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bis_104_sample_exam_ii_key_08 - Page 1 Name The diagram...

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Page 1 Name _____________________________ The diagram depicts a model for arteriogenesis in the embryonic limb skin. Peripheral sensory nerves (PSNs) 1 and/or associated Schwann cells 2 synthesize and secrete VEGF protein 3 . VEGF acts on undifferentiated (PECAM-1-positive; ephrinB2-negative) endothelial cells (ECs) 4 , some of which have transmembrane receptors for VEGF 5 . In response to binding VEGF, approx. 60% of the ECs begin to express ephrinB2 6 as they differentiate into arteries 7 . As the arterial vessels mature, smooth muscle cells (SMCs) 8 begin to associate with the vessel wall. You hypothesize that VEGF receptors in undifferentiated ECs are randomly distributed in the PM and are relatively free to move laterally in the membrane. However, once they bind VEGF, the receptors tend to cluster into discrete islands and lose their lateral mobility. 1. Describe two different cellular mechanisms that could cause the loss of mobility in these receptor/ligand complexes. (4) a) Once the ligand binds to the receptor, the cytoplasmic domain of the receptor could undergo a conformational change and link to cytoplasmic structural proteins, such as components of the cytoskeleton (microtubules; microfilaments). This linkage with cytoplasmic structures could restrict lateral mobility of the receptor / ligand complex. b) Binding of the ligand could induce the receptors to migrate into pre-existing lipid rafts and complex with proteins in the raft. These protein aggregates would be less mobile than individual smaller sized proteins. c) Binding of the ligand could cause adjacent receptors to dimerize or even aggregate into multi-receptor complexes that would have diminished lateral mobility because of their bulk. d) Less likely, but also a possibility, is that ligand-bound receptors might then link up more intimately with extra-cellular matrix components (glycoproteins, matrix adhesion molecules, etc) thus immobilizing the receptors.
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Page 3 Name ______________________________ 3. In order to characterize the plasma membrane proteins in the undifferentiated ECs, a pure (enriched) population of viable ECs was obtained. Name the technique used to obtain a pure population of viable cells. Fluorescence Activated Cell Sorting (FACS)____________________________(2) Plasma membranes from the pure ECs were subjected to SDS-PAGE following various treatments of the live cells. What conclusions can be drawn from the experimental results presented below? (8) Pre-treatment of cells analysis of PAGE gel results a. none
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