BIO250 Spr11-26

BIO250 Spr11-26 - BIO250 Introduction to Biochemistry March...

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March 25: Transport across membranes BIO250 Introduction to Biochemistry
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Today’s agenda Administrative issues Question to ponder Transport across membranes Channels Carriers - GLUT1 Regulating glucose transport Ever more complicated carriers The energetics of transport Na + K + ATPase Transporters work together
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Administrative Issues
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Announcements Next week’s lectures will be given by Dr. Platt I will therefore answer the top Q2P from today’s lecture via Blackboard For exam: You are responsible for Q2Ps even if we did not discuss their answers in class Reminder: no office hours next week
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Exam preparation A compilation of old exam questions is now available on Blackboard Use the Q2Ps as study aids Ask questions early
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Question to ponder
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The votes are in! 0 4 8 12 16 A B C D
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Question to ponder D-1 Figure 11-8 in Lehninger describes a classification scheme for integral membrane proteins (also shown on the next slide). Be sure to read the legend for an accurate description of these types. For the six types shown, answer the five questions on the last slide:
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Question to ponder D-2
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Question to ponder D-3 For which of these types could the transmembrane helices shown be amphipathic helices? Which of these types will never have carbohydrate modifications on their N-terminal domains? If you go just by the image, which of these proteins might show the highest diffusion rate in the plane of the membrane? Which might show the slowest diffusion rates? For those proteins that have a lipid anchor, speculate what type of lipid anchor might be represented (Note: the figure is somewhat inconsistent with what we have covered in lecture).
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Question to ponder D-2
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For which of these types could the transmembrane helices shown be amphipathic helices?
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Which of these types will never have carbohydrate modifications on their N-terminal domains?
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If you go just by the image, which of these proteins might show the highest diffusion rate in the plane of the membrane?
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Which might show the slowest diffusion rates?
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Speculate what type of lipid anchor might be represented.
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Any inconsistencies with what we have covered in class?
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Some of these answers are a little “fuzzy”, i.e. they depend on the exact assumptions you made. For an exam, questions will be more focused, requiring fewer implicit assumptions. These general, open-ended questions are good for thinking through which properties really matter.
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Transport across membranes
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A A A A A A A A A B B B B B B B B B B C C C C C C C C C Membranes define compartments
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How do molecules get from one side of the membrane to the other? Quite effective for some lipophilic molecules (e.g., steroid hormones) Simplest case: passive diffusion through the lipid bilayer
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molecules is inefficient Reason: molecules have to lose their hydration shell to pass through the bilayer. Thus activation energy is high. N
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BIO250 Spr11-26 - BIO250 Introduction to Biochemistry March...

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