Chapter 13 - Genetic Code and Transcription

Chapter 13 - Genetic Code and Transcription - Chapter 13...

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Chapter 13 The Genetic Code and Transcription Genetic Code Exhibits Number of characteristics - genetic code written in linear form - each word contains three ribonucleotide letters o codon specified one amino acid, group of three nucleotides - code is unambiguous each codon specifies only a single amino acid - code is degenerate given amino acid can be specified by more than one codon - code contains start and stop signals (initiation and termination) for translation - code is commaless no internal punctuation used in the code - code is nonoverlapping any single ribonucleotide at a specific location within the mRNA is part of only one codon after translation - code is universal single coding dictionary is used by almost all viruses, prokaryoted, archaea, and eukaryotes Early Studies Established the Basic Operational Patterns of the Code - triplet nature of the code o frameshift mutations insertion or deletion of a single nucleotide which causes the frame of reading to shift, whereby the specific sequence of all subsequent downstream codons are changed - nonoverlapping nature of the code o adaptor molecule molecule proposed by Crick to covalently bind to amino acid and to the amino acid - commaless and degenerate nature of the code o nonsense codons blank codons that did not specify to amino acids Studies by Nirenberg, Matthaei, and Others led to Deciphering the Code - synthesizing polypeptides in a cell-free system o cell-free system for protein synthesis and availability of synthetic mRNAs provided a means of deciphering the ribonucleotide composition of
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Chapter 13 - Genetic Code and Transcription - Chapter 13...

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