . Page 1290
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The Ground Rules 1. 3 nucleic acids/bases = 1 codon = 1  amino acid 2. Non-overlapping, no “comma’s” GUGCAUCUG… GUG CAU CUG GUG U CAU CUG 3. Degenerate
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Why 3 bases per codon? 4 bases vs. 20 amino acids 4^1 = 4 4^2 = 16 4^3 = 64 Result #1: since rule #2 holds…3 possible start points  = 3 possible reading frames GUG CAU CUG G UGC AUC UG GU GCA UCU G GUG CAU CUG V H L C I A S V H L
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Why 3 bases per codon? 4 bases vs. 20 amino acids 4^1 = 4 4^2 = 16 4^3 = 64 Result #1: 3 possible reading frames Result #2: Degeneracy Definition: multiple codons code for the same amino acid
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Example of Degeneracy 6 codons all code for the amino acid,  leucine: UUA, UUG, CUU, CUC, CUA, CUG  Protection against mutations Result of Degeneracy
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Sidetrack #1….types of  mutations 1. Frameshift Mutations Due to insertion or deletion of an entire base Result: changes reading frame and sequence Original sequence:  GUG CAU CUG Result of insertion:  GUG A CAU CUG … is read  GUG ACA UCU G… Result of deletion: 
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2. The Genetic Code - Nov12 - The Genetic Code Chem 431...

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