1. Chapter 8: Membrane Structure and Function Objectives The student is responsible for: 1.The definitions of all bold faced words in the chapter 2.Knowing the entire chapter.

2. Figure 8.1 Artificial membranes (cross sections) A phospholipid is amphipathic. Phospholipids will naturally form this lipid bilayer thus creating a thermodynam- ically stable boundary. Inside the cell Outside the cell

3. Figure 8.2 Two generations of membrane models (1935 – 1970’s)

4. Figure 8.3 Freeze-fracture and freeze-etch Freeze Fracture allowed researchers to view the split membrane with proteins interspersed within the lipids.

5. Figure 8.4 The fluidity of membranes Membranes are fluid!!!!

6. Figure 8.5 Evidence for the drifting of membrane proteins

7. Figure 8.6 The detailed structure of an animal cell’s plasma membrane, in cross section

8. Figure 8.7 The structure of a transmembrane protein Structure of a transmembrane protein: alpha helix in the hydrophobic portion

9. Figure 8.8 Sidedness of the plasma membrane Sidedness of the Plasma Membrane 1) external face is similar to inside of the golgi, ER and vesicles 2) CHOs that are made in ER, modified by the golgi end up on external surface.

10. Membrane CHOs are important for cell-cell recognition 1.Similar cell types (tissues) need to locate together and therefore they need to recognize each other as they are formed. 2.Foreign cells need to be rejected. 3.Small number of sugars are involved (15) 4.These can be glycolipids or glycoproteins 5.These molecules help to distinguish tissue from tissue in the same individual, same tissues between individuals and even from species to species. a)Blood groups of A, B, AB and O are due to these sugar differences.

11. Figure 8.9 Some functions of membrane proteins Functions of Membrane-Associated Proteins P. Membrane, organelle’s membrane Chloroplasts or mitochondrial Plasma membrane

12. Figure 8.10 The diffusion of solutes across membranes

13. Traffic Across Membranes Is Selective Selective Permeability applies to gases such as oxygen and carbon dioxide and ions, sugars, amino acids, basically all solutes. These substances also move through the membrane at different rates. Permeability of the Lipid Bilayer  Hydrophobic vs. Hydrophilic Transport Proteins  these allow for polar molecules and ions to avoid the hydrophobic core  the concentration gradient of that particular substance determines its direction of flow. Each solute follows its own gradient even though the total solute concentration may appear otherwise (fig. 8.10)  Passive transport does not require energy

14.  Bacteria possess membrane pores to take up fatty acids from their environment. The uptake of fatty acids is important for membrane structure, energy and as signaling molecules.  Yes, fatty acids still move across spontaneously.  It is unclear on the these transporters work for the fatty acids.  They do know it has a hydrophobic fatty-acid-binding pocket near the extracellular entrance. No channel connects this pocket to the inside of the cell; instead a hatch plugs the barrel-shaped protein that spans the membrane. It is hypothesized that the hatch changes shape to open up a passageway for the fatty acids to diffuses into the cell.  Source: Chemical and Engineering News, June 7, 2004, pg 30: http://www.CEN-ONLINE.ORGhttp://www.CEN-ONLINE.ORG  Researchers: HHMI researcher Tom Rapoport and postdoc Bert van den Berg of Harvard Medical School that crystallized this transporter.  Science, 304, 1506 (2004)

15. Figure 8.11 Osmosis Osmosis Direction of water flow is determined by total solute concentration, from hypotonic to hypertonic solution

16. Figure 8.12 The water balance of living cells Osmoregulation in Plant and Animal Cells

17. Figure 8.13 The contractile vacuole of Paramecium: an evolutionary adaptation for osmoregulation Osmoregulation in Paramecium Filled or filling vacuole Empty vacuole

18. Figure 8.14 Two models for facilitated diffusion Facilitated Diffusion FD requires a transport protein but no energy It is also specific for the solute it is transporting. Aquaporins: channels specific for water; Gated channels require a chemical or electrical stimulus. Channel Protein Some transporters change shape

19. Figure 8.15 The sodium-potassium pump: a specific case of active transport Uh Oh!!!!: The sodium-potassium pump: ( Will this hurt?) Movie

20. Figure 8.16 Review: passive and active transport compared A summary

21. Figure 8.17 An electrogenic pump Or in mitochondria and chloroplasts

22. Figure 8.18 Cotransport

23. Figure 8.19 The three types of endocytosis in animal cells Transport of Large Molecules

24. Receptor-Mediated Endocytosis a)Protein receptors are stuck in the membrane waiting to bind to a specific “ligand” or extracellular substance. b)The receptors are in specific regions called coated pits.coated pits c)Once the ligands bind to the receptors, the coated pit buds off into the cytoplasm, enters the cell and then digested. d)Advantage: take in large quantities of a solute even though it is not in high concentration in the extracellular environment. e)Example (a very important one) a)Cholesterol gets bound to two kinds of molecules in the blood stream: low-density lipoproteins (LDLs) or high-density lipoproteins (HDLs) b)Cholesterol bound LDLs bind to LDL receptors on liver cells; get transported into the cell and therefore removed from bloodstream. c)Hypercholesterolemia: LDL receptors are defective