Chapter32

Chapter32 - BCH 4054 Chapter 32 Lecture Notes Slide 1...

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Chapter 32, page 1 BCH 4054 Chapter 32 Lecture Notes Slide 1 Chapter 32 The Genetic Code Slide 2 Nature of the Genetic Code • Gene and protein structures are colinear • Tryptophan synthetase mutations (Yanofsky) • A cipher • Nucleotide sequence specifies amino acid sequence • Size of code must be 3 nucleotides/AA • 2 is not enough (4 2 = 16 “codewords”) • 3 is more than enough (4 3 = 64 “codewords”) • Insertion and deletion mutations support 3 • 3 insertions restore the reading frame • 3 deletions restore the reading frame Yanofsky in 1964 studied many mutations in tryptophan synthetase, mapping the distance of the mutations in the gene. He showed that the distances between the mutations were proportional to the distances between the amino acid substitutions in the protein. Slide 3 Nature of the Genetic Code, con’t. • Code is neither overlapping nor punctuated (See Fig 32.2). • Point mutations cause only 1 AA change. • 3 insertions or deletions restore reading frame. • Code is degenerate. • An amino acid can have more than one code word. • All codewords have meaning. • 3 of 64 stand for “terminate”, the remaining 61 code for one of the 20 amino acids. Also, the code is
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Chapter32 - BCH 4054 Chapter 32 Lecture Notes Slide 1...

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