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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
Presentation Outline
  • PART I
    • The Basics
    • DNA Replication
    • Transcription
    • Translation
    • Protein Trafficking & Cell-cell communications
    • Criticisms & Conclusion
  • 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
  • Two subunits
  • Mostly made up of rRNAs and proteins
  • A, P and E site
trna the middle man
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
trna charging
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.
process of translation
Process of Translation
  • Initiation
  • Recognition and specificity
  • Shine Dalgarno Sequence
  • Elongation
  • Termination
  • Recognition of STOP codons
  • Usage of release factors
protein trafficking
Protein Trafficking
  • Protein is translated but not folded
  • Signal sequence determines localization
  • Unfolded protein is transported out
  • Extracellular conditions allow protein folding
protein import
Protein Import
  • Import of molecules require channels
  • Channels should be able to control flux of molecules
cell signaling
Cell Signaling

Key points:

  • Quorum Sensing
  • Membrane Receptors
  • Protein Switches
quorum sensing
Quorum Sensing
  • Autocrine signaling

Secreted signal molecule affects the same cell

  • Signal is released at high signal molecule concentration (high cell count)


lux operon (LuxR/LuxI) in Vibrio fischeri

las operon (LasR/LasI) in Pseudomonas aeruginosa

exp operon (ExpR/ExpI) in Erwinia carotovora

protein switches
Protein Switches
  • Protein is modified after translation
  • Modifications can activate or inactivate the protein
  • This is faster than regulating expression
two component systems
Two-Component Systems
  • Signal binds membrane receptor
  • Kinase domain autophosphorylates
  • Phosphate group transferred to regulator
  • Regulator is active
central dogma criticisms
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

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."

end of part ii
End of Part II
  • Q & A
  • Coffeebreak?!