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Translation: From RNA to Protein

Translation: From RNA to Protein. Overall Picture. Protein. Universal Code. tRNA. To translate the mRNA transcript into a protein, the codons must be read one at a time to assemble amino acids in the right sequence This occurs in the ribosome with the help of transfer RNA ( tRNA ).

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Translation: From RNA to Protein

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  1. Translation:From RNA to Protein

  2. Overall Picture • Protein

  3. Universal Code

  4. tRNA • To translate the mRNA transcript into a protein, the codons must be read one at a time to assemble amino acids in the right sequence • This occurs in the ribosomewith the help of transfer RNA (tRNA)

  5. Structure of tRNA glu A tRNA molecule bound to an amino acid is called an amino - acyl tRNA( aa-tRNA) amino acid anticodon

  6. tRNA

  7. tRNA

  8. Structure of tRNA • Folded RNA molecule with an anticodonloop • the anticodon contains a nucleotide triplet which is complementary to the mRNA codon • Each tRNA carries a particular amino acid corresponding to its anticodon

  9. Reusing tRNA

  10. How Many Codon Permutations? A 43 = 64 U ? C G

  11. Universal AND Redundant

  12. The Wobble Hypothesis • Though there are 61 codons coding for amino acids, we do not need 61 types of tRNA • The 3rd nucleotide in the anticodon is often less important than the first two(binds weakly / not specific) • The third nucleotide is in the“wobble” position

  13. The Wobble Hypothesis • UCC and UCU both code for serine

  14. The Ribosome • A ribosome is a complex of protein combined with ribosomal RNA (rRNA) • 2 subunits : small and large 3 binding sites for tRNA • P siteholds one aa - tRNAand the growing chain of amino acids • A sitereceives the tRNAwith the next amino acid to be added to the chain • E sitereleases the used tRNA back into the cytoplasm Large ribosomal subunit E P A Small ribosomal subunit

  15. Phases of Translation • Initiation • Elongation • Termination

  16. Initiation • In the cytoplasm a small portion of mRNA binds to rRNA on the small ribosomal subunit • A tRNA molecule with the start anticodon UAC (to complement the start codonAUG) binds to the mRNA - rRNAcomplex. The start tRNA carries the amino acid methionine • This complex then binds to the large ribosomal subunit

  17. C A A C G U G U G U U G U G A G U A P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S Initiation 3’ 5’ E P A tRNA 5´ 3´

  18. Initiation

  19. Elongation The cycle of elongation has 3 steps: • aa-tRNA binds to the A site. • The large ribosomal subunit catalyzes the formation of a peptide bond with the previous amino acid. At the same time the polypeptide chain is passed from the tRNA in the P site to the tRNA in the A site. Translates 5’  3’ • Translocation:The ribosome moves 3 nucleotides (one codon) along the mRNA. This releases the used tRNA at the E site and frees the A site for a new aa-tRNA to bind

  20. U U A G G U U A C G U G A G G C A U P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S Elongation E P A 5´ 3´

  21. U U A G G U U A C G U G A G G C A U P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S Elongation E P A 5´ 3´

  22. U U A G G U U A C G U G A G G C A U P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S Elongation E P A 5´ 3´

  23. U U A G G U U A C G U G A G G C A U P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S Elongation E P A 5´ 3´

  24. U G G U G C U U U A G U G A C G A A P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S Elongation Growing polypeptide chain E P A 5´ 3´

  25. Elongation

  26. Termination • There is no tRNA with the complementary anticodon for the stop codon • A protein release factor binds to the stop codon in the A site • This cleaves the polypeptide from the tRNA and breaks apart the ribosomal sub-units I love protein

  27. U G C U G U C U U A U G G C G A G A G C C A U U A C A P P P P P P P P P P P P P P P P P P P P P P P P P P P S S S S S S S S S S S S S S S S S S S S S S S S S S S Termination I’ll be back! protein E P A Release factor (protein) 3´ 5´ mRNA

  28. Termination

  29. Polysome • One mRNA can be bound simultaneously to more than one ribosome. This is a polysome!(called a polyribosome in your textbook)

  30. Electron Micrograph

  31. 3D Shape • During translation polypeptides fold into a complex3D shape • NOT DONE YET! Most newly synthesized proteins need modification in the ER and/or Golgi: Post-translational modifications: • some amino acids may be removed • polypeptide can be divided into pieces • sugar and phosphate may be added • several polypeptides can join to form quaternary structure

  32. Summary

  33. Homework Your homework this evening is to: • Write captions for the diagrams provided • Do the section review questions on p. 331 #1-8

  34. Structure of tRNA Ileu amino acid 3’ A tRNA molecule bound to an amino acid is called an amino - acyltRNA ( aa-tRNA) 5’ anticodon

  35. Polysome

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