7.3 Cell Boundaries

1. 7.3 Cell Boundaries

2. Fluid compartments in our bodies are separated by membranes

3. Composition of body fluids Greater number of osmotically active particles

4. Some organisms have a CELL WALL • Plants (cellulose) • Algae (polysaccharide) • Fungi (-chitin) • Prokaryotes(peptidoglycan)

5. Why have a cell wall? • Mechanical support • Protection • Cell-cell communication • Maintenance of structure (turgor) • Prevent water loss

6. Membranes

7. Where are membranes located? • Plasma membrane (double membrane) • Membrane-bound organelles (single or double) • Secret Universe • Introduction to cell membrane

8. Why do we need plasma membranes made Our cells inhabit an aqueous environment • …but they must let ‘stuff’ (nutrients, ions, molecules,waste products) in and out • …..and they need to communicate with each other… How is this achieved?....

9. Functions of the Cell membrane • Protective barrier • Cell-Cell signalling • Transport of nutrients, products and waste products • Localisation of function within organelles • Semi-permeable: controls entry and exit of substances • Self-sealing! • Flexible, mobile fluid mosaic Cell membrane function

10. Let’s meet the components of the cell membrane • Phospholipid bilayer • Cholesterol • Carbohydrates (glycoproteins) • Proteins • Let's build a membrane from scratch…

11. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

12. Membrane lipid composition varies Fat composition affects flexibility: membrane must be fluid & flexible % unsaturated fatty acids in phospholipids • keep membrane less viscous • cold-adapted organisms, like winter wheat increase % in autumn • cholesterol in membrane

13. Membrane Proteins • Proteins determine a membrane’s specific functions • Cell membrane & organelle membranes each have unique collections of proteins • Channels, pumps, receptors

14. Porin monomer H+ Retinal chromophore b-pleated sheets NH2 Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH Cytoplasm H+ Examples water channel in bacteria proton pump channel in photosynthetic bacteria function through conformational change (shape change)

15. Many Functions of Membrane Proteins Outside Plasma membrane Inside channels for passive transport Immobilised Enzyme Cell surfacereceptor (pumps) Cell adhesion Cell surface identity marker Attachment to thecytoskeleton

16. Membrane glycoproteins (carbohydrates) ‘Chemical identification cards’ Play a key role in cell-cell recognition • ability of a cell to distinguish one cell from another • Antigens • basis for rejection of foreign cells by immune system

17. Let’s Review… • John Kyrk Cell membrane

18. Movement across the Cell Membrane

19. How are substances transported into and out of the cell? • Simple Diffusion(passive) • Facilitated diffusion (Passive) • Osmosis • Active transport • Endocytosis • Exocytosis

20. Simple Diffusion 2nd Law of Thermodynamicsgoverns biological systems • universe tends towards disorder (entropy) • Diffusion • movement from highlow concentration

21. Diffusion Movement is from HIGH to LOW concentration • “passive transport” • no energy needed movement of water diffusion osmosis

22. Let’s watch some animations • Diffusion animation 1 • Diffusion animation 2

23. inside cell outside cell Diffusion through phospholipid bilayer What molecules can get through directly? • fats & other lipids • What molecules can NOT get through directly? • polar molecules • H2O • ions • salts, ammonia • large molecules • starches, proteins lipid salt NH3 sugar aa H2O

24. high low Facilitated Diffusion Diffusion through protein channels • channels move specific molecules across cell membrane • no energy needed facilitated = with help open channel = fast transport

25. Channels through cell membrane Membrane becomes semi-permeable with protein channels • specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3

26. Which substances are transported by facilitated diffusion? • Glucose • Urea • Amino acids • Animation

27. The Special Case of WaterMovement of water across the cell membrane

28. Osmosis is facilitated diffusion of water Facilitated diffusion of water from high concentration of water to low concentrationof wateracross a semi-permeable membrane

29. hypotonic hypertonic Concentration of water Direction of osmosis is determined by comparing total solute concentrations on either side of the membrane: • Hypertonic- more solute, less water • Hypotonic- less solute, more water • Isotonic- equal solute, equal water water net movement of water

30. freshwater balanced saltwater

31. Water passes through special water pores - Aquaporins

32. Aquaporins • Structure, function and dynamics of aquaporins Peter Agre John Hopkins Roderick MacKinnon Rockefeller

33. Active Transport

34. low high Active Transport • Cells may need to move molecules against concentration gradient • shape change transports solute from one side of membrane to other • protein “pump” • “costs” energy = ATP conformationalchange ATP “The Doorman”

35. Active transport • Many models & mechanisms ATP ATP antiport symport

36. Getting through cell membrane • Passive Transport • Simple diffusion • diffusion of nonpolar, hydrophobic molecules • lipids • high  low concentration gradient • Facilitated transport • diffusion of polar, hydrophilic molecules • through a protein channel • high  low concentration gradient • Active transport • diffusion against concentration gradient • low  high • uses a protein pump • requires ATP ATP

37. Transport summary simplediffusion facilitateddiffusion ATP activetransport

38. Endocytosis and exocytosis • ACTIVE processes for bulk transport • These processes are intimately dependent on lipid bilayer fluid mosaic nature of the cell membrane • Endocytosis – internalisation • Exocytosis - externalisaton • Phagocytosis: the intake of large particulate matter • Pinocytosis: intake of extracellular fluids

39. Endocytosis • A simple one... • McGRaw Hill phagocytosis

40. Exocytosis • Protein produced by the ribosomes enter the lumen of the ER • Protein exits the ER and enters the cis or trans side of the Golgi aparatus • Protein is modified through Golgi, and vesiculated • Vesicle moves to and fuses with the plasma membrane • Exocytosis

41. How about large molecules? • Moving large molecules into & out of cell • through vesicles & vacuoles • endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” • exocytosis exocytosis

42. Endocytosis fuse with lysosome for digestion phagocytosis non-specificprocess pinocytosis triggered bymolecular signal receptor-mediated endocytosis

43. Let’s look at membrane transport mechanisms in action…

46. Intravenous Fluid Therapy is often in the emergency room • Hypertonic saline (7.2% NaCl) • Isotonic glucose saline solution (5% glucose/ 0.45% NaCl) • Isotonic saline (0.9% saline) • (Blood, plasma, colloids)

47. Emergency Room therapy Oxygen delivered by mask

48. 0.9% isotonic saline

49. 7.2% hypertonic saline

50. Oxygen crosses the alveolar membrane by diffusion Explain how oxygen diffuses into cells