1. Ch 7 Membrane Structure and Function

2. - Boundary between intracellular compartments, living cells, and abiotic environment –Selectively permeable –Some molecules cross membranes more readily than others Cellular membrane -overall functions

4. Predominant constituent: phospholipids Amphipathic molecules: hydrophobic AND hydrophilic Membrane Structure Dispersed protein components Membrane organization and properties described by: Fluid Mosaic Model Singer and Nicolson 1972

5. LE 7-2 Hydrophilic head Hydrophobic tail WATER Organization of membrane phospholipids

6. Mosaic: something made of small pieces

7. LE 7-3 Hydrophilic region of protein Hydrophobic region of protein Phospholipid bilayer Mosaic: Proteins dispersed among phospholipids in membrane:

8. Freeze-fracture studies of the plasma membrane Frozen membrane split along the middle of the phospholipid bilayer using a knife Imaged by EM Supports mosaic part of model

9. LE 7-4 Knife Cytoplasmic layer Extracellular layer Cytoplasmic layer Plasma membrane Extracellular layer Proteins

10. The Fluidity of Membranes Phospholipids move laterally within the bilayer Some membrane proteins also drift laterally Rarely does a phospholipid flip-flop transversely across the membrane

11. LE 7-5a Lateral movement (~10 7 times per second) Flip-flop (~ once per month) Movement of phospholipids

12. Cool temp: membranes switch from fluid to more solid state Solidification depends on type of lipid What property of lipids would favor liquid versus solid state? Effects of Temperature on membranes

13. LE 7-5b Viscous Fluid Unsaturated hydrocarbon tails with kinks Membrane fluidity Saturated hydro- carbon tails Degree of saturation of fatty acid tails

14. Tends to moderate effects of temp. on membrane state At warm temperatures (such as 37°C), restrains movement of phospholipids At cool temperatures, maintains fluidity by preventing tight packing Steroid cholesterol also component of membranes

15. LE 7-5c Cholesterol Cholesterol within the animal cell membrane

16. Can drift within the bilayer –Proteins much larger than lipids--> move more slowly Cell fusion studies support fluidity of membrane proteins Movement of membrane proteins

17. LE 7-6 Membrane proteins Mixed proteins after 1 hour Hybrid cell Human cell Mouse cell

18. Membrane Proteins and Their Functions Proteins determine most of the membrane’s specific functions Peripheral membrane proteins –not embedded –attached to extracellular or cytoplasmic surface Integral membrane proteins –penetrate the hydrophobic core of bilayer –often span the membrane

19. LE 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Microfilaments of cytoskeleton Cholesterol Integral protein Peripheral proteins CYTOPLASMIC SIDE OF MEMBRANE EXTRACELLULAR SIDE OF MEMBRANE Glycolipid