1. tRNA Structure and Function - Nov12

1. tRNA Structure and Function - Nov12 - tRNA Structure and...

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tRNA Structure and Function Chem 431 November 12 2009 Rebekah Nash
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DNA RNA Protein Nucleic Acids Nucleic Acids Amino Acids The Problem RNA Polymerase ??? Genetic Code tRNA Ribosome http://www.mcat45.com/content/dna-structure
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Searching for the Solution Figure 32-7 The adaptor hypothesis. It postulates that the genetic code is read by molecules that recognize a particular codon and  carry the corresponding amino acid. Page 1292 Francis Crick proposed: the adapter hypothesis  (1955) He observed:  14 C-labeled amino acids became  covalently bound to small RNAs during protein  translation Small RNAs (sRNA) = transfer RNA (tRNA) Called Crick’s adapters
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Searching for the Solution Holley identified the  RNA sequence of a  tRNA molecule tRNA Ala  from yeast Purified 1 gram of  tRNA Ala  from the other  19 tRNAs Invented an RNA  sequencing method Discovered that 10 of  the 76 nucleotides  were modified  Figure 32-8 Base sequence of yeast tRNA Ala  drawn in the cloverleaf form. Page 1292
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Figure 32-10 A selection of the modified nucleosides that occur in tRNAs together with their standard abbreviations. Page 1294 Modified Bases in tRNA (Part I)
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Figure 32-10  ( continued ) A selection of the modified nucleosides that occur in tRNAs together with their standard  abbreviations. Page 1294 Modified Bases in tRNA (Part II)
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Structure of tRNA Figure 32-9 Cloverleaf secondary structure of tRNA. Page 1293 1)  5’-phosphate 2)  7-bp  Acceptor Stem 1) D Arm 3 bp stem with dihydrouridine (D) base 4) Anticodon Arm 5 bp stem with triplet anticodon 5) Variable Arm 3-21 nts 6) T Arm 5 bp stem with T Ψ C; Ψ  = pseudouridine 7) CCA with 3’-OH 5 bp stem with T Ψ C; Ψ  = pseudouridine
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Structure of tRNA Alexander Rich, Sung- Ho Kim, Aaron Klug  solved the crystal  structure of yeast  tRNA Phe  (1974) Observed an L-shaped  molecule Acceptor  +  T-arm  form  single A-form RNA helix Anticodon  D-arm   form another A-form  RNA helix Figure 32-11a Structure of yeast tRNA Phe . ( a ) The base sequence drawn in  cloverleaf form.
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