The Plasma Membrane -

1. The Plasma Membrane - Gateway to the Cell

2. Photograph of a Cell Membrane

3. How is the structure related to its function? • Isolates the cell, yet allows communicationwith its surroundings • “fluid mosaics” = proteins (and everything else) movewithin layers of lipids • Double layer • A barrier, binding site for enzymes, anchoring site, regulates transport in and out of cell • Helps maintain homeostasis

4. What is the bilayer made of? • 2 layers of phospholipids • Proteins (enzymes and channels) • Carbohydrates • Cholesterol (lipids)

5. FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

6. Membrane Components

7. Phospholipids Tails: 2 fatty acid chains that are nonpolar Head: contains a–PO4 group & glycerol, is polar

9. Solubility • Materials that are soluble in lipidscan pass through the cell membraneeasily • Hydrophobic can pass through easily • Hydrophilic can not

10. Semipermeable Membrane Smallmolecules and larger hydrophobic molecules move through easily. e.g. O2, CO2

11. Semipermeable Membrane Ions,hydrophilicmolecules larger than water, and large molecules such as proteinsdo not movethrough the membrane on their own.

12. Types of Transport Across Cell Membranes

13. Two types of transport Passive Transport Active Transport • Transport of molecules across the membrane from a high concentration to low concentration, requiring no cellular energy • Examples: • Simple Diffusion • Facilitated Diffusion • Osmosis • Transport of molecules across the membrane from a low concentration to high concentration, requiring energy • Examples: • Endocytosis • Exocytosis • “pumps”

14. Forms of Transport Across the Membrane

15. Passive Transport • Simple Diffusion • Doesn’t require energy • Moves high to low concentration • Example: Oxygen diffusing into a cell and carbon dioxide diffusing out.

16. Simple Diffusion

17. DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY

18. Diffusion of Liquids

19. Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW)

20. Osmosis Diffusion across a membrane • Diffusion of wateracross a membrane • Moves fromHIGH water potential(low solute) toLOW water potential(high solute) Semipermeable membrane

21. Diffusion of H2O Across A Membrane High H2O potentialLow solute concentration Low H2O potentialHigh solute concentration

22. Aquaporins • Water Channels • Protein pores used during OSMOSIS WATERMOLECULES

23. Types of Osmosis • 3 types (subcategories) • Isotonic Hypertonic Hypotonic

24. Cell in Isotonic Solution 10% NaCL90% H2O ENVIRONMENT CELL NO NET MOVEMENT 10% NaCL 90% H2O What is the direction of water movement? Dynamic equilibrium The cell is at _______________.

25. Cell in Hypertonic Solution 15% NaCl85% H2O ENVIRONMENT CELL 5% NaCl 95% H2O What is the direction of water movement?

26. Cell in Hypotonic Solution 10% NaCl90% H2O CELL 20% NaCl 80% H2O What is the direction of water movement?

27. Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) CYTOLYSIS PLASMOLYSIS

28. Cytolysis & Plasmolysis Plasmolysis Cytolysis

29. Osmosis in Red Blood Cells Isotonic Hypertonic Hypotonic

30. isotonic hypotonic hypertonic hypertonic isotonic hypotonic

31. Passive Transport • Facilitated diffusion • Doesn’t require energy • Uses transport proteins to move high to low concentration BUT needs some “guidance” • Examples: Glucose or amino acids moving from blood into a cell.

32. Types of Transport Proteins • Channel proteins are embedded in the cell membrane & have a pore for materials to cross • Carrier proteins can change shape to move material from one side of the membrane to the other

33. Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins.

34. Facilitated Diffusion • Some carrier proteins bond, then drag molecules to the other side

35. Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane

36. Active transport Needs energy!

37. Active Transport • Requires energy or ATP • Moves materials from LOW to HIGH concentration • AGAINST concentration gradient

38. Active transport • Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. • Called Na+-K+ Pump

39. Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

40. Moving the “Big Stuff” Exocytosis- moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another.

41. Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

42. Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis.

43. Pinocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle.

44. Pinocytosis • Cell forms an indention • Materials dissolve in water to be brought into cell • Called “Cell Drinking”

45. Example of Pinocytosis mature transport vesicle pinocytic vesicles forming Transport across a capillary cell (blue).

46. Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.

47. Receptor-Mediated Endocytosis

48. Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating”

49. Phagocytosis About to Occur

50. Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)