1. Diploma In Microbiology MIC102 CHAPTER 2 Movement In And Out Of Cell Lecturer: Pn Aslizah Binti Mohd Aris 06-4832100 / 016-7377621

2. Chapter Outline Diffusion Osmosis & Active Transport Endocytosis - Phagocytosis - Pinocytosis Excocytosis

3. DIFFUSION Diffusion is the tendency for molecules to spread out evenly into the available space. Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movement in one direction. At dynamic equilibrium, as many molecules cross one way as cross in the other direction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Molecules of dye Membrane (cross section) WATER Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Equilibrium (b) Diffusion of two solutes The diffusion of solutes across a membrane

5. Two mode of diffusions: 1) Simple diffusion 2) Facilitated diffusion

6. Figure 4.17a Movement of Materials across Membranes Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration

7. Figure 4.17b-c Movement of Materials across Membranes Facilitated diffusion: Solute combines with a transporter protein in the membrane

8. Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another No work must be done to move substances down the concentration gradient The diffusion of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happen Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. Figure 4.18a Movement of Materials across Membranes Osmosis: The movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration Osmotic pressure: The pressure needed to stop the movement of water across the membrane

10. Figure 4.17d Movement of Materials across Membranes Through lipid layer Aquaporins (water channels)

11. Figure 4.18a–b The Principle of Osmosis

12. Figure 4.18c–e The Principle of Osmosis

13. Effects of Osmosis on Water Balance Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14. Lower concentration of solute (sugar) H2OH2O Higher concentration of sugar Selectively permeable membrane Same concentration of sugar Osmosis

15. Water Balance of Cells Without Walls Tonicity is the ability of a solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

16. Hypotonic solution (a) Animal cell LysedNormal Isotonic solution Shriveled Hypertonic solution H2OH2OH2OH2O H2OH2O H2OH2O

17. Hypertonic or hypotonic environments create osmotic problems for organisms Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments The protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump Video: Chlamydomonas Video: Chlamydomonas Video: Paramecium Vacuole Video: Paramecium Vacuole Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

18. Filling vacuole 50 µm (a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm. Contracting vacuole (b) When full, the vacuole and canals contract, expelling fluid from the cell.

19. Water Balance of Cells with Walls Cell walls help maintain water balance A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm) If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

20. Hypotonic solution (b) Plant cell Turgid (normal) Isotonic solution FlaccidPlasmolyzed Hypertonic solution H2OH2O H2OH2O H2OH2O H2OH2O

21. Plasmolysis In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22. Facilitated Diffusion: Passive Transport Aided by Proteins In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane Channel proteins include ◦ Aquaporins, for facilitated diffusion of water ◦ Ion channels that open or close in response to a stimulus (gated channels) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

23. EXTRACELLULAR FLUID Channel protein (a) A channel protein Solute CYTOPLAS M Solute Carrier protein (b) A carrier protein

24. Active transport uses energy to move solutes against their gradients Facilitated diffusion is still passive because the solute moves down its concentration gradient Some transport proteins, however, can move solutes against their concentration gradients Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

25. The Need for Energy in Active Transport Active transport moves substances against their concentration gradient Active transport requires energy, usually in the form of ATP Active transport is performed by specific proteins embedded in the membranes Active transport allows cells to maintain concentration gradients that differ from their surroundings The sodium-potassium pump is one type of active transport system Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

26. 2 EXTRACELLULAR FLUID [Na + ] high [K + ] low [Na + ] low [K + ] high Na + CYTOPLASM ATP ADP P Na + P 3 K+K+ K+K+ 6 K+K+ K+K+ 54 K+K+ K+K+ P P 1 The sodium-potassium pump: a specific case of active transport

27. Passive transport Diffusion Facilitated diffusion Active transport ATP

28. How Ion Pumps Maintain Membrane Potential Membrane potential is the voltage difference across a membrane Voltage is created by differences in the distribution of positive and negative ions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

29. Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane: ◦ A chemical force (the ion’s concentration gradient) ◦ An electrical force (the effect of the membrane potential on the ion’s movement) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

30. An electrogenic pump is a transport protein that generates voltage across a membrane The sodium-potassium pump is the major electrogenic pump of animal cells The main electrogenic pump of plants, fungi, and bacteria is a proton pump Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

31. Fig. 7-18 EXTRACELLULA R FLUID H+H+ H+H+ H+H+ H+H+ Proton pump + + + H+H+ H+H+ + + H+H+ – – – – ATP CYTOPLASM –

32. Cotransport: Coupled Transport by a Membrane Protein Cotransport occurs when active transport of a solute indirectly drives transport of another solute Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

33. Fig. 7-19 Proton pump – – – – – – + + + + + + ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Diffusion of H + Sucrose-H + cotransporter Sucrose

34. Bulk transport across the plasma membrane occurs by exocytosis and endocytosis Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles Bulk transport requires energy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

35. Exocytosis In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents Many secretory cells use exocytosis to export their products Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

36. Endocytosis In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane Endocytosis is a reversal of exocytosis, involving different proteins There are three types of endocytosis: ◦ Phagocytosis (“cellular eating”) ◦ Pinocytosis (“cellular drinking”) ◦ Receptor-mediated endocytosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

37. Phagocytosis & Pinocytosis In phagocytosis a cell engulfs a particle in a vacuole The vacuole fuses with a lysosome to digest the particle In, molecules are taken up when extracellular fluid is “gulped” into tiny vesicles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

38. In receptor-mediated endocytosis, binding of ligands to receptors triggers vesicle formation A ligand is any molecule that binds specifically to a receptor site of another molecule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

39. PHAGOCYTOSIS EXTRACELLULAR FLUID CYTOPLASM Pseudopodium “Food”or other particle Food vacuole PINOCYTOSIS 1 µm Pseudopodium of amoeba Bacterium Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM) Plasma membrane Vesicle 0.5 µm Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM) RECEPTOR-MEDIATED ENDOCYTOSIS Receptor Coat protein Coated vesicle Coated pit Ligand Coat protein Plasma membrane A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs) 0.25 µm

40. Movement of Substances Across Membranes Passive Transport: Cell expends no energy to move substances down a concentration gradient (high to low concentration) 1. Simple Diffusion 2. Facilitated Diffusion 3. Osmosis Active Transport: Cell expends energy from ATP, enabling it to transport substances against a concentration gradient

41. Simple Diffusion: The random movements of molecules cause them to spread out (diffuse) from an area of high concentration to area of low concentration

42. Facilitated Diffusion: Carrier protein molecules aid in the movement of substances through cell membrane from high to low concentration

43. Osmosis: The diffusion of water from an area of high water concentration to an area of low water concentration

44. Experiments that examine the effects of tonicity on osmosis

48. Active Transport: Carrier Protein molecules aid in movement of molecules against a concentration gradient

49. Endocytosis and Exocytosis Eukaryotic cells move substances by forming membrane-enclosed vesicles 1. Endocytosis: Form by invagination (poking in) and surrounding substances from outside the cell 2. Exocytosis: Vesicles inside the cell fuse with the plasma membrane and extrude contents from the cell

51. To be continued…..