1. SURFACE TENSION

2. What’s going on at the surface of a liquid?

3. What’s going on at the surface of a liquid? Let’s take a look!

23. Particles that make up a liquid are in constant random motion; they are randomly arranged.

24. You might expect the particles at the surface, at the micro level, to form a random surface, as shown below.

25. You might expect the particles at the surface, at the micro level, to form a random surface, as shown below.

27. = intermolecular attractions But how do intermolecular forces influence the surface?

28. Under the surface, intermolecular attractions pull on individual molecules in all directions = intermolecular attractions

29. = intermolecular attractions

30. = intermolecular attractions

31. At the surface, pull on the molecules is laterally and downward; there is negligible intermolecular attractions above the molecules (from the medium above, such as air). SO, the net force on surface molecules is downward.

32. The result of this downward force is that surface particles are pulled down until counter-balanced by the compression resistance of the liquid:

35. Surface molecules are compressed more tightly together, forming a sort of skin on the surface, with less distance between them compared to the molecules below.

36. Surface molecules also form a much smoother surface than one would expect from randomly moving molecules.

39. This explains the characteristic rounded shape that liquids form when dropping through the air: The molecules are all being pulled toward the center.

40. This explains the characteristic rounded shape that liquids form when dropping through the air: The molecules are all being pulled toward the center.

41. Water in particular has a very high surface tension. What property does water have that would give it such a strong surface tension?

42. I. Membrane Structure II. Permeability III. Transport Across Membranes A. Passive B. Facilitated C. Active D. Bulk

43. Membrane structure 1915, knew membrane made of lipids and proteins Reasoned that membrane = bilayer Where to place proteins? Lipid layer 1 Lipid layer 2 Proteins

44. Membrane structure

45. freeze fracture proteins intact, one layer or other two layers look different Membrane structure

46. Experiment to determine membrane fluidity: marked membrane proteins mixed in hybrid cell Membrane structure

47. Membrane fluidity phospholipid f.a. “tails”: saturation affects fluidity cholesterol buffers temperature changes Membrane structure

48. “fluid mosaic model” – 1970s fluid – phospholipids move around mosaic – proteins embedded in membrane Membrane structure

49. cell membrane – amphipathic- hydrophilic & hydrophobic membrane proteins inserted, also amphipathic Membrane structure hydrophilic hydrophobic

50. Membrane Proteins Membrane proteins: - transmembrane – span membrane Integral: inserted in membrane Peripheral: next to membrane - inside or outside

51. Two transmembrane proteins: different structure Bacteriorhodopsin: proton pump Membrane structure Bacterial pore protein

52. Membrane Proteins

53. Movement of molecules Simple Diffusion: most basic force to move molecules Disperse until concentration equal in all areas

54. Small, non-polar molecules OK ex. steroids, O 2, CO 2 Movement of molecules Cell membranes only allow some molecules across w/out help: No charged, polar, or large molecules ex. sugars, ions, water*

55. Transport Across Membranes Types of transport: A.Passive transport - Simple diffusion - Facilitated diffusion - Osmosis B. Active transport C. Bulk transport Energy Required? Directionality?

56. DOWN concentration gradient molecules equally distribute across available area by type Passive Transport - Simple Diffusion - non-polar molecules (steroids, O 2, CO 2 ) NO ENERGY required

57. DOWN concentration gradient molecules equally distribute but cross membrane with the help of a channel (a) or carrier (b) protein. Passive Transport – Facilitated Diffusion NO ENERGY required

58. osmosis – movement of water across cell membrane water crosses cell membranes via special channels called aquaporins Passive Transport - Osmosis moves into/out of cell until solute concentration is balanced

59. Passive Transport - Osmosis equal solutes in solution as in cell more solutes in solution, than in cell fewer solutes in solution, than in cell In each situation below, does water have net movement, and which direction:

60. tonicity – # solutes in solution in relation to cell - isotonic – equal solutes in solution - hypertonic – more solutes in solution animal cell plant cell - hypotonic – fewer solutes in solution Passive Transport - Osmosis

61. Paramecium example regulate water balance water into contractile vacuole – water expelled pond water hypotonic Passive Transport - Osmosis

62. Scenario: in movie theater, watching a long movie. You are: drinking water You are: eating popcorn What happens to your blood? Passive Transport - Osmosis

63. transport proteins a. ion pumps (uniporters) Ex. Na-K ion pump - Na + ions: inside to out b. symporter/antiporter - K + ions: outside to in Active Transport UP/AGAINST concentration gradient ENERGY IS required antiporter: two molecules move opposite directions (UP gradient) c. coupled transport

64. ATP used pump H + ions out *gradients – used by cell for energy potential against concentration and charge gradients Active Transport - uniporter Ex. proton (H + ) pump uniporter: ONE molecule UP gradient

65. Active Transport – coupled transport Ex. Active glucose transporter Na+ diffusion used for glucose active transport Na+ moving DOWN concentration gradient Glucose moving UP concentration gradient coupled transport: one molecule UP gradient & other DOWN gradient (opposite directions)

66. phagocytosis – “food” in pinocytosis – water in Molecules moved IN - endocytosis Bulk Transport ENERGY IS required Several or large molecules

67. Bulk Transport receptor-mediated endocytosis – proteins bind molecules, vesicles inside Molecules moved OUT - exocytosis

68.  Self-Check Type of transport Energy required? Movement direction? Examples: Simple diffusionnoDown conc. gradientO 2, CO 2, non- polar molecules Osmosis Facilitated diffusion Active transport Bulk transport