20 - Wednesday, October 12, 2011 Lecture 20 Announcements:...

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Wednesday, October 12, 2011 Lecture 20 Announcements: 1. Reading & problem assignments for this week DIFFER from what is shown in the LG, but instead are as shown for 10/14 & 10/19: text pp. 343-363 and 371- 389 and text problems Ch.10 #7,16 and Ch.11 #4,15 and LG problems 32-34. 2. Reminder: no quiz next Wednesday, 10/19. 3. PyMOL #6, chymotrypsin, will appear on the prelim, but no other PyMOL. 4. Friday 10/14 2:55 - 4PM in Comstock B108: “How to study for this course”. No discussion of material on the 10/20 prelim, but prof will outline how to study effectively, and answer questions about the exam. 5. Rooms for the 10/20 exam: Last names A - M in Rockefeller Schwartz Auditorium; N - Z in Rockefeller 203 (“Auditorium B”). Lecture from Friday 10/7/10 Regulation of enzyme action Control of enzyme activity. Example of aspartate carbamoyltransferase = ATCase. Control of chymotrypsinogen activation to chymotrypsin Intro to biomembranes Today's lecture: The unsaturated hydrocarbon chains , those with at least one double bond, are very important for keeping the bilayer somewhat fluid . This is because saturated, unbranched hydrocarbon chains can pack together tightly, forming a solid bilayer. This tight packing would not allow movement of proteins within the membrane. Unsaturated lipids increase the fluidity of the membrane. For almost all cases, it is not known why some lipid acyl chains are multiply unsaturated. In addition, it is not known why there are different chain lengths. In the middle of page 152 is stearate, abbreviated as 18:0, an example of a saturated lipid chain. The structure is straight, as opposed to that of oleate, abbreviated 18:1, which has one double bond that forms a kink in the molecule. Now imagine how well many stearate molecules could pack closely together, as opposed to how poorly oleate molecules would pack with each other and with other stearate molecules. (Note: learn the “ system” for describing the location of double bonds, text pp 343-344). Nearly a third to half of all the lipid in mammalian plasma membranes is cholesterol! We do know that cholesterol decreases the permeability of the
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bilayer. Also, cholesterol induces the liquid-ordered phase. But beyond these simple facts, we do not yet know its full role. Cholesterol is almost entirely hydrocarbon, with just one little OH group, and this lack of polarity might play a role. At the top of p. 153 is a drawing of the general structure of glycerophospholipids . These are one of the main types of biomembrane lipids, and most of these spontaneously form a bilayer upon mixing with water. A glycerophospholipid has three main parts: . A polar/charged head group that is attached to a phosphate group (the head group is represented by an X in the drawing on p. 153). There are about 10 types of head groups commonly found in biomembranes of mammals. Several of these polar head groups are drawn in the table. Considering plants and bacteria too, there are many many more polar head groups than shown in this table.
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This note was uploaded on 01/01/2012 for the course BIOMG 3310 taught by Professor Feigenson during the Fall '11 term at Cornell University (Engineering School).

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20 - Wednesday, October 12, 2011 Lecture 20 Announcements:...

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