A Closer Look at Cell Membranes. Chapter 5 Part 2

Transcription

1 A Closer Look at Cell Membranes Chapter 5 Part 2

2 5.5 Membrane Trafficking By processes of endocytosis and exocytosis, vesicles help cells take in and expel particles that are too big for transport proteins, as well as substances in bulk Membrane trafficking Formation and movement of vesicles formed from membranes, involving motor proteins and ATP

3 Exocytosis and Endocytosis Exocytosis The fusion of a vesicle with the cell membrane, releasing its contents to the surroundings Endocytosis The formation of a vesicle from cell membrane, enclosing materials near the cell surface and bringing them into the cell

4 Endocytosis and Exocytosis

5 Endocytosis Exocytosis A Molecules get concentrated inside coated pits at the plasma membrane. coated pit B The pits sink inward and become endocytic vesicles. C Vesicle contents are sorted. F Some vesicles and their contents are delivered to lysosomes. D Many of the sorted molecules cycle to the plasma membrane. E Some vesicles are routed to the nuclear envelope or ER membrane. Others fuse with Golgi bodies. lysosome Golgi Fig. 5-12, p. 86

6 Three Pathways of Endocytosis Bulk-phase endocytosis Extracellular fluid is captured in a vesicle and brought into the cell; the reverse of exocytosis Receptor-mediated endocytosis Specific molecules bind to surface receptors, which are then enclosed in an endocytic vesicle Phagocytosis Pseudopods engulf target particle and merge as a vesicle, which fuses with a lysosome in the cell

7 Receptor-Mediated Endocytosis

8 plasma membrane aggregated lipoproteins Fig. 5-13, p. 86

9 Animation: Phagocytosis

10 Phagocytosis

11 A Pseudopods surround a pathogen ( brown ). Fig. 5-14a, p. 87

12 B Endocytic vesicle forms. C Lysosome fuses with vesicle; enzymes digest pathogen. D Cell uses the digested material or expels it. Fig. 5-14b, p. 87

13 Membrane Cycling Exocytosis and endocytosis continually replace and withdraw patches of the plasma membrane New membrane proteins and lipids are made in the ER, modified in Golgi bodies, and form vesicles that fuse with plasma membrane

14 Exocytic Vesicle

15 A Molecules get concentrated inside coated pits at the plasma membrane. Endocytosis Exocytosis B The pits sink inward and become endocytic vesicles. coated pit D Many of the sorted molecules cycle to the plasma membrane. C Vesicle contents are sorted. E Some vesicles are routed to the nuclear envelope or ER membrane. Others fuse with Golgi bodies. F Some vesicles and their contents are delivered to lysosomes. lysosome Golgi Stepped Art Fig. 5-12, p. 86

16 Animation: Membrane cycling

17 5.5 Key Concepts: Membrane Trafficking Large packets of substances and engulfed cells move across the plasma membrane by processes of endocytosis and exocytosis Membrane lipids and proteins move to and from the plasma membrane during these processes

18 5.6 Which Way Will Water Move? Water diffuses across cell membranes by osmosis Osmosis is driven by tonicity, and is countered by turgor

19 Osmosis Osmosis The movement of water down its concentration gradient through a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration Tonicity The relative concentrations of solutes in two fluids separated by a selectively permeable membrane

20 Tonicity For two fluids separated by a semipermeable membrane, the one with lower solute concentration is hypotonic, and the one with higher solute concentration is hypertonic Water diffuses from hypotonic to hypertonic Isotonic fluids have the same solute concentration

21 Osmosis

22 hypotonic solution hypertonic solution solutions become isotonic selectively permeable membrane A Initially, the volume of fluid is the same in the two compartments, but the solute concentration differs. B The fluid volume in the two compartments changes as water follows its gradient and diffuses across the membrane. Fig. 5-16, p. 88

23 Animation: Tonicity and water movement

24 Experiment: Tonicity

25 Fig. 5-17a, p. 89

26 2% sucrose 2% sucrose 10% sucrose water A What happens to a semipermeable membrane bag when it is immersed in an isotonic, a hypertonic, or a hypotonic solution? Fig. 5-17a, p. 89

27 2% sucrose 2% sucrose 10% sucrose water A What happens to a semipermeable membrane bag when it is immersed in an isotonic, a hypertonic, or a hypotonic solution? B Red blood cells in an isotonic solution do not change in volume. C Red blood cells in a hypertonic solution shrivel because water diffuses out of them. D Red blood cells in a hypotonic solution swell because water diffuses into them. Stepped Art Fig. 5-17, p. 89

28 Fig (b-d), p. 89

29 B Red blood cells in an isotonic solution do not change in volume. C Red blood cells in a hypertonic solution shrivel because water diffuses out of them. D Red blood cells in a hypotonic solution swell because water diffuses into them. Fig (b-d), p. 89

30 Animation: Osmosis experiment

31 Effects of Fluid Pressure Hydrostatic pressure (turgor) The pressure exerted by a volume of fluid against a surrounding structure (membrane, tube, or cell wall) which resists volume change Osmotic pressure The amount of hydrostatic pressure that can stop water from diffusing into cytoplasmic fluid or other hypertonic solutions

32 Hydrostatic Pressure in Plants

33 Fig. 5-18a, p. 89

34 5.6 Key Concepts: Osmosis Water tends to diffuse across selectively permeable membranes, to regions where its concentration is lower

35 Animation: Active transport

36 Animation: Endocytosis and exocytosis

37 Animation: Fluid mosaic model

38 Animation: Passive transport II

39 Animation: Solute concentration and osmosis

40 Video: One bad transporter and cystic fibrosis

41 Video: Diffusion of dye in water

42 Video: Contractile vacuole