1. Membrane Transport

2. Surface Area and Volume of the Cell  The surface area of a cell is important for carrying out the cell’s functions –A small cell has more surface area relative to its cell volume and is more efficient –A cell has to be big enough to house DNA, proteins and other structures to survive and reproduce –Size of a cell is limited by –Having enough surface area to obtain sufficient nutrients and oxygen and to get rid of wastes –Also limited by the distance these materials must diffuse within a cell

3. 30 µm 10 µm Surface area of one large cube = 5,400 µm 2 Total surface area of 27 small cubes = 16,200 µm 2

4.  Large cells have more surface areas than smaller cells, BUT larger cells have less surface area relative to their volume than small cells of the same shape.  So larger cells have much smaller surface area relative to its volume when compared to smaller cells.  The need for a surface area large enough to service a cell’s volume explains the microscopic size of cells.

5. Watch this! MovieMovie So what are we saying? Smaller cells have a larger surface area to volume ratio This means that it is easier for them to move nutrients in and wastes out.

6. Membrane Structure The membrane is a fluid mosaic of phospholipids and proteins. It is a mosaic because of the diverse protein molecules embedded in the phospholipids. The membrane is fluid because molecules can drift in the membrane. ▫Fluidity due to the double bond of the phospholipid tails which prevents them from packing tightly together ▫Also from cholesterol found between the tails in animal cells.

7. Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein

8. Hydrophilic head WATER Hydrophobic tail WATER

9. Functions of the Membrane Helps with the framework of the cell Controls what goes in and out of the cell – selectively permeable –The membrane is selective due to its hydrophobic interior –Nonpolar molecules (carbon dioxide and oxygen) cross easily –Polar molecules (glucose and other sugars) do not cross easily

10. Parts of the Membrane Phospholipid bilayer Proteins Cholesterol Glycoproteins and Glycolipids

11. Cholesterol Glycoprotein Glycolipid Carbohydrate of glycoprotein Phospholipid Microfilaments of cytoskeleton Integrin

12. Phospholipids The membrane is made up of two layers of phospholipids The heads interact with the extracellular fluid and the cytoplasm The tails are sandwiched in between because they are hydrophobic. Allows for small hydrophobic molecules to pass right through

13. Proteins There are 2 types ▫Peripheral Proteins – These are found only on one side ▫Integral Proteins – Span the membrane. Also referred to as transmembrane proteins and integrins.  These proteins have to have both hydrophilic and hydrophobic parts

14. Integral Proteins Help with many activities of the cell Enzymes Cell to Cell Recognition Intercellular Junctions Transport Signal Transduction Helps to attach the cytoskeleton and the ECM

15. Enzymes

16. Messenger molecule Activated molecule Receptor

18. Cholesterol Found in between the phospholipid tails of animal cells Helps to keep the fluidity of the cell What else helps with this?

19. Glycoproteins and Glycolipids Are made up of carbohydrate chains ▫These chains can attach to proteins = glycoproteins ▫Or to lipids = glycolipid Help with cell – cell recognition ▫Serve as identification tags that are specifically recognized by membrane proteins of other cells ▫Enables cells of the immune system to recognize and reject foreign cells (bacteria)

20. Formation of Membranes Phospholipids were probably one of the first organic molecules to form on Earth They can spontaneously self-assemble to form membranes All cells have membranes

21. Water-filled bubble made of phospholipids

22. Water

23. Transport Across A Membrane

24. Transport Across a Membrane Passive – no energy is needed ▫Diffusion ▫Osmosis ▫Facilitated diffusion Active - energy is required ▫Sodium Potassium Ion Exchange Pump

25. Passive Transport

26. Diffusion Molecules tend to spread out evenly Molecules will move from where there is a high concentration to where there is a lower concentration Molecules vibrate and move randomly due to heat Molecules tend to move down their concentration gradient

27. Molecules will tend to move until they are about equal on both sides – dynamic equilibrium ▫Molecules will still move back and forth but there will be NO net change Diffusion is how most molecules move across a membrane.

28. Molecules of dye MembraneEquilibrium

29. Two different substances MembraneEquilibrium

30. Osmosis It is crucial for cells that water moves across their membrane Water moves across membranes in response to solute concentration inside and outside of the cell by a process called osmosis Osmosis will move water across a membrane down its concentration gradient until the concentration of solute is equal on both sides of the membrane Osmosis is the diffusion of water across a selectively permeable membrane

31. Osmosis Water moves from the solution with the lower solute concentration and more free water molecules to that with the higher solute concentration and fewer free water molecules

32. Selectively permeable membrane Solute molecule Lower concentration of solute H2OH2O Solute molecule with cluster of water molecules Net flow of water Water molecule Equal concentration of solute Higher concentration of solute

33. Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water –Tonicity is dependent on the concentration of a nonpenetrating solute on both sides of the membrane –Isotonic indicates that the concentration of a solute is the same on both sides –Cells lose and gain water at the same rate –Volume in animal cells will stay the same –Plants will be limp (flaccid)

34. –Hypertonic indicates that the concentration of solute is higher outside the cell –Cell can shrivel and die –Plants cells go through plasmolysis because the cell shrivels up and pulls away from the cell wall. –Hypotonic indicates a higher concentration of solute inside the cell –Animal cells gain water and may lyse –Plant cells are turgid (firm). Cell wall prevents the cell from bursting.

35. Isotonic solution (B) Lysed(C) Shriveled (D) Flaccid(E) Turgid (F) Shriveled Hypertonic solution Hypotonic solution Plant cell Animal cell (A) Normal Plasma membrane (plasmolyzed)

36. Watch this! Osmosis animation Use the information in the video to explain what happened to the cells in the plasmolysis lab

37. Osmoregulation – a process by which organisms are able to maintain water balance within their cells –This process prevents excessive uptake or excessive loss of water –Plant, prokaryotic, and fungal cells have different issues with osmoregulation because of their cell walls

38. Problems? Naah. You place a dialysis bag with 20% sucrose in a beaker of 15 % NaCl. What direction will the water move? What about the sugar? The salt? Which solution is hypertonic and which is hypo?

39. More problems. You place a piece of celery into salt water and into distilled water. What will happen to the weight of the celery in each case? Why? Explain which conditions are hypotonic and which are hypertonic.

40. Best Guess What happens to a cell in a hypertonic solution? What kind of solution would be good to have if you have to get an IV? Why does Gatorade taste like orange-flavored sweat?

41. Facilitated Diffusion Diffusion of molecules across a membrane through transport proteins Does not require energy because the molecules move down their concentration gradient Helps with the movement of polar and charged molecules across the membrane Driving source – concentration gradient Seen with sugars, amino acids, ions, and water (aquaporins – protein for water movement)

42. Facilitated Diffusion Transport proteins ▫Are specific for the solutes they transport ▫Some are hydrophilic channels that are used like a tunnel ▫Others bind the molecules, change shape and release the molecule on the other side ▫VideoVideo

43. Solute molecule Transport protein

44. Active Transport

45. Energy (ATP) is used because molecules move against their concentration gradient. Cells have a mechanism for moving a solute against its concentration gradient The mechanism alters the shape of the membrane protein through phosphorylation using ATP Na – K Ion Exchange Pump

46. Transport protein Solute Solute binding 1

47. Transport protein Solute Solute binding 1 Phosphorylation 2

48. Transport protein Solute Solute binding 1 Phosphorylation 2 Transport 3 Protein changes shape

49. Transport protein Solute Solute binding 1 Phosphorylation 2 Transport 3 Protein changes shape Protein reversion 4 Phosphate detaches

50. Diffusion Requires no energy Passive transport Higher solute concentration Facilitated diffusion Osmosis Higher water concentration Higher solute concentration Requires energy Active transport Solute Water Lower solute concentration Lower water concentration Lower solute concentration

51. Transport of Large Molecules A cell uses two mechanisms for moving large molecules across membranes –Exocytosis is used to export bulky molecules, such as proteins or polysaccharides –Endocytosis is used to import substances useful to the livelihood of the cell In both cases, material to be transported is packaged within a vesicle that fuses with the membrane Animation

52. There are three kinds of endocytosis –Phagocytosis is engulfment of a particle by wrapping cell membrane around it, forming a vacuole –Pinocytosis is the same thing except that fluids are taken into small vesicles –Receptor-mediated endocytosis is where receptors in a receptor-coated pit interact with a specific protein, initiating formation of a vesicle Cholesterol – goes through this –VideoVideo

53. Phagocytosis EXTRACELLULAR FLUID Pseudopodium CYTOPLASM Food vacuole “Food” or other particle Food being ingested

54. Pinocytosis Plasma membrane Vesicle Plasma membrane

55. Coated vesicle Coated pit Specific molecule Receptor-mediated endocytosis Coat protein Receptor Coated pit Material bound to receptor proteins Plasma membrane