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

Codon Table

Ribosome

Two subunits Mostly made

up of rRNAs and proteins

A, P and E site

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

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 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

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

Misuse of central dogma as a research strategy

Reductionist approach that inhibits novel approaches to understanding of more complex systems

Evidential proof: 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

Q & A

Coffeebreak?!