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Biochemistry 2280A
Christopher Brandl

Translation ● The decoding of the mRNAto produce a protein occurs on the ribosome Genetic Code ● mRNAspells out the amino acid code in 3 letter ‘words’called codons; each protein has a specific reading frame that is determined by where the decoding process begins The Code is: ● Universal (found in all organisms), nonoverlapping, commaless, no gaps (gaps were removed by splicing), 61 codons for 20 amino acids (therefore redundant), redundancy often occurs at the 3rd position of the codon (wobble), 3 stop codons and 1 star codon ● Also, the more common amino acids (found more often in proteins) have more codons, and related amino acids have similar codons ○ this is likely to reduce the possibility of major error in the final function of the protein; more codons for common amino acids means smaller chance of screwing up getting the wrong amino acid for a certain codon tRNA ● tRNAmolecules act as the vehicle that bring amino acids to the growing peptide chain; they function in a codon specific fashion relying on base pairing rules ● tRNAs tend to have a cloverleaf secondary structure and the anticodon of the tRNA hybridizes with the codon; the correct amino acid covalently links to 3’end of tRNA ● Wobble results from the fact that accurate base pairing for some tRNAs only requires matching at the first 2 positions AminoAcid Activation - Aminoacyl tRNAsynthetases ● UsingATP, carboxyl group of specific amino acid is coupled to 3’end of specific tRNA in high-energy bond; amino acid activation by aminoacyl t-RNAsynthetases important for: ○ providing energy source for later peptide bond formation ○ providing specificity b matching the correct amino acid to the specific tRNA Ribosomes ● Ribosomes have two subunits, large and small; both composed of rRNAand protein ● The small subunit matches tRNAs to the codons whereas the large subunit catalyzes the formation of peptide bonds ● There are 3 sites for tRNAs on the ribosome,Asite (aminoacyl tRNAsite), P site (peptidyl tRNA), and E site (exit site) ○ two of these sites are occupied at any one time; the mRNA is bound in proximity of theAand P site
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