exam-answers_2002 - MCB110 FINAL May 20, 2002 . Your name...

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MCB110 FINAL May 20, 2002 . Your name and student ID QUESTION POINTS 1 (20 points) 2 (15 points) 3 (10 points) 4 (40 points) 5 (10 points) 6 (15 points) 7 (10 points) 8 (25 points) 9 (10 points) 10 (15 points) 11 (10 points) 12 (10 points) 13 (10 points) 14 (25 points) 15 (25 points) 16 (50 points) TOTAL (300 points) WARNING: Your exam will be taken apart and each question graded separately. Therefore, if you do not put your name and ID# on every page or if you write an answer for one question on the backside of a page for a different question you are in danger of irreversibly LOSING POINTS!
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1.a – A bacterial colony is shifted from 25 to 37 C. How do you expect this will affect the ˚ activity of membrane desaturases? (5 p.) As the temperature goes up there will be less need of unsaturated bonds to maintain the membrane fluidity, so the activity of desaturases will go down. 1.b – Why are glycosylated lipids less likely to flip-flop than other lipids (5 p.) Glycosylated lipids will have an oligosaccharide chain, made of large, polar sugar molecules. It will be very energetically unfavorable for this oligosaccharide chain to go through the hydrophobic core of the lipid bilayer 1.c – Give an example of an application of liposomes in the study of ion channels, and one of their application in medicine (10 p.) Liposomes are used with inserted channels in patch clamping experiments. In medicine they can be used for drug delivery, especially when the drug is hydrophobic or crystalline.
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2. a – On the basis of the hydropathy plots on the right, predict which of the three proteins will be an integral membrane protein and why (5 p.) Only protein in c) is likely to have 4 helical transmembrane regions, three N-terminal and one C-terminal. 2.b – State a type of transmembrane domain/secondary structure that would not be predicted by this method and explain why. (5 p.) Integral membrane proteins made of beta sheets forming a barrel (like porins) will not be detected by this method, which is based on finding hydrophobic patches of about 20 a.a. corresponding to the length of an alpha helix across the hydrophobic part of the lipid bilayer. In beta barrels the hydrophobic and hydrophilic a.a. alternate. 2.c – Indicate two reasons why integral membrane proteins are difficult to purify and to characterize biochemically. (5 p.) They are generally very rare (just localize to the 2-D space of the membrane), and they have to be solubilized. 3 extra points if they indicate that heterologous overexpression of membrane proteins is difficult. 3. – What is the free energy cost of pumping Ca2 + out of the cell when the cytosolic
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concentration is 0.1 μM, the concentration outside is 1 mM, and the membrane potential is –70 mV? (2.3RT room = 1.4 kcal/mol; F = 23.06 kcal/mol.V; log 10 (1)=0; log 10 (10)=1; log 10 (100)=2, etc) (10 p.) G = 2.3 RT log 10 C o [ ] C i [ ] + zF D E = 1.4 log 10 (10 4 ) + (2) (23.06)(0.07) = = 5.6 + 3.2 = 8.8 kcal/mol 4.a – The K + and Na
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exam-answers_2002 - MCB110 FINAL May 20, 2002 . Your name...

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