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Biological Sciences
Aarti Ashok

Translation I Encoding Genetic Information  how is the info in nucleic acids (DNA, then mRNA) converted into the order of amino acids incorporated to build a protein? o Genetic code  discovered that 3 nucleotides likely specified the ‘code’ for a single amino acid o these nucleotides or codons are non-overlapping  examining the outcome of diseases such as sickle cell anemia (single base substitution) revealed that the code is non-overlapping   only affected one amino acid = one codon o the genetic code is degenerate  64 possible codons encode 20 amino acids and ‘stop’  more than one codon per type of amino acid  BUT what does each codon specify? Identifying the codons  Marshall Nirenberg and colleagues synthesized an mRNA in vitro solely made up of U’s  poly(U)  Incubated this with bacterial extract (contains all amino acids and factors necessary for protein synthesis)  Examined the new polypeptide synthesized  it was polyphenylalanine  Therefore UUU codon = phenylalanine  By similar methods, the coding specificities of each of the 64 codons was discovered The genetic code deciphered  Mitochondrial mRNAs and transcripts in some protists and fungi are not translated according to this standard code  some deviations exist in nature Properties of the genetic code  codons for a specific amino acid tend to be clustered within a particular region of the chart o similarity of codons that encode the same amino acid o protects from some spontaneous mutations  similar amino acids tend to be encoded by similar codons - ex. hydrophobic amino acids o base substitution would lead to incorporation of an amino acid with similar properties  greatest similarity b/w codons for the same amino acid is in the first 2 nucleotides; greatest variability in
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