L07_2008%20Membrane%20Structure%20and%20Function

L07_2008%20Membrane%20Structure%20and%20Function - Membrane...

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Unformatted text preview: Membrane Structure and Function Lecture 07, Cole Gilbert September 12, 2008 PHI TUG!!! Are YOU man enough to take on the Cornell Men’s Wrestling Team? What: TUG-O-WAR tournament, FREE food, MUSIC Where: Court/Kay/Bauer Courtyard, North Campus When: Sunday, September 21st at 1:00pm Why: Support the Hole in the Wall Camps (send kids suffering from various How to sign up: Send an e-mail to [email protected] or go to www.phitug.org or just show up diseases to summer camp) ! "#$$ "% #&' ( ' # Sponsored By Cornell Student Society for Public Health csspublichealth.org 1 . / 01 2 4& 1 5 6* 2 21 ," * 8 + 8 $ 1# $ . ; / 1 1! 9 : 1 3 3 3 7 *" + , %" % + !# " $ %& %( " ') “MEET YOUR PROFESSOR” GUEST: Dr. Cole Gilbert, Instructor, BioG 1101 Room 302AB APPEL DINING HALL 5:45 PM Meeting place: West Entrance to Appel Center at 5:45pm Monday, 15 Sep. 2008 All BioG 1101 students are expected to participate in one Explorations Program. Registration materials will be distributed in lecture today, Friday, September 12. Electronic registration will begin at 7:30 a.m. on Monday, September 15 using the course website. --|-- Programs are filled on a first-come-first served basis, so register early to ensure placement in your top choice --|-- Registration deadline is Friday, September 19 at noon. --|-Register by the deadline, attend, and evaluate your program to receive full credit. Contact Debbie Doolittle: [email protected] with your questions. Where we’re going 1. Lipids and steroids 2. Membrane models 3. Membrane proteins 4. Passive permeability 5. Active permeability Lipids: Fats & oils Fatty acids (FA): long carbon chains ending in carboxylic acid Straight chain (saturated) FAs tend to be firmer Kink due to double bond (unsaturated) tend to be oilier Stearic acid = = Oleic acid 2 2 2 Storage Lipids: Acylglycerols Phospholipids: components of membranes Heads – polar, hydrophilic Twin tails – non-polar, hydrophobic Ester Linkage (b) Fat molecule (a triacylglycerol or triglyceride) Steroids found in plants and animals 1. important components of membranes – regulate fluidity 2. used as hormones Plant sterols sitosterol cholesterol stigmasterol Sex hormones Insect sterols ecdysone progesterone Illegal sterols moulting hormone aldosterone testosterone estradiol Androl ® 3 MEMBRANE STRUCTURE 1915 Data: Membrane consists of phospholipids and proteins 1925 Data: Stable phospholipid bilayer can selfassemble 1935 Data: Membrane is more wettable than a pure phospholipid bilayer Red blood cell ghosts 1915 Davson & Danielli propose sandwich model with more hydrophilic proteins on the outside 1950s Data: Transmission electron microscopy (TEM) reveals 3 layered sandwich Problems with Davson-Danielli model Data: Cholesterol is present in membranes of eukaryotes, but not in prokaryotes Data: Plasma membrane is 7-8 nm thick, 3 layers but mitochondrial membrane is only 5-6 nm thick and looks like a row of beads, not a sandwich Data: Protein composition differs in different membranes inside Most inconsistent data: membrane proteins are not very soluble in water and have hydrophobic regions me ran mb e outside Fluid Mosaic model SJ Singer & GL Nicholson, 1972 hydrophilic region of protein Prediction: Freeze fracture, scanning electron microscopy (SEM) should reveal proteins embedded in the membrane phospholipid bilayer hydrophobic region of protein Freeze fracture replicas of membranes are studded with globular proteins Extracellular half of bilayer viewed from within (E face) The scientific way of knowing make observations eureka ! EUREKA ! form hypothesis form alternative hypothesis test predictions with experiments & new observations Cytoplasmic half of bilayer viewed from outside (P face) do new data fit predictions? no Wait for call from Stockholm draw conclusions publish yes 4 Fluidity of membrane - lipids Membrane fluidity depends upon lipid components of membrane, temperature more fluid Classes of Membrane Proteins cis unsaturated hydrocarbon tails with kinks Effect of cholesterol varies with temperature. At body temperature it stiffens by impeding flow of phospholipids At cooler temperature it makes more fluid by preventing tight packing integral (amphipathic) peripheral some are more fluid than others Why some membrane proteins are not fluid Protein aggregation Protein tethering external internal Cell-cell interactions (junctions) Membrane permeability is selective hydrated ions Movement of molecules across a membrane is driven by diffusion, a passive process Rate of movement depends upon… Temperature Concentration gradient Charge Permeability of membrane area transport protein or not Diffusion across a membrane is passive single type of molecule two types of molecule 5 Osmosis: special case of diffusion of water Movement of water into a cell causes increase in volume or increase in pressure (and vice versa) low concentration of impermeable solutes external to the cell high Sugar molecules too large to pass through the membrane Therefore, organisms try to regulate the osmotic pressure on the membrane Passive movement of molecules across the membrane with the help of transport proteins Facilitated diffusion Aquaporin: water channel Peter Agre (Nobel Prize 2003) Some molecules require active transport to be moved across a membrane Typically fueled by energy from hydrolysis of ATP (or GTP) Molecules can be moved against their concentration gradient e.g., Sodium/Potassium pump - maintains a concentration gradient for both K+ and Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ P ADP ATP P Na+ Na+ Co-Transport: active transport driven by energy from a concentration gradient K+ K+ K+ K+ K+ K+ P P Proton pump creates voltage gradient. coupled transport uses electrogenic energy to move solute against concentration gradient 6 Up next Composition of Cells 7 ...
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This note was uploaded on 10/13/2009 for the course BIO G 1101 at Cornell.

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