bis_104_midterm_exam_i_key2_fall_07 - Page 4

bis_104_midterm_exam_i_key2_fall_07 - Page 4 - e) What role...

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PART II Page 3 Name ____________________________________ Fig 1 is an epithelial cell from normal human breast tissue. Fig. 2 is a cancerous epithelial cell taken from a breast tumor. Fig. 3 is a diagram of a fragment of the plasma membrane from the cancer cell. The diagrams show an oversimplified version of the cell, in which the plasma membrane contains only one type of protein, the growth factor receptor protein erbB2. 9. Using the plasma membrane fragment (fig.3), sketch in and label: (4) a) An external peripheral protein b) A lipid-anchored protein associated with the inner leaflet of the lipid bilayer c) Where molecules of cholesterol would be positioned in the membrane d) The erbB2 receptor protein if it is a single pass integral protein with both external and internal domains
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Unformatted text preview: e) What role does cholesterol play in regulating plasma membrane fluidity? (2) At physiological temperatures, cholesterol usually contributes to membrane stability and viscosity. But, it also acts as a buffer against abrupt transition changes between sol and gel states. Cholesterol helps to maintain optimal functional fluidity as environmental parameters change. f) What additional information about the erbB2 protein shown in fig. 2 could be obtained by subjecting the cells to freeze-fracture followed by scanning electron microscopy (SEM)? (2) Freeze-fracture / SEM would reveal the surface topography of the inner faces of both inner and outer bilayer leaflets. It would show the presence, size, and relative distribution of integral membrane proteins. Demo...
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