1. Translation: From RNA to Protein

2. Overall Picture Protein Processed mRNA leaves the nucleus mRNA mRNA binds to ribosome Ribosome tRNA delivers amino acids tRNA

3. 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)

4. Structure of tRNA Folded RNA molecule with an anticodon loop –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 3’3’ 5’5’ amino acid anticodon Ileu A tRNA molecule bound to an amino acid is called an amino - acyl tRNA ( aa-tRNA)

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 site holds one aa - tRNA and the growing chain of amino acids A site receives the tRNA with the next aa to be added to the chain E site releases the tRNA back into the cytoplasm EPA Small ribosomal subunit Large ribosomal subunit

9. Phases of Translation Three phases 1.Initiation 2.Elongation 3.Termination

10. Initiation 1. In the cytoplasm the ribosome attaches onto the mRNA at the 5’ cap. 2. 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 3. This complex then binds to the large ribosomal subunit

11. Initiation EPA 5´3´ S G PS G PS U PS U PS A PS G PS A PS U PS C PS G PS G PS U PS A PS U PS G PS A PS U PS C P 3’3’ 5’5’ tRNA

12. Initiation

13. Elongation The cycle of elongation has 3 steps: 1. aa-tRNA binds to the A site (aminoacyl site ). 2. 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 3. 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. Elongation EPA 5´3´ S G PS G PS U PS U PS A PS G PS A PS U PS C PS G PS G PS U PS A PS U PS G PS A PS U PS C P

15. Elongation EPA 5´3´ S G PS G PS U PS U PS A PS G PS A PS U PS C PS G PS G PS U PS A PS U PS G PS A PS U PS C P

16. Elongation EPA 5´3´ S G PS G PS U PS U PS A PS G PS A PS U PS C PS G PS G PS U PS A PS U PS G PS A PS U PS C P

17. Elongation EPA 5´3´ S G PS G PS U PS U PS A PS G PS A PS U PS C PS G PS G PS U PS A PS U PS G PS A PS U PS C P

18. Elongation EPA 5´3´ S G PS G PS U PS U PS A PS G PS A PS U PS C PS G PS G PS U PS A PS U PS G PS A PS U PS C P Growing polypeptide chain

19. Elongation

20. Termination 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 tRNA and breaks apart the ribosomal sub-units I love protein

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

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. EPA 5´3´ S G PS G PS U PS C PS C PS G PS A PS U PS C PS G PS G PS U PS C PS C PS G PS A PS U PS C P