1. Javad Jamshidi Fasa University of Medical Sciences, December 2014 Genetic Codes and Transcription

2. 2 How is the information in a linear sequence of nucleotides in RNA translated into the linear sequence of a chemically quite different set of units-the amino acids in proteins?

3. 3 The language is not the same Nucleotides vs. Amino acids An intermediate (tRNA) The number of letters are not the same 4 Nucleotides vs. 20 Amino acids Combinations of three nucleotides

4. 4 There are 20 amino acids 1 nucleotide for 1 AA = 4 2 nucleotide for 1 AA = 4 2 = 16 3 nucleotide for 1 AA = 4 3 = 64 Each genetic code is a consecutive groups of three nucleotides Some amino acids are specified by more than one triplet The genetic code is used universally in all present-day organisms, with some exceptions

5. 5 This code was deciphered by Marshall Nirenberg and his colleges in 1961

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7. Reading Frame

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12. 12 Each tRNA molecule becomes linked to the one amino acid in 20 that is its appropriate partner Recognition and attachment of the correct amino acid depends on enzymes called aminoacyl-tRNA synthetases Most cells have a different synthetase enzyme for each amino acid (that is, 20 synthetases in all) The aminoacyl-tRNA synthetase enzymes and the tRNAs are equally important in the decoding process

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20. 20 A Polyribosome

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