PPP_Ch 14 - CHAPTER 14 Genetic Code and Transcription Dr...

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CHAPTER 14 Genetic Code and Transcription Dr. Sanghamitra Mohanty
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Focus of this chapter: 1) Genetic code Basic characteristics of genetic code Deciphering the code Wobble hypothesis Exceptions to the rules of genetic code 2) Transcription Prokaryotic and Eukaryotic transcription
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The genetic code is written in linear form, using the ribonucleotide bases that compose mRNA molecules as “letters.” The sequence of RNA is derived from the complementary bases in the DNA.
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In the mRNA, triplet codons specify one amino acid. The code contains “start” and “stop” signals, certain codons that are necessary to initiate and to terminate translation . .
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The genetic code is: unambiguous degenerate commaless nonoverlapping nearly universal
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mRNA serves as an intermediate in transferring genetic information from DNA to proteins. The triplet code provides 64 codons to specify the 20 amino acids. The triplet nature of the code was revealed by frameshift mutations ( Figure 14.2 ).
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The genetic code reads three nucleotides at a time in a continuous, linear manner. Thus, the code is nonoverlapping and comma-less . The genetic code is degenerate , which means that some amino acids are specified by more than one codon. The nonsense codons do not specify an amino acid.
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An in vitro protein synthesizing system along with the ability to produce synthetic mRNAs using polynucleotide phosphorylase provided the means for deciphering the genetic code.
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Nirenberg and Matthaei added RNA homopolymers to the in vitro translation system to decipher which amino acids were
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PPP_Ch 14 - CHAPTER 14 Genetic Code and Transcription Dr...

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