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
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
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
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
Initiation Recognition and specificity Shine Dalgarno Sequence Elongation Termination Recognition of STOP codons Usage of release factors
Protein Trafficking
• Protein is translated but not folded
• Signal sequence determines localization
• Unfolded protein is transported out
• Extracellular conditions allow protein folding
Protein Import
• Import of molecules require channels
• Channels should be able to control flux of molecules
Quorum Sensing
Autocrine signalingSecreted signal molecule affects the same cell Signal is released at high signal molecule
concentration (high cell count)
Examples:lux operon (LuxR/LuxI) in Vibrio fischerilas operon (LasR/LasI) in Pseudomonas aeruginosaexp operon (ExpR/ExpI) in Erwinia carotovora
Protein Switches
• Protein is modified after translation
• Modifications can activate or inactivate the protein
• This is faster than regulating expression
Two-Component Systems
• Signal binds membrane receptor
• Kinase domain autophosphorylates
• Phosphate group transferred to regulator
• Regulator is active
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
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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