1. Javad Jamshidi Fasa University of Medical Sciences, December 2015 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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11. 11 Some 30-40 different tRNAs have been identified in bacterial cells and as many as 50-100 in animal and plant cells. The number of tRNAs in most cells is more than the number of amino acids also differs from the number of amino acid codons in the generic code (6 4).

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13. 13 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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21. 21 A Polyribosome

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