Endomembrane System, Membrane Trafficking Pathways, Budding & Fission, Vesicle Coats & Assembly

4 Pages

Biochemistry & Molecular Bio.
Course Code
David Gross

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March 31 • Membrane topology o lumen of endomembrane system topologically identical to outside of cell • Endomembrane system o complex network of membrane structures responsible for membrane synthesis, membrane turnover & secretion o trafficking btwn compartments of endomembrane system bidirectional in most cases  necessary to maintain proper distribution of membrane within cell o vesicular trafficking within endomembrane system can be constitutive or regulated depending on cargo involved • 2 types of membrane trafficking pathways o endocytosis (fission) o exocytosis (fusion) o bulk transport of many different proteins o proteins generally folded into 3D structure o transport occurs via vesicular transport • Vesicular transport o selectively moves cargo from 1 emdomembrane compartment to another o there is donor & target membrane o the process includes budding & fusion  budding is process by which specific cargo packaged into site on donor membrane & membrane encapsulates cargo to form membrane bud  fusion results in delivery of cargo from donor to target membrane • Budding is facilitated by vesicle coats o cargo receptors are integral membrane proteins, bind cargo in lumen  binding of cargo to receptor mediated by specific targeting signals within cargo  binding triggers association of adapters & specific lipids, recruit coat proteins o coat proteins recruited to specific sites on membrane via interaction w/ cargo receptors in cytoplasm  interact w/ adapters attached to receptors  begins deformation of membrane & initiates bud formation o bud formation begins o membrane fission gives rise to vesicle  once bud formed specific fission proteins form around neck & pinch off bud to release the vesicle into cytoplasm o in cytoplasm, coat & adaptors dissociate from vesicle, unfavorable rxn • Specific coats for each trafficking pathway o specific coated vesicles are involved in specific anterograde & retrograde transport pathways  anterograde (forward trafficking) delivers cargo outward • example is COPII  retrograde (reverse trafficking) delivers cargo from outside to the cell & returns components to donor membranes
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