MEMBRANE STRUCTURE AND TRAFFIC. Cell Membrane Structure and Function

Transcription

1 MEMBRANE STRUCTURE AND TRAFFIC Cell Membrane Structure and Function

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3 4.1 How Is the Structure of a Membrane Related to Its Function? The Plasma Membrane Isolates the Cell While Allowing Communication with Its Surroundings Membranes Are Fluid Mosaics in Which Proteins Move Within Layers of Lipids Unnumbered Figure 1 Phospholipid (p. 58) Unnumbered Figure 2 Phospholipid Bilayer (p. 58) Figure 4.1 The plasma membrane is a fluid mosaic (p. 59)

4 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 H 3 C CH 3 O N CH 2 CH 2 O P O CH 2 O CH 3 O HC O C CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH CH 2 CH CH 2 O H 2 C O C CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 head (hydrophilic) tails (hydrophobic)

5 phospholipid extracellular fluid (watery environment) hydrophilic heads bilayer hydrophobic tails hydrophilic heads cytoplasm (watery environment)

6 extracellular fluid (outside) glycoprotein binding site carbohydrate phospholipid bilayer cholesterol phospholipid receptor protein transport protein recognition protein cytoplasm (inside) protein filaments

7 4.1 How Is the Structure of a Membrane Related to Its Function? The Phospholipid Bilayer Is the Fluid Portion of the Membrane A Mosaic of Proteins Is Embedded in the Membrane

8 4.2 How Do Substances Move Across Membranes? Molecules in Fluids Move in Response to Gradients Figure 4.2 (Hide/Reveal) Diffusion of a dye in water (p. 61)

9 drop of dye water molecule

10 drop of dye water molecule

11 drop of dye water molecule

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14 4.2 How Do Substances Move Across Membranes? Movement Across Membranes Occurs by Both Passive and Active Transport Table 4.1 Transport Across Membranes (p. 62)

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16 4.2 How Do Substances Move Across Membranes? Passive Transport Includes Simple Diffusion, Facilitated Diffusion, and Osmosis Plasma Membranes Are Selectively Permeable to Diffusion of Molecules Some Molecules Move Across Membranes by Simple Diffusion Figure 4.3 (Hide/Reveal) Diffusion through the plasma membrane (p. 63)

17 Simple diffusion (extracellular fluid) lipid-soluble molecules (O 2, CO 2, H 2 O) Facilitated diffusion through a channel ions Facilitated diffusion through a carrier amino acids, sugars, small proteins (cytoplasm) channel protein (extracellular fluid) carrier protein (cytoplasm)

18 Simple diffusion lipid-soluble molecules (O 2, CO 2, H 2 O) (extracellular fluid) (cytoplasm)

19 Facilitated diffusion through a channel ions channel protein

20 Facilitated diffusion through a carrier amino acids, sugars, small proteins (extracellular fluid) carrier protein (cytoplasm)

21 Facilitated diffusion through a carrier amino acids, sugars, small proteins (extracellular fluid) carrier protein (cytoplasm)

22 Facilitated diffusion through a carrier amino acids, sugars, small proteins carrier protein

23 amino acids, sugars, small proteins

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25 4.2 How Do Substances Move Across Membranes? Other Molecules Cross the Membrane by Facilitated Diffusion, with the Help of Membrane Transport Proteins Osmosis Is the Diffusion of Water Across Membranes Figure 4.4 Osmosis (p. 64)

26 H 2 O selectively permeable membrane sugar pore selectively permeable membrane sugar molecule water molecule

27 H 2 O selectively permeable membrane sugar pore

28 selectively permeable membrane sugar molecule water molecule

29 4.2 How Do Substances Move Across Membranes? Osmosis Across the Plasma Membrane Plays an Important Role in the Lives of Cells Figure 4.5 The effects of osmosis (p. 65)

30 10 micrometers Isotonic solution Hypertonic solution Hypotonic solution

31 10 micrometers Isotonic solution

32 Hypertonic solution

33 Hypotonic solution

34 4.2 How Do Substances Move Across Membranes? Active Transport Uses Energy to Move Molecules Against Their Concentration Gradients Figure 4.6 (Hide/Reveal) Active transport (p. 66)

35 (extracellular fluid) 1 The transport protein binds both ATP and Ca Energy from ATP changes the shape of the transport protein and moves the ion across the membrane. 3 The protein releases the ion and the remnants of ATP (ADP and P) and closes. recognition site ATP ATP binding site ADP P Ca 2+ (cytoplasm)

36 (extracellular fluid) 1 The transport protein binds both ATP and Ca Energy from ATP changes the shape of the transport protein and moves the ion across the membrane. 3 The protein releases the ion and the remnants of ATP (ADP and P) and closes. recognition site ATP ATP binding site ADP P Ca 2+ (cytoplasm)

37 (extracellular fluid) 1 The transport protein binds both ATP and Ca 2+. recognition site ATP ATP binding site Ca 2+ (cytoplasm)

38 (extracellular fluid) 2 Energy from ATP changes the shape of the transport protein and moves the ion across the membrane. (cytoplasm)

39 (extracellular fluid) 3 The protein releases the ion and the remnants of ATP (ADP and P) and closes. ADP P (cytoplasm)

40 4.2 How Do Substances Move Across Membranes? Cells Engulf Particles or Fluids by Endocytosis Figure 4.7 Three types of endocytosis (p. 67)

41 Pinocytosis (extracellular fluid) Phagocytosis food particle pseudopods (extracellular fluid) 1 (cytoplasm) Receptor-mediated endocytosis 2 1 A dimple forms in the plasma membrane, which 2 deepens and surrounds the extracellular fluid. 3 The membrane encloses the extracellular fluid, forming a vesicle. nutrients receptors vesicle containing extracellular fluid 3 (extracellular fluid) 1 2 food (cytoplasm) vacuole 1 The plasma membrane extends pseudopods toward an extracellular particle (for example, food). 2 The ends of the pseudopods fuse, encircling the particle. 3 A vesicle called a food vacuole is formed containing the engulfed particle. 3 1 coated pit (cytoplasm) coated vesicle 1 Receptor proteins for specific molecules or complexes of molecules are localized at coated pit sites. 2 The receptors bind the molecules and the membrane dimples inward. 3 The coated pit region of the membrane encloses the receptor-bound molecules. 4 A vesicle ("coated vesicle") containing the bound molecules is released into the cytoplasm.

42 Pinocytosis (extracellular fluid) 1 (cytoplasm) 2 3 vesicle containing extracellular fluid 1 A dimple forms in the plasma membrane, which 2 deepens and surrounds the extracellular fluid. 3 The membrane encloses the extracellular fluid, forming a vesicle.

43 Pinocytosis (extracellular fluid) 1 (cytoplasm) 1 A dimple forms in the plasma membrane, which

44 Pinocytosis (extracellular fluid) 2 (cytoplasm) 2 deepens and surrounds the extracellular fluid.

45 Pinocytosis (extracellular fluid) 3 (cytoplasm) vesicle containing extracellular fluid 3 The membrane encloses the extracellular fluid, forming a vesicle.

46 Receptor-mediated endocytosis nutrients receptors (extracellular fluid) (cytoplasm) 1 coated pit coated vesicle 1 Receptor proteins for specific molecules or complexes of molecules are localized at coated pit sites. 2 The receptors bind the molecules and the membrane dimples inward. 3 The coated pit region of the membrane encloses the receptor-bound molecules. 4 A vesicle ("coated vesicle") containing the bound molecules is released into the cytoplasm.

47 Receptor-mediated endocytosis nutrients receptors (extracellular fluid) 1 coated pit (cytoplasm) 1 Receptor proteins for specific molecules or complexes of molecules are localized at coated pit sites.

48 Receptor-mediated endocytosis nutrients receptors (extracellular fluid) coated pit 2 (cytoplasm) coated vesicle 2 The receptors bind the molecules and the membrane dimples inward.

49 Receptor-mediated endocytosis nutrients receptors (extracellular fluid) coated pit 3 (cytoplasm) coated vesicle 3 The coated pit region of the membrane encloses the receptor-bound molecules.

50 Receptor-mediated endocytosis nutrients receptors (extracellular fluid) coated pit 4 (cytoplasm) coated vesicle 4 A vesicle ("coated vesicle") containing the bound molecules is released into the cytoplasm.

51 Phagocytosis food particle pseudopods (extracellular fluid) 1 2 (cytoplasm) food vacuole 1 The plasma membrane extends pseudopods toward an extracellular particle (for example, food). 2 The ends of the pseudopods fuse, encircling the particle. 3 A vesicle called a food vacuole is formed containing the engulfed particle. 3

52 (c) Phagocytosis food particle pseudopods (extracellular fluid) 1 1 (cytoplasm) food vacuole The plasma membrane extends pseudopods toward an extracellular particle (for example, food).

53 (c) Phagocytosis food particle pseudopods (extracellular fluid) 2 2 (cytoplasm) food vacuole The ends of the pseudopods fuse, encircling the particle.

54 (c) Phagocytosis food particle pseudopods (extracellular fluid) 3 (cytoplasm) food vacuole A vesicle called a food vacuole is formed containing the engulfed particle. 3

55 4.2 How Do Substances Move Across Membranes? Pinocytosis Moves Liquids into the Cell Receptor-Mediated Endocytosis Moves Specific Molecules into the Cell Figure 4.8 Receptor-mediated endocytosis (p. 67)

56 extracellular particles bound to receptors (extracellular fluid) coated vesicle (cytoplasm) protein coating coated pit plasma membrane 0.1 micrometer

57 extracellular particles bound to receptors (extracellular fluid) (cytoplasm) protein coating coated pit plasma membrane

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60 coated vesicle 0.1 micrometer

61 4.2 How Do Substances Move Across Membranes? Phagocytosis Moves Large Particles into the Cell Exocytosis Moves Material Out of the Cell Figure 4.9 Exocytosis (p. 68)

62 (extracellular fluid) plasma membrane secreted material plasma membrane vesicle (cytoplasm) 0.2 micrometer

63 (extracellular fluid) plasma membrane secreted material vesicle (cytoplasm)

64 secreted material plasma membrane vesicle 0.2 micrometer

65 4.3 How Are Cell Surfaces Specialized? Various Specialized Junctions Allow Cells to Connect and Communicate Desmosomes Attach Cells Together Figure 4.10 Cell attachment structures (p. 68)

66 Desmosome small intestine Tight junction urinary bladder cells lining small intestine cells lining bladder desmosome plasma membranes (edge view) protein filaments in cytoplasm

67 Desmosome small intestine cells lining small intestine desmosome plasma membranes (edge view) protein filaments in cytoplasm

68 T ight junction urinary bladder cells lining bladder plasma membranes (edge view)

69 4.3 How Are Cell Surfaces Specialized? Tight Junctions Make the Cell Leakproof Gap Junctions and Plasmodesmata Allow Communication Between Cells Figure 4.11 Cell communication structures (p. 69)

70 Gap junctions Plasmodesmata liver root liver cells root cells plasma membrane cell wall

71 Gap junctions liver liver cells plasma membrane

72 Plasmodesmata root root cells plasma membrane cell wall

73 4.3 How Are Cell Surfaces Specialized? Some Cells Are Supported by Cell Walls Figure 4.12 Plant cell walls (p. 69) Figure 4.13 Caribou browse on the frozen Alaskan tundra (p. 70)

74 primary cell wall secondary cell wall middle lamella plasma membrane cytoplasm

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