Biochem 227_exam 1_ grading key

Biochem 227_exam 1_ grading key - Biochem 227 Exam 1 Dr...

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Biochem 227 Exam 1 Dr. Hellinga / Dr. Kuehn  DO NOT BEGIN UNTIL YOU HAVE BEEN  INSTRUCTED TO DO SO.  Please write your full name and student number at the bottom of this  cover page. Please initial the bottom right of each subsequent page. There are 6 questions, answer 5 of the 6.  Place an X over the question you are not  answering. Restrict your answers to the  boxes provided. Do not write in this box, for grading  purposes Question 1 ____/ 20 Question 2 ____/ 20 Question 3 ____/ 20 Question 4 ____/ 20            1  /  7  Initials_________
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Question 5 ____/ 20 Question 6 ____/ 20 STUDENT NAME_________________            2  /  7  Initials_________
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1) (20 points total) LIPIDS AND MEMBRANES a) ( 11 pnts) Draw a schematic of a glycerophospholipid showing all  its components,  where one fatty acid is 20:3 ( Δ 9,12) .  Circle the polar  region.  Draw the general structure of cholesterol next to as it might appear  in a leaflet of a cell membrane. b) (3 pnts) Explain why triglycerides do not form bilayer membranes. c) (2 pnts) While purifying membranes from your favorite cells, you  notice that Your Favorite Protein (YFP) is present in the membrane  fraction. You find that you can elute it away from membranes with salt or  detergent, but not with glucose.  What can you conclude about how YFP             3  /  7  Initials_________ glycerophospholid required  components:  glycerol,  phosphate, , appropriate X group,  FA1, FA2, circled polar region, two  double bonds between carbons 9- 10 and 12-13 Cholesterol required-  OH head,  correct orientation (OH is on the  same side as the  glycerolphospholipid) head, , 4  ring system (3-6 + 1-5), alkyl chain  Reason 1) lack of polar head group  Reason 2) 3 chains would be too wide or other steric considerations (for planar  membrane 2 chains are best) the protein may be either peripheral or integral, but credit was only given if you  mentioned either is possible. 
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d) (4 pnts) What components are in biological membranes and why  do they remain asymmetric over time?            4  /  7  Initials_________ Components:  proteins, lipids (or phospholipids and sterols), and carbs Remain asymmetric because  (uncatalyzed) flip-flop is REALLY slow.
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