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Chapter 14

Chapter 14. Translation. 16 and 18 October, 2006. Overview. Translation uses the nucleotide sequence of mRNA to specify protein sequence. Each ORF specifies a polypeptide.

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Chapter 14

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  1. Chapter 14 Translation 16 and 18 October, 2006

  2. Overview • Translation uses the nucleotide sequence of mRNA to specify protein sequence. • Each ORF specifies a polypeptide. • Ribosome components and / or tRNAs recognize structures and sequences near the 5’ end of the transcript to identify the correct start codon. • tRNAs are highly modified short RNAs that are the adaptors between codons and amino acids. • Amino acyl tRNA synthetases recognize structural features of tRNAs and charge only the correct tRNA with the correct amino acid. • The large and small ribosomal subunits are extremely complex ribonucleoprotein structures that dissociate and reassociate in each round of translation. • Peptide synthesis is catalyzed by a ribozyme, and proceeds in the N-to-C terminal direction. • The ribosome uses three tRNA binding sites: A, P, and E. • tRNAs are delivered to the ribosome by EF-Tu. • EF-G GTP hydrolysis along with peptide bond formation drive ribosomal translocation. • Translation termination involves release factors and GTP hydrolysis. • Translation-dependent RNA stability assures the degradation of damaged messages.

  3. Three possible open reading frames.

  4. Shine-Dalgarno and Kozak Sequences

  5. Kozak: Identification of Consensus

  6. Kozak: Correct context makes a better barrier to downstream initiation.

  7. tRNA Structures

  8. Two-step charging of tRNA

  9. Two-step charging of tRNA

  10. tRNA Structural Elements Recognized by Aminoacyl-tRNA Synthetase

  11. Synthetase-tRNA cocrystal

  12. The Problem Solved by Editing Pockets

  13. The ribosome cannot distinguish incorrectly charged tRNAs

  14. There are twenty-one amino acids.

  15. Prokaryotic transcription and translation are linked.

  16. Composition of Ribosomes

  17. Translation Overview

  18. The Peptidyl Transferase Reaction

  19. The Ribosome

  20. Ribosome - tRNA interactions

  21. tRNA Interactions Within the Ribosome

  22. Ribosome Channels

  23. Initiation in Prokaryotes

  24. Initiation in Prokaryotes

  25. Initiation in Prokaryotes

  26. Initiation in Eukaryotes

  27. Start Codon Identification

  28. Interactions between PABP and eIF4F circularize the transcript.

  29. uORFs

  30. IRES

  31. Aminoacyl-tRNAs bind to the ribosome in a complex with EF-Tu. Ef-Tu release requires correct base pairing.

  32. The ribosome also uses minor-groove interactions between the 16S rRNA and the codon-anticodon to drive correct base pairing

  33. Accommodation (rotation) of the tRNA strains the codon-anticodon interaction causing incorrectly paired tRNAs to dissociate.

  34. Peptidyl Transferase Ribozyme

  35. Peptide bond formation and EF-G GTP hydrolysis drive translocation.

  36. EF-G is a structural homolog of EF-Tu-tRNA

  37. GTP hydrolysis drives conformational change.

  38. Peptide anticodons allow release factors to recognize the stop codon.

  39. GGQ on the RF-I stimulates peptidyl transfer to water.

  40. RRF and EF-G stimulate dissociation of the terminated ribosome.

  41. tmRNA and SsrA rescue stalled complexes

  42. Normal translation displaces exon-junction complexes.

  43. Nonsense-mediated decay is caused by undisplaced exon-junction complexes.

  44. In eukaryotes, abnormal termination causes message degradation.

  45. Title

  46. Title

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