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Lesson 3: Translation

Lesson 3: Translation. From RNA to protein: translation. The genetic code. Three possible “reading frames”. THE ABC FOR THE DNA. Insertion ( X ) or Deletion (B). THE A X B CFO RTH EDN A. THE ACF ORT HED NA. Ribosomes in the cytoplasm of a eukaryotic cell.

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Lesson 3: Translation

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  1. Lesson 3: Translation

  2. From RNA to protein: translation The genetic code Three possible “reading frames” THE ABC FOR THE DNA Insertion (X) or Deletion (B) THE AXB CFO RTH EDN A THE ACF ORT HED NA

  3. Ribosomes in the cytoplasm of a eukaryotic cell

  4. Composition of eukaryotic ribosomes

  5. RNA-binding sites in the ribosome • Each ribosome has: • a binding site for mRNA • three binding sites for tRNA • A-site: aminoacyl-tRNA • P-site: peptidyl-tRNA • E-site: exit

  6. tRNA molecules: matching amino acids to codons in mRNA

  7. Translation of the genetic code: two adaptors that act one after another

  8. mRNA translation mechanism Step1: An aminoacyl-tRNA molecule binds to the A-site on the ribosome Step2: A new peptide bond is formed Step3: The small subunit moves a distance of three nucleotides along the mRNA chain ejecting the spent tRNA molecule Step4: The next aminoacyl-tRNA molecule binds to the A-site on the ribosome Step5: . . .

  9. The initiation phase of protein synthesis in eukaryotes • Initiation complex (small ribosomal subunit + initiation factors) • binds DNA and searches for start codon • Large ribosomal subunit adds to the complex • Translation starts • . . .

  10. Prokaryotic vs eukaryotic mRNA molecules

  11. Structure of a typical prokaryotic mRNA molecule

  12. 5´ end capping of eukaryotic mRNA molecules

  13. The final phase of protein synthesis • binding of release factor to a stop codon terminates translation • the completed polypeptide is released • the ribosome dissociates into its two separate subunits

  14. Polyribosomes: several ribosomes can simultaneously translate the same mRNA molecule

  15. Proteasomes: degradation of “unwanted” proteins in eukaryotic cells

  16. The production of a protein by a eukaryotic cell Many levels of regulation/variation

  17. Protein import by membrane-bounded organelles ATP !!!

  18. The role of signal sequences in protein sorting • proteins destined for the ER: N-terminal signal sequence that directs them • proteins destined to remain in the cytosol: no signal sequence

  19. Free and membrane-bound ribosomes

  20. ER signal sequence and SRP: directing ribosomes to the ER membrane

  21. Translocation of a soluble protein across the ER membrane

  22. Integration of a transmembrane protein into the ER membrane

  23. Integration of a double-pass transmembrane protein into the ER membrane

  24. Vesicular traffic

  25. Clathrin-coated pits and vesicles

  26. Selective transport: mediated by clathrin-coated vesicles

  27. Model of transport vesicle docking

  28. Transport vesicle fusion

  29. Protein glycosylation in the ER

  30. The Golgi apparatus

  31. Exocytosis: the regulated and constitutive pathways

  32. Exocytosis of secretory vesicles

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