NE102 Lecture Notes 2

1900 q3 how are vesicles targeted to the correct

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19:00 Q3: How are vesicles targeted to the correct membrane? Cell membranes are associated with specific Rab proteins, which recruit tethering  proteins.  Protein-protein interactions between tethering proteins result in vesicle docking at its  target membrane.  Q4: Once docked at a target membrane, how do the membranes fuse? Driven by transmembrane proteins called SNAREs Two types: a.i.1. v-SNAREs – located on vesicle (i.e., vesicular-SNAREs) a.i.2. t-SNAREs – located on the target membrane (i.e., target- SNAREs The SNAREs are brought together by the Rabs & tethering proteins.  SNAREs warp around each other to form “colied-coils”.  Destabilizes the membrane & spontaneously fuses Vesicular trafficking between the Golgi & plasma membrane is bi-directional. Endocytic pathway  proceeds through early and late endosomes. Endosomes function largely as sorting compartments Called  “receptor-mediated endocytosis” Internalized cargo is transported to lysosomes for degradation. Lysosomes  are specialized compartments for degradation of various substances.  Contain digestive types of substances Internalized receptors are transported back to the cell surface via the recycling pathway.  Many cell surface proteins undergo complex trafficking between cell surface &  endosomes E.g., amyloid precursor protein (APP) Q: How is cargo recognized for import? Transmembrane receptors FINAL Q: How do cells transport vesicles to their target membrane/destination? Story of “tracks” and “trains” OVERRIDING QUESTION: What is the “cytoskeleton” and what role(s) does it play?
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Cytoskeleton and Motor Proteins 19:00 Three classes:
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Cytoskeleton and Motor Proteins 19:00 Actin filaments Intermediate filaments Microtubules In common: All three classes are long filaments built from the assembly of protein  monomers.  Differ in: Protein monomers Assembly & regulation Roles in the cell All three provide cells with structure Challenge for cells: Phospholipid bilayers naturally assume spherical structures… …yet, cell membranes take on much more complex structures Q: HOW? The cytoskeleton is built into a rigid scaffolding that provides structure.  MIRCOTUBULES (MTs) Polymers of tubulin
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Cytoskeleton and Motor Proteins 19:00 Dimers of two distinct tubulins (a- & b-tubulin) = MT building blocks B-tubulin/a-tubulin can be assembled in different ways: Protofilaments 13 protofilaments are assembled in paralleled around a hallow core forming a  microtubule Polar filaments due to head-to-tail assembly of tubulin dimers.
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