Topic 12B - Translation S10 1pp

Topic 12B - Translation S10 1pp - From Gene to Protein...

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From Gene to Protein Topic 12 Part B - Translation Chapter 17
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TRANSLATION • Translation is the RNA-directed synthesis of a polypeptide • A cell translates an mRNA message into protein with the help of transfer RNA (tRNA) • Molecules of tRNA are not identical: – Each carries a specific amino acid on one end – Each has an anticodon on the other end; the anticodon base-pairs with a complementary codon on mRNA
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Fig. 17-13 Polypeptide Ribosome Amino acids tRNA with amino acid attached tRNA Anticodon T r p P h e Gly Codons 3 5 mRNA
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A C C • A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long • Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a cloverleaf • Because of hydrogen bonds, tRNA actually twists and folds into a three- dimensional molecule – tRNA is roughly L-shaped Amino acid attachment site 3 5 Hydrogen bonds Anticodon (a) Two-dimensional structure Amino acid attachment site 5 3 Hydrogen bonds 3 5 Anticodon Anticodon (c) Symbol used in this book (b) Three-dimensional structure The Structure and Function of Transfer RNA
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• Accurate translation requires two steps: – First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl- tRNA synthetase – Second: a correct match between the tRNA anticodon and an mRNA codon • Flexible pairing at the third base of a codon is called wobble and allows some tRNAs to bind to more than one codon
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Amino acid Aminoacyl-tRNA synthetase (enzyme) ATP Adenosine P P P
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Amino acid Aminoacyl-tRNA synthetase (enzyme) ATP Adenosine P P P Adenosine P P P i P P i i
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Amino acid Aminoacyl-tRNA synthetase (enzyme) ATP Adenosine P P P Adenosine P P P i P P i i tRNA tRNA Aminoacyl-tRNA synthetase Computer model AMP Adenosine P
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Amino acid Aminoacyl-tRNA synthetase (enzyme) ATP Adenosine P P P Adenosine P P P i P P i i tRNA tRNA Aminoacyl-tRNA synthetase Computer model AMP Adenosine P Aminoacyl-tRNA (“charged tRNA”)
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Ribosomes • Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis • The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)
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Fig. 17-16b P site (P eptidyl-tRNA binding site) A site (A minoacyl- tRNA binding site) E site (E xit site) mRNA binding site Large subunit Small subunit (b) Schematic model showing binding sites Next amino acid to be added to polypeptide chain Amino end Growing polypeptide mRNA tRNA E P A E Codons (c) Schematic model with mRNA and tRNA 5 3
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• A ribosome has three binding sites for tRNA • From left-to-right these are: – The E site is the exit site, where discharged tRNAs leave the ribosome – The P site holds the tRNA that carries the
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Topic 12B - Translation S10 1pp - From Gene to Protein...

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