Uses a anticodon frequently it makes more of the

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uses a anticodon frequently it makes more of the  cognate   tRNA. This is  called codon bias . tRNAs are heavily modified after transcription Fig. 13-11, p. 296 BIO 1140 Unit 2-3: Translation 11
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61 different sense codons do  not  require 61 different tRNAs First two nucleotides of anticodon and codon must match exactly.  The third nucleotide has more flexibility. This discovery  lead to the “ Wobble Hypothesis Examples:  tRNA carrying phenylalanine matches codons  UUU & UUC tRNA  carrying leucine matches codons CUC and CUU tRNA carrying isoleucine matches codons AUU, AUC & AUA The Main Players in Translation: tRNAs Note: G-U,  I-U, I-C I-A BIO 1140 Unit 2-3: Translation 12
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Aminoacyl-tRNA synthetase charges the tRNA with  correct  amino-acid (adds amino acid to tRNA) the  aminoacyl-tRNA  is the name for the   amino acid  linked to tRNA  specificity of synthesis depends upon the anticodon  AND   OTHER BASES! There are ~20 such enzymes The Main Players in Translation:  Aminoacylation BIO 1140 Unit 2-3: Translation 13
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Made of ribosomal RNA (rRNA) and proteins Two subunits: Large and small Fig. 13-12, p. 297 The Main Players in Translation: Ribosomes BIO 1140 Unit 2-3: Translation 14
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Ribosomes consist of RNA and Protein Procaryote Eucaryote Size 70S (50S + 30S ) 80S (60S + 40S) Large  23S rRNA + 5S rRNA 28S rRNA + 5S rRNA Subunit  + “31” proteins ( L1..) + 5.8S rRNA  + “50”proteins  L1..) Small   16S rRNA  18S rRNA  Subunit + “21” proteins ( S1 ...) + “33” proteins ( L1 ..) You only need to memorize the information in blue. The Main Players in Translation: rRNAs BIO 1140 Unit 2-3: Translation 15
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Stages in Translation Initiation Ribosome assembled with mRNA molecule and  initiator methionine-tRNA Elongation Amino acids linked to tRNAs added one at a time to  growing polypeptide chain Termination New polypeptide released from ribosome Ribosomal subunits separate from mRNA BIO 1140 Unit 2-3: Translation 16
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Initiation  Initiator tRNA (Met-tRNA) binds to small subunit Complex binds to 5´ cap of mRNA, scans along  mRNA to find AUG start codon Large ribosomal subunit binds to complete initiation Little know fact: during translation the 5’ end and 3’ end  of the mRNA are in proximity!
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