Transport across membranes

1. Transport across membranes

2. Syllabus reference: Candidates should be able to:

3. This symbol in the corner of a slide indicates a picture, diagram or table taken from your text book

5. passive processes energy- requiring processes Transport across membranes • Diffusion (and osmosis) • Facilitated diffusion • Active transport • Membrane trafficking

6. Diffusion • Simple diffusion through the phospholipid bilayer

7. Diffusion animation

8. Fick’s Law Rate of diffusion =

9. Diffusion of water; Osmosis

10. Diffusion of water; Osmosis

11. Diffusion of water; Osmosis  = 0kPa

12. Diffusion of water; Osmosis

13. Osmosis Only free water molecules can diffuse through the membrane

14. In an environment that is hypotonic, the water concentration is greater outside the cell and the solute concentration is higher inside (the interior of the cell is hypertonic to the hypotonic surroundings). Water goes into the cell

15. In anisotonic environment, both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. There is no net change in water concentration

16. If the environment is hypertonic, the water concentration is greater inside the cell while the solute concentration is higher outside (the interior of the cell is hypotonic to the surrounding hypertonic environment). Water goes out of the cell

17. Osmosis; plant cells turgid cells flaccid cells • Turgor pressure in plant cells depends on osmosis

18. Osmosis; plant cells in high water potential

19. Osmosis; plant cells in low water potential

20. Osmosis; animal cells • Osmosis and blood cells

21. Osmosis; summary

22. Osmosis

24. Transport across membranes • The lipid bilayer is more permeable to non-polar molecules than to polar molecules and ions. • The size of a molecule also affects permeability – the lipid bilayer is more permeable to small molecules than to large molecules.

25. A protein molecule providing a channel through the membrane Double layer of lipid molecules Transport across membranes • Therefore if larger molecules and charged ions are to be transported there must be other mechanisms involved in crossing a membrane

26. Facilitated diffusion • Occurs through channel proteins • These proteins act as channels for ions • They can be open or closed • Different conditions may have to be satisfied for the channel to open

27. Channel protein

29. Diffusion & facilitated diffusion

30. Carrier protein

31. Channel proteins

32. Voltage gated animation

33. Ligand gated animation

35. Active transport carrier protein The energy released from ATP causes a change in the shape of the protein and the particles are deposited on the other side of the membrane The carrier protein picks up the particles from one side of the membrane • Active transport involves expenditure of energy • Substances are moved against a concentration gradient

36. Active transport

37. Active transport animation

38. Active transport; Ion pumps • The sodium-potassium pump

39. Active transport

41. Membrane trafficking

42. Membrane trafficking 1 2 3 4

43. Membrane trafficking

44. Endocytosis and exocytosis

45. Endocytosis & exocytosis

47. Endocytosis

48. Endocytosis • There are three types of endocytosis • pinocytosis [the endocytosis of dissolved substances and liquids] • phagocytosis [the engulfing of cells or particles] • receptor-mediated endocytosis [selective/ controlled endocytosis]

50. Endocytosis 1; pinocytosis pinocytosis = the endocytosis of dissolved substances and liquids