Presentation Outline

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Presentation Outline

• PART I
• The Basics
• DNA Replication
• Transcription

• PART II
• Translation
• Protein Trafficking Cell-cell communications
• Criticisms Conclusion

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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

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Codon Table
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Ribosome

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

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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

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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.

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Process of Translation

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

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Translation Termination
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Lipid Bilayer
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Protein Trafficking

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

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Protein Import

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

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Cell Signaling

• Key points
• Quorum Sensing
• Membrane Receptors
• Protein Switches

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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

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Lux Operon
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Membrane Receptors
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Protein Switches

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

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Two-Component Systems

• Signal binds membrane receptor
• Kinase domain autophosphorylates
• Phosphate group transferred to regulator
• Regulator is active

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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

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Central dogma Alternative thinking
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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."

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End of Part II

• Q A
• Coffeebreak?!