CHAPTER 3

1. CHAPTER 3 A TOUR OF THE CELL

2. Concept 3.3: CELL MEMBRANE

4. MEMBRANE STRUCTURE • Membranes keep eukaryotic cells organized • Partition the cell • Control the movement of substances into and out of the cell • Help maintain chemical environment for the cell

5. MEMBRANE STRUCTURE • Membranes are mainly composed of 2 layers of phospholipid molecules with protein molecules embedded in them • Also contain small amounts of cholesterol and carbohydrate molecules

6. PHOSPHOLIPIDS • Similar to lipid molecules, but have only two fatty acids instead of three • Two fatty acids at one end of molecule—tails—are hydrophobic • Other end—head—is hydrophilic; has phosphate group attached

7. Membrane Phospholipids

8. PHOSPHOLIPID STRUCTURE ALLOWS MEMBRANES TO FORM BOUNDARIES • Plasma membrane separates watery inside of cell from watery environment outside the cell • Phospholipids form a two layer “sandwich” of molecules—phospholipid bilayer—at boundaries that surround the cell or organelle

10. MEMBRANE PROTEINS • Two main types —Fig. 3.4; p. 80: 1. Intracellular Receptors- Inside the Cell 2. Membrane Receptors – Located in the cell membrane.

11. MEMBRANE PROTEINS • Perform most specific membrane functions 1. Enzyme activity 2. Cell-to-cell recognition 3. Cell signaling 4. Transport of materials

12. Concept 3.4: Diffusion and Osmosis

13. DIFFUSION • Diffusion: net movement of particles from an area of greater concentration to an area of lesser concentration • Permeable membranes: membranes that particles to freely pass through them until the concentration of particles is equal on both sides of the membrane—balance or equilibrium

14. Example of Diffusion

15. PASSIVE TRANSPORT • Selectively permeable membranes: allow some substances to cross more easily than others; block some completely • Cell membranes are selectively permeable; O2 and CO2 pass freely; H2O must pass through protein channels; other molecules pass only under specific conditions

16. PASSIVE TRANSPORT • Passive transport: diffusion of a substance across a membrane with noenergy expenditure by the cell

17. Simple Diffusion

18. TYPES OF PASSIVE TRANSPORT • Simple diffusion: passage of substance directly through the membrane—O2, CO2 • Facilitated diffusion: substances pass through a channel in a transport protein in the membrane—sugars, H2O, some ions

19. Passive Transport

20. TYPES OF PASSIVE TRANSPORT

21. OSMOSIS • Passive transport of water is so common that it is given a special name • Osmosis: passive transport of H2O across a selectively permeable membrane • Aqueous (water is the solvent) solutions are classified into 3 categories called osmotic solutions

22. Movement of Water

23. TYPES OF OSMOTIC SOLUTIONS • Hypertonic Solution: a solution whose solute concentration is higher than the solute concentration inside the cell - Animal cells will lose water and shrivel when placed in a hypertonic solution— water moves out of the cell

24. Cells placed in a hypertonic solution

25. TYPES OF OSMOTIC SOLUTIONS • Hypotonic Solution: a solution whose solute concentration is lower than the solute concentration inside the cell - Animal cells will swell and possibly burst when placed in a hypotonic solution—water moves into the cell

26. Cell placed in a hypotonic solution

27. TYPES OF OSMOTIC SOLUTIONS • Isotonic Solution: a solution whose solute concentration is equal to the solute concentration inside the cell - Animal cells retain their shape when placed in isotonic solutions—no net gain or loss of water inside the cell

28. Isotonic solution Water molecules move in and out of the cell at the same rate, and the cell retains it’s normal shape.

29. BEHAVIOR OF RED BLOOD CELLS IN DIFFERENT OSMOTIC SOLUTIONS

30. OSMOSIS & PLANT CELLS • Hypotonic environment: plant cells are firmest and healthiest - Cell wall prevents cell membrane from bursting • Isotonic environment: non-woody plants wilt • Hypertonic environment: membrane pulls away from cell wall—kills the cell

31. PLANT & ANIMAL CELLS IN DIFFERENT OSMOTIC SOLUTIONS

32. Concept 3.5: Active Transport, Endocytosis, and Exocytosis

33. ACTIVE TRANSPORT • Substance is moved from area of lower concentration to an area of higher concentration • Requires the cell to expend energy

34. ACTIVE TRANSPORT • Plays major role in maintaining cell’s chemical environment • Two major types: 1) solute pumping 2) large molecule transport

35. SOLUTE PUMPING • Specific membrane transport protein pumps a solute across the membrane • Energy is used to move solute from area of lower concentration to area of higher concentration • Solutes moved into cells and out of cells

36. SOLUTE PUMPING

37. LARGE MOLECULE TRANSPORT • Some particles are too large to move through the membrane • Must be packaged in membrane sacs called vesicles • Particle fuses with plasma membrane and is moved either into (endocytosis) or out of (exocytosis) the cell • Both processes require energy

38. TYPES OF ENDOCYTOSIS • Phagocytosis: cell membrane engulfs and takes in particle of solid material; “cell eating” • Pinocytosis: cell membranes engulfs and takes in small droplet of liquid; “celldrinking”

39. EXOCYTOSIS • Product of cell is exported • Requires energy

40. ENDOCYTOSIS • Material is brought into the cell • Requires energy

41. ENDOCYTOSIS & EXOCYTOSIS

42. PASSIVE vs. ACTIVE TRANSPORT