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Presentation Outline. PART I The Basics DNA Replication Transcription. PART II Translation Protein Trafficking & Cell-cell communications Criticisms & Conclusion. Translation. Interpreting the information coded in the mRNA into proteins

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Presentation Outline

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  1. Presentation Outline • PART I • The Basics • DNA Replication • Transcription • PART II • Translation • Protein Trafficking & Cell-cell communications • Criticisms & Conclusion

  2. Translation • Interpreting the information coded in the mRNA into proteins • The nucleotides are read in triplets (set of three) called codons • Each triplet code for a specific amino acid, and sometimes more than one codon exist for an amino acid • mRNA are read by the translational machinery including ribosomes, tRNAs and rRNAs • Like transcription, it also includes initiation, elongation and termination

  3. Codon Table

  4. Ribosome • Two subunits • Mostly made up of rRNAs and proteins • A, P and E site

  5. tRNA the Middle Man • Is in a clover shaped structure • Brings the amino acids to the mRNA • Has an anticodon loop to recognise the codons in the mRNA (by Watson-Crick base pairing) • Is responsible for the specificity of the codon recognition

  6. tRNA Charging • Aminoacylation is the process of adding an aminoacyl group to a compound. • It produces tRNA molecules with their CCA 3' ends covalently linked to an amino acid • Each tRNA is aminoacylated(or charged) with a specific amino acid by an aminoacyl tRNA synthase. • There is normally a single aminoacyl tRNA synthetase for each amino acid, despite the fact that there can be more than one tRNA, and more than one anticodon, for an amino acid.

  7. Process of Translation • Initiation • Recognition and specificity • Shine Dalgarno Sequence • Elongation • Termination • Recognition of STOP codons • Usage of release factors

  8. Translation Termination

  9. Lipid Bilayer

  10. Protein Trafficking • Protein is translated but not folded • Signal sequence determines localization • Unfolded protein is transported out • Extracellular conditions allow protein folding

  11. Protein Import • Import of molecules require channels • Channels should be able to control flux of molecules

  12. Cell Signaling Key points: • Quorum Sensing • Membrane Receptors • Protein Switches

  13. Quorum Sensing • Autocrine signaling Secreted signal molecule affects the same cell • Signal is released at high signal molecule concentration (high cell count) Examples: lux operon (LuxR/LuxI) in Vibrio fischeri las operon (LasR/LasI) in Pseudomonas aeruginosa exp operon (ExpR/ExpI) in Erwinia carotovora

  14. Lux Operon

  15. Membrane Receptors

  16. Protein Switches • Protein is modified after translation • Modifications can activate or inactivate the protein • This is faster than regulating expression

  17. Two-Component Systems • Signal binds membrane receptor • Kinase domain autophosphorylates • Phosphate group transferred to regulator • Regulator is active

  18. Central dogma: Criticisms • Misuse of central dogma as a research strategy • Reductionist approach that inhibits novel approaches to understanding of more complex systems • Evidential proof: • Viruses • Prions

  19. Central dogma: Alternative thinking

  20. Conclusion As Horace Freeland Judson records in The Eighth Day of Creation: "My mind was, that a dogma was an idea for which there was no reasonable evidence. You see?!" And Crick gave a roar of delight. "I just didn't know what dogma meant. And I could just as well have called it the 'Central Hypothesis,' or — you know. Which is what I meant to say. Dogma was just a catch phrase."

  21. End of Part II • Q & A • Coffeebreak?!

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