exam-answers_2003 - MCB110 FINAL May 19, 2003 . Your name...

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MCB110 FINAL May 19, 2003 . Your name and student ID QUESTION POINTS 1 (20 points) 2 (30 points) 3 (35 points) 4 (20 points) 5 (20 points) 6 (25 points) 7 (15 points) 8 (10 points) 9 (15 points) 10 (25 points) 11 (15 points) 12 (25 points) 13 (25 points) 14 (30 points) 15 (20 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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Student Name and ID # 1(a) - Which of the following organisms do you think must have the highest proportion of unsaturated fatty acids in their membranes and why (10 p): (a) Antarctic fish (b) Cactus (c) Bacteria from thermal hot springs (d) Humans Antarctic fish (a), as they will need the unsaturated fatty acid chains in order to lower the critical temperature for the transition from a liquid crystal (fluid) to a gel phase (rigid) below the temperatures in the Antarctic. 1(b) - Describe the differences in self-association of lipids in monolayers, micelles and liposomes (10p). In monolayers the hydrophilic lipid heads face the water at the air-water interface, with the fatty acid chains facing the air. In micelles the lipid tails face each other in the inside of a small sphere, with the hydrophilic heads facing the water on the outside. In liposomes the lipids form a bilayer and give rise to a large sphere with an aqueous core. 2(a) - What are the most common arrangements of secondary structure elements in the lipid- interacting section of integral membrane proteins? Could you predict them having knowledge of the protein sequence but lacking direct structural data? (10 p) Transmembrane regions in integral membrane proteins are an alpha helix (single pass) or alpha helical bundle (several passes) and beta barrels. Transmembrane helices can be predicted from hydropathy plots by identifying hydrophobic regions in the sequence spanning about 20-30 a.a. This method will not be able to predict beta barrels. 2(b) – During purification of membrane proteins, what different methods would you use to separate from the membrane integral membrane proteins, peripheral proteins and lipid-anchored proteins (10 p). Integral membrane proteins will have to be solubilized using non-ionic detergents; peripheral proteins can be release from the membrane with high salt or alkaline pH; phospholipases (or enzyme that break covalent bonds between the protein and its linked hydrocarbon chain) will be needed to release the lipid-anchored proteins.
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Student Name and ID # 2(c ) - You are using FRAP to study an integral membrane protein resident in the ER. What would be your conclusion if you see a fast rate or recovery? Would you expect a faster or slower recovery if you lower the temperature of your cells? (10 p) The recovery after photobleaching means that the protein is free to diffuse within the ER membrane. Lower temperature will reduce the fluidity of lipids and thus the diffusion rate of
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exam-answers_2003 - MCB110 FINAL May 19, 2003 . Your name...

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