1. Membranes Or, How to Keep Your Insides Separated from the Outside

2. You’re building a fence around a daycare center. What do you want this fence to be able to do?

3. Think about your answers for the previous slide. How does this compare with what a cell needs from its fence?

4. Building materials Lots of molecules like to be surrounded by water. Not useful – your building materials would keep floating away from each other.

5. A better choice What about molecules that don’t like to be surrounded by water? How will they behave? = hydrophobic molecule

6. Meet the Lipids!

7. Lipid Water

8. How will these lipids arrange themselves?

9. Lipids bunch together and line up very nicely when put into water. So is this what the cell membrane looks like?

10. Model: cell membranes are made up of a single layer of lipids Prediction – if the surface area of a round cell is 150 micrometers 2 (  m 2 ) = 150  m 2 then when the cell is “unwrapped,” there should be 150  m 2 of lipids = 150  m 2

11. Data: Gorter and Grendel (1924) Red blood cell donor Surface area of cell membrane (  m 2 ) Surface area of extracted lipids (  m 2 ) Dog31.362 Sheep2.75.8 Rabbit4.99.8 Guinea pig0.521.02 Goat0.330.66 Human0.470.92

12. Was the prediction accurate? Come up with another model to fit the data.

14. Basic Lipid Bilayer

15. Refine the model FRAP (Fluorescence Recovery after Photobleaching) Lab technique where you attach a glowing (fluorescing) molecule to the head of a phospholipid, and then zap some of them with a laser so that the light goes out (permanently – those lipids can’t light back up)

17. The model so far Membrane is made of phospholipids, which have a water-loving head and two water- hating tails The phospholipids line themselves up in a double layer The phospholipids can shuffle around within the membrane.

19. Fat in food