1. Chapter 2 cellular physiology

2. Cell : building block & function unit The cell is the basic unit of the body to carry out and control the functional processes of life. The cell is contained within a limiting membrane, and it consists of various organelles suspended in cytoplasm.

3. Schematic three-dimensional illustration of cell structures visible under an electron microscope

4. A cell is made up of three major parts: A plasma membrane: enclose the cell The nucleus: houses the cells genetic material Cytoplasm: contain highly specialized organelles

5. Cell membrane (plasma membrane) Functions: 1.Selective barrier 2.Containing enzyme system 3.Containing transport system 4.Containing specific recognition sites

6. membrane structure “Fluid mosaic model” LM: too thin to be seen EM: tri-laminar structure two dark layer one light middle layer Sandwich appearance

8. Structure of cell membrane

9. Composition of cell membrane Lipid (more) phospholipids+cholesterol(lesser) Protein Carbohydrates (lesser)

10. Phospholipids molecule Lipid Bilayer (phospholipids and cholesterols ) polar head- negatively charged;hydrophilic Nonpolar fatty acid tails;hydrophobic

11. Lipid Bilayer (phospholipids and cholesterols ) Lipid Bilayer Cell membrane separating ICF from ECF When in contact with water self-assembled

12. Characteristics of phospholipids -- Lipid bilayer ’s nature: not a rigid but fluid The phospholipids are not held together by chemical bonds -- Consistency: liquid cooking oil -- Twirl around;move about -- Flexible: The cell can change the shape e.g. the RBC

13. Cholesterol Contribute to the fluidity as well as the stability of the membrane prevent the fatty acid chains form packing together

14. Membrane protein integral (intrinsic) protein : ion channels peripheral (extrinsic) protein

15. Membrane protein function(P 53 ) Channels Carrier molecules Receptor sites Docking-marker acceptors Membrane-bound enzymes Cell adhesion molecules (CAMs) ……

16. Carbohydrates (located only at the outer surface and bond to protein and lipids)

17. Fluid mosaic model This view of membrane structure is known as the fluid mosaic model : membrane fluidity the ever-changing mosaic pattern of the proteins embedded within the lipid bilayer.

18. Fluid mosaic model The phospholipids, which are not held together by chemical bonds, are able to twirl around rapidly (more) The membrane protein stud or attach on the membrane (lesser) The carbohydrate was binding with lipid or protein

19. Membrane transport Lipid bilayer : - primary barrier, -selectively permeable

20. Permeable or impermeable Relative solubility in lipid uncharged or nonpolar molecules -highly lipid-soluble: O 2 CO 2 fatty acid Size of the particle Water-soluble ions less than 0.8nm in diameter: H 2 O glycerol ethanol

21. Force Passive force: don’t require energy(ATP) Active force:require energy(ATP)

22. Categories of Transport Across the Plasma Membrane --Active Transport Primary Active Transport Secondary Active Transport --Endocytosis and exocytosis Simple Diffusion Facilitated Diffusion --Passive transport No need ATP need ATP

23. Passive transport Diffusion: Physical process that occurs whenever there is a concentration difference across the membrane and the membrane is permeable to the diffusing substance AB AB Diffusion from A to B Diffusion from B to A Net diffusion Diffusion from A to B Diffusion from B to A No net diffusion Down a concentration gradient

24. Simple diffusion Related to the concentration gradient Movement is DOWN the concentration gradient ONLY (higher concentration to lower concentration) Rate of diffusion depends on (Fick’law of diffusion) factorRate of diffusion Concentration gradient of substance (ΔC) Permeability (P) Surface area of membrane (A) Molecular weight of substance (MW) Distance (thickness) (ΔX)

25. Simple diffusion Substances: –Non-polar molecules (0 2 ). –Lipid soluble molecules (steroids). –Small polar covalent bonds (C0 2 ). –H 2 0 (small size, lack charge).

26. Osmosis is the net diffusion of water down its own concentration gradient The solute concentration increases, the water concentration decreases correspondingly

27. Different cases If the membrane is permeable to the solute as well as to water the solute is able to move down its own concentration gradient in the opposite direction of the net water movement.

28. If the membrane is impermeable to the solute … Water movement alone till the concentrations of water and solute on the two sides of the membrane become equal.

29. If a nonpenetrating solute is present on side A and pure water is present on side B? The concentrations between the two compartments can never become equal.

30. Tonicity: refers to the effect on cell volume of the concentration of nonpenetrating solutes in the solution surrounding the cell. Isotonic solution:has the same concentration of nonpenetrating solutes as normal body cells. hypotonic solution hypertonic solution

31. Facilitated diffusion Definition: the diffusion of lipid insoluble or water soluble substance across the membrane down their concentration gradients by aid of membrane proteins (carrier or channel) Substances: K +, Na +, Ca 2+, glucose, amino acid, urea

32. Carrier-mediated Substance: glucose, amino acid Concept: Diffusion carried out by carrier protein Mechanism: a “ferry” or “shuttle” process

33. Characteristics of carrier-mediated diffusion Net movement depend on concentration gradient --specificity: with specific molecule only. -- competition : Molecules with similar chemical structures compete for carrier site. -- saturation: Carrier binding sites is limited

34. Simple diffusion Carrier-mediated Facilitated diffusion Rate of transportation into cell Concentration transported molecules in ECF

35. Channel-mediated

36. Characteristic of ion channel Specificity Gating Closed Outside Insid e Activated Inactivated

37. Channel type Voltage-gated channel Chemical-gated channel Mechanically-gated channel Water channel etc.

38. Voltage-gated channel The molecular conformation of the gate responds to the electrical potential across the cell membrane, this type of channel is called voltage-gated (or dependent) channel.

39. Voltage-gated Na+ channel

40. Na+ channel conformation Closed Outside Inside Activated Inactivated

41. Chemical-gated channel Some protein channel gates are opened by the binding of another molecule with the protein; this causes a conformational change in the protein molecule that opens or closes the gate. This is called chemical gating. This type of channel is called chemically-gated (or dependent) channel

42. N 2 -Ach receptor channel

44. Mechanically-gated channel Outside Inside membrane Inside membrane Outside stretch

45. Mechanically-gated channel When sound waves move the basilar membrane it moves the hair cells that are connected to it, but the tips of the hair cells are connected to the tectorial membrane so the they get bent.There are little mechanical gates on each hair cell that open when they are bent. K+ goes into the cell and Depolarizes the hair cell. (concentration of K+ in the endolymph is very high)

46. Water channels The structure of aquaporin (AQP)

47. Aquaporin Aquaporin are water channel that exclude ions Aquaporin are found in essentially all organisms, and have biological and medical importance

48. Water transportation through the membrane Simple diffusion Ion channel Water channel

49. Active transport Primary active transport Second active transport (Involving the use of a protein carrier and transport substance against its concentration gradient)

50. Primary active transport Iodine -- thyroid gland cells

51. the energy required is derived directly from the breakdown of ATP or some other high-energy phosphate compound and moves a substance uphill

52. Primary active transport

53. ATP is required in active transport to vary the affinity of the binding site when exposed on opposite sides of the plasma membrane. These active transport mechanisms are frequently called pumps. H+ pump; Ca++ pump Na+-K+ ATPase pump

54. Concentration gradient of Na + and K + ECF (m mol/L)ICF (m mol/L) Na + K+K+ 140.0 150.0 15.0 4.0

55. Na + -K + ATPase ( Na + pump, Na + -K + pump ) -- electrogenic pump

56. Physiological role of Na + -K + pump Maintaining Na + and K + concentration gradients across the membrane (transport Na + out of cell and pick up K + from the outside). Partly responsible for establishing negative electrical potential inside the cell ( moves 3 Na + outside and 2 K + inside) Controlling cell volume ( by controlling the concentration of solutes ) Providing energy for secondary active transport

57. Secondary Active Transport the energy required is derived indirectly from the breakdown of ATP. Rather it use “second hand” energy stored in the form of and ion concentration gradient The established by primary active transport permits the transport of other substance against their concentration gradient

58. Secondary Active Transport

60. Na + Low X out in Na + Low H + out in Na + co-transport counter-transport (symport) (antiport) e.g. glucose, in the same direction as the Na+. e.g. H+, in the opposite direction to the Na+. high low Na + high X high high H + low Na + Secondary Active Transport

61. Endocytosis and Exocytosis Exocytosis

62. Endocytosis

63. Summary Term : - Voltage-gated channel - Ligand-gated channel - co-transport and counter-transport - Primary Active Transport and Secondary Active Transport Describe the ways of membrane transport Describe the physiological role of sodium pump