1. Biology 205 Lecture 05: Membranes Readings: DO NOT POST THESE LECTURES!!! INSTRUCTOR VERSIONS

2. Text Readings Chapter 6: ALL Chapter 35: Study figure 35.20 Chater 36: Study figures 36.10, 36.13 Chapter 37: Figure 37.7 Chapter 40: Figures 40.3, 40.4 Chapter 41: Figure 41.10 Chapter 43: Figure 43.3

3. Membranes compartmentalize Used universally to compartmentalize cells. Must be selectively permeable Must be able to grow Must be able to withstand dramatic shape changes and potential damage

4. Compartmentalization

6. Fatty acids: constituents of phospholipids

7. Hydrophobic molecules and water

8. Triacyglycerol: an energy-dense storage compound

9. Phospholipids: Phospholipids: fundamental constituents of biological membranes

10. membrane How phospholipids behave in water to produce a membrane

11. The Fluid-Mosaic model of membrane structure

12. fluidity Membrane fluidity Lots of this Not so much of this

13. fluidity Membrane fluidity

14. Degree of saturation Factors affecting fluidity: Degree of saturation Maximum number of hydrogens possible No double bonds Solid at room temp. Having one or more double bonds Tends to be liquid at room temp.

15. Cholesterol Factors affecting fluidity: Cholesterol

16. selectively permeable Biological membranes are selectively permeable

17. Membrane asymmetry What factors generate and maintain membrane asymmetry ?

18. How to cross a membrane (when you are stuck with polar bonds)

19. Transmembrane domains

21. Beta barrels Flexibility limitations

22. Nobel Alert! (2008) GFP: Green Fluorescent Protein zeiss-campus.magnet.fsu.edu

23. www.olympusmicro.com pubs.rsc.org

24. Two proteins, two functions, but highly similar structure! Green fluorescent protein Porin subunit Where would the hydrophobic amino acids be in each case? Soluble protein Membrane bound protein

25. Hydrophobicity plots

26. Disrupting membranes: detergents

27. Disrupting membranes

30. Sugar coatings: glycoproteins & glycolipids

31. glycocalyx

32. Membranes can form domains (subregions) Addition of lipid raft concentrating factor Edidin, M. (2003) Nat. Rev. Mol. Cell Biol. 4:414

33. Cell membranes are dynamic! Live Camera Action! Beads the size of molecules are conjugated with a fluorescent tag that lipids like to hang onto… Individual paths of lipids as they moved through the membrane can then be tracked

34. Cell membranes are dynamic! Live Camera Action! Beads the size of molecules are conjugated with a fluorescent tag that lipids like to hang onto… Individual paths of lipids as they moved through the membrane can then be tracked http://www.uni-ulm.de/nawi/nawi-biophys/forschung/schwerpunkte/nanostrukturen.html

35. FRAP Fluorescence Recovery After Photobleaching Label protein of interest with fluorescent tag, photobleach (burn out) with a laser and time how long it takes for burn out to recover

36. FRAP Fluorescence Recovery After Photobleaching photobleach % fluorescence X Y time (Y/X)100 = % recovery Slope of linear portion of recovery = lateral mobility

37. FRAP Fluorescence Recovery After Photobleaching Label protein of interest with fluorescent tag, photobleach (burn out) with a laser and time how long it takes for burn out to recover

38. Prion protein, no QN repeats (fused to GFP) Prion protein, WITH QN repeats (fused to RFP)

39. Bacterial membranes

40. Transport How do water soluble molecules get across a hydrophobic lipid bilayer? – Diffusion But what if the molecules are BIG and/or CHARGED? How is this traffic regulated? – Carrier (transport) proteins – Channel proteins

41. Active vs. Passive transport

42. what controls the direction?

43. Osmosis: the diffusion of water

45. Ion concentrations inside and outside cells: a balancing act: Membrane potential

46. What HAS to get through? Ions Sugars Amino acids Nucleotides Metabolites Signaling molecules Etc. etc. etc…… diff channels; specificity

47. Carrier (transport) ProteinsChannel Proteins moving parts hydrophillic pores

48. Glucose transporter

49. What about charged solutes? Net ~ negative INSIDE CELL Net ~ positive OUTSIDE CELL INTRACELLULAR MEDIUM EXTRACELLULAR MEDIUM

50. facilitated diffusion Channel proteins and facilitated diffusion

51. Active transport and energetics Membrane transporters Different from enzymes: Nothing catalyzed In common with enzymes: Energetic barrier to contend with Very specific Can be saturated

52. Bacteriorhodopsin light light -> proton gradient -> ATP!

53. Bacteriorhodopsin

54. Na + K + pump – an ATPase This transporter is generating a sodium ion gradient across the membrane that can be used to fuel the active transport of a second molecule

55. Secondary active transport PMID 21527736 GUT BLOOD Glucose

56. Active transport Required to move solutes AGAINST their electrochemical gradients

57. How about bigger stuff??? Exocytosis Endocytosis Pinocytosis – “cell drinking” Phagocytosis – “cell eating”

58. Learning Objectives (Lecture 05)