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mcdb100prob_2answers_08W

# mcdb100prob_2answers_08W - Name TA Session MCDB 100 Problem...

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Name______________________________ TA / Session ______________________________ MCDB 100 Problem Set #2 Jan 15,2008 Due: In class Jan 24, 2008 1. (a) How many phospholipid (PL) molecules, each occupying 0.7nm 2 of surface area, are there in a human red blood cell (RBC) surface membrane? Assume the surface area of an RBC is equivalent to a sphere of ~ 6.7 µ m. Area =S RBC = π d 2 = 3.14x (6.7x 10 3 ) 2 = 1.4 x 10 8 nm 2 N PL = S RBC / S PL = 1.4 x 10 8 nm 2 / 0.7nm 2 = 2x 10 8 molecules 1. (b) Experimental measurements gives about 4x 10 8 molecules per RBC. What does this tell you about the PL organization of the RBC? The number calculated is ½ the experimental value suggesting that the ___ RBC cell membrane is a bilayer _____________________________________ ________________________________________________________________ 2. Many integral membrane proteins are free to move in the plane of the cell membrane. (a) What is the average distance traversed by such a protein in 1 sec? Assume the diffusion coefficient s 10 -8 cm 2 /sec. Ans: <x 2 > =2Dt or x = 2Dt = 2x 10 -8 x1 = 1.4 µ m (b) How long would it take for such a protein to go once around a liver cell assumed to be a 20 µ m sphere? To simplify just compute this for a circumferential path.

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