110C LEC 12 Translation 1

110C LEC 12 Translation 1 - BCH 110C LECTURE 12 Translation...

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BCH 110C LECTURE 12 Translation 1 Lodish 6 th ed. Chapter 4.3; Pages 132-133
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Where are we?
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Specific RNA • Ribosomal RNA is transcribed by Polymerase I in the nucleolus producing 28S, 5.8S and 18S rRNA • Polymerase III produces tRNAs coding for 20 amino acids and 5S rRNA • Polymerase II transcribes all mRNA RNA, small nuclear RNA involved in splicing and regulatory RNA microRNA (miRNA) & small interfering RNA (siRNA) Tandemly repeated genes • rRNAs, tRNAs, histone mRNAs • Repeated genes provide the high levels of these RNAs required • 60S large ribosomal subunits consist of 28S, 5.8S, and 5S rRNA and 50 different proteins • 40S small ribosomal subunits consists of 18S rRNA and 33 proteins Protein synthesis related RNA
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Features of the Genetic Code • A codon is made up of 3 consecutive bases in an mRNA
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Features of the Genetic Code • 4 possible nucleotides used in each of 3 positions = 4 4 4=64 possible code “words” • 1 codon codes for “START” [AUG=Met] • 3 codons code for “STOP” • 61 codons code for the 20 (22) amino acids
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The Genetic Code Met Don’t memorize stop codons
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The Genetic Code is Degenerate
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tRNA is an adaptor between RNA sequence and amino acid sequence • ~80 nucleotides • Very similar secondary and tertiary structures • Differ somewhat in primary sequence • Human has 497 tRNA genes of 48 different kinds 1 position of the codon base pairs to the 3 position of the anticodon One amino acid attached here
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Clover leaf representation of tRNA
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Properties of tRNA • ~Half the bases are intra-strand base paired • All contain modified bases • 5’ end usually G • 3’ end is CCA-3’ • 3’ end is amino acid attachment site
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All tRNA have modified bases Function Stabilize against degradation Recognition sites for translation factors
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There are fewer tRNA kinds than there are codons • 48 different tRNAs decode 60
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110C LEC 12 Translation 1 - BCH 110C LECTURE 12 Translation...

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