20 - Wednesday Lecture 20 Announcements 1 Reading problem...

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Wednesday, October 13, 2010 Lecture 20 Announcements: 1. Reading & problem assignments for this week DIFFER from what is shown in the LG, but instead are as shown for 10/18 & 10/20: text pp. 343-363 and 371- 389 and text problems Ch.10 #7,16 and Ch.11 #4,16 and LG problems 32-34. 2. Reminder: no quiz next Wednesday, 10/20. 3. PyMOL #6, chymotrypsin, will appear on the prelim, but no other PyMOL. 4. Friday 10/15 2:55 - 4PM in Comstock B108: “How to study for this course”. No discussion of material on the 10/21 prelim, but prof will outline how to study effectively, and answer questions about the exam. 5. Rooms for the 10/21 exam: Last names A - T in Baker 200; U - Z in Baker 219. 6. Review session on Monday 10/18 will focus on course material up to LG page 106; the review on Tuesday 10/19 will focus on LG material pp 107 - 148. Lecture from Friday 10/8/10 Regulation of enzyme action A. Control of protein degradation B. Control of enzyme activity. Example of aspartate carbamoyltransferase = ATCase. C. Control of chymotrypsinogen activation to chymotrypsin Today's lecture: Page 149 Now we begin discussion of a new topic in this course: biomembranes The lipid bilayer is as ancient as the first cell. It is required in order to separate the cell from the environment. Cell membranes range from 30 - 70% protein and 70 - 30% lipid, and about 5% carbohydrate. The carbohydrate is always attached to either lipid or protein (never “free” carbohydrate). The word “lipid” is from the Greek word meaning "fat". In biomembranes, most lipids are amphiphilic , which means "both-love", since amphiphiles favor both water and oil. Many amphiphile lipids from biomembranes spontaneously form a lipid bilayer when added to water: Bilayer formation is a property of the amphiphilic lipids , not the proteins of the membranes. The lipid bilayer is NOT permeable (on a timescale of hours, or even far longer for larger or charged molecules) to (ions; large molecules, medium-sized but highly polar molecules) : . saccharides
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. amino acids and proteins . nucleic acids . ions The lipid bilayer is permeable to (small and uncharged molecules): H 2 O, O 2 , N 2 , CO 2 , ethanol, uncharged sterols, uncharged fatty acids p. 150 For simple lipid mixtures , we know some facts that are important for real biomembranes. Here we use the term “phase” to describe the state of the 2- dimensional matter of the bilayer mixture: 1. The phase can be liquid: acyl chains wiggling a lot; whole molecules "turning
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20 - Wednesday Lecture 20 Announcements 1 Reading problem...

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