Transcript Central Dogma of Molecular Biology

Presentation Outline
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PART I
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The Basics
DNA Replication
Transcription
PART II
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Translation
Protein Trafficking & Cell-cell communications
Criticisms & Conclusion
Translation
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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
Codon Table
Ribosome
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Two subunits
Mostly made
up of rRNAs
and proteins
A, P and E
site
tRNA the Middle Man
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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 WatsonCrick base pairing)
Is responsible for the specificity of
the codon recognition
tRNA Charging
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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
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Initiation
Recognition and specificity
Shine Dalgarno Sequence
Elongation
Termination
Recognition of STOP codons
Usage of release factors
Translation Termination
Lipid Bilayer
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
Cell Signaling
Key points:
• Quorum Sensing
• Membrane Receptors
• Protein Switches
Quorum Sensing
Autocrine signaling
Secreted signal molecule affects the same cell
 Signal is released at high signal molecule
concentration (high cell count)
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Examples:
lux operon (LuxR/LuxI) in Vibrio fischeri
las operon (LasR/LasI) in Pseudomonas aeruginosa
exp operon (ExpR/ExpI) in Erwinia carotovora
Lux Operon
Membrane Receptors
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
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Misuse of central dogma as a
research strategy
Reductionist approach that
inhibits novel approaches to
understanding of more
complex systems
Evidential proof:
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Viruses
Prions
Central dogma: Alternative thinking
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."
End of Part II
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Q&A
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Coffeebreak?!