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Translation: From RNA to Protein

Translation: From RNA to Protein. Overall Picture. Protein. 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 ). Structure of 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. 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)

  4. Structure of tRNA • Folded RNA molecule with an anticodonloop • anticodon contains nucleotide triplet which is complementary to mRNA codon; each codon codes for a specific amino acid • each tRNA carries a particular amino acid corresponding to its anticodon

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

  6. Activation Enzymes • Ensure that the correct A.A. is attached to the tRNA

  7. Wobble • The cell only makes 30 - 45 tRNA molecules of the possible 64 because of the redundancy in the genetic code • “wobble” phenomenon The 3rd nucleotide in the anticodon is less important(binds weakly ; not specific)

  8. The Ribosome • A ribosome is a cluster of protein combined with ribosomal RNA (rRNA) • 2 subunits : small (40s) and large (60s) 3 binding sites for tRNA • P siteholds one aa - tRNA and the growing chain of amino acids • A sitereceives the tRNA with the next aa to be added to the chain • E sitereleases the tRNA back into the cytoplasm Large ribosomal subunit E P A Small ribosomal subunit

  9. Phases of Translation • Three phases • Initiation • Elongation • Termination

  10. Initiation • In the cytoplasm the ribosome attaches onto the mRNA at the 5’ cap. • A tRNA molecule with the start anticodon UAC (to complement the start codon AUG) binds to the mRNA - rRNA complex. The start tRNA carries the amino acid methionine • This complex then binds to the large ribosomal subunit

  11. 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´

  12. Initiation

  13. Elongation The cycle of elongation has 3 steps: • aa-tRNA binds to the A site (aminoacyl 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 (peptide site)to the tRNA in the A site. The ribosome moves along mRNA in 5’ 3’*ie. Translates in 5’ 3’ direction • Translocation:The ribosome moves 3 nucleotides (one codon) along the mRNA. This releases the used tRNA at the E site (exit site) and frees the A site for a new aa-tRNA to bind

  14. 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´

  15. 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´

  16. 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´

  17. 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´

  18. 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´

  19. Elongation

  20. Termination I love protein • There is no tRNA with the complementary anticodon for the stop codon (UGA, UAG, UAA) • A protein release factor binds to the A site • This cleaves the polypeptide from the tRNAand breaks apart the ribosomal sub-units

  21. 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

  22. Termination

  23. 3D Shape • During translation polypeptides fold into a 3D shape • NOT DONE YET! Most newly synthesized proteins need modification in the ER and/or Golgi: After translation: • 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

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

  25. Polysome

  26. Summary

  27. Homework Modelling Translation Activity – answer the questions provided.

  28. U G C U G G G A C A C G C U U G C C 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 E P A 5´ 3´

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