5.6 Diffusion, Membranes, and Metabolism

Transcription

1 5.6 Diffusion, Membranes, and Metabolism Concentration of a substance Number of atoms or molecules in a given volume Concentration gradient of a substance A difference in concentration between two regions

2 Diffusion Diffusion Net movement of molecules to a region where they are less concentrated Diffusion rates are influenced by: Temperature Molecular size Gradients of pressure, charge, and concentration

3 Diffusion

4 dye dye water Fig. 5.16, p. 82

5 Diffusion and Membrane Permeability Selective Permeability

6 Oxygen, carbon dioxide, small nonpolar molecules, and some molecules of water cross a lipid bilayer freely. Glucose and other large, polar, water-soluble molecules, and ions (e.g., H +, Na +, K +, Cl, Ca ++ ) cannot cross on their own. lipid bilayer Fig. 5.17, p. 83

7 How Substances Cross Membranes: Diffusion, Passive and Active Transport

8 How Substances Cross Membranes: Endocytosis and Exocytosis

9 Concentration gradient high Diffusion Passive Transport Active Transport ATP low Fig. 5.18, p. 84

10 Endocytosis Exocytosis Fig. 5.18, p. 84

11 5.7 Working With and Against Gradients Many solutes cross membranes through transport proteins (open or gated channels) Facilitated diffusion (passive transport) does not require energy input Solute diffuses down its concentration gradient through a transporter Example: Glucose transporters

12 Facilitated Diffusion

13 Fig. 5.19, p. 85

14 Extracellular Fluid passive transport protein Lipid Bilayer Cytoplasm glucose, more concentrated outside cell than inside glucose transporter Fig. 5.19, p. 85

15 Fig. 5.19, p. 85

16 Active Transport Active transporters require ATP energy to move a solute against its concentration gradient Maintain gradients across cell membranes Example: Calcium pumps Cotransporters move two substances at the same time Example: Sodium-potassium pump

17 Active Transport: Calcium Pump

18 Fig. 5.20, p. 86

19 higher concentration of calcium ions outside cell compared to inside calcium pump The shape of the pump returns to its resting position. An ATP molecule binds to a calcium pump. Fig. 5.20, p. 86

20 Fig. 5.20, p. 86

21 ADP + P i The shape change permits calcium to be released to opposite side of membrane. A phosphate group and ADP are released. Calcium enters a tunnel through the pump, binds to functional groups inside. The ATP transfers a phosphate group to pump. The energy input causes the pump s shape to change. Fig. 5.20, p. 86

22 Animation: Active Transport (example of ATP-driven work) CLICK HERE TO PLAY

23 5.8 Which Way Will Water Move? Osmosis The diffusion of water across a selectively permeable membrane Water molecules follow their concentration gradient, influenced by solute concentration

24 Osmosis

25 hypotonic solution in first compartment hypertonic solution in second compartment Initially, the volumes of the two compartments are equal, but the solute concentration across the membrane differs. The fluid volume rises in the second compartment as water follows its concentration gradient and diffuses into it. Fig. 5.21, p. 86

26 Tonicity Relative concentrations of two solutes separated by a semipermeable membrane Hypertonic fluid (higher solute concentration) Hypotonic fluid (lower solute concentration) Isotonic solutions (two solutions with the same tonicity)

27 A Tonicity Experiment

28 2% sucrose solution 1 liter of distilled water 1 liter of 10% sucrose solution 1 liter of 2% sucrose solution Fig. 5.22, p. 87

29 Effects of Fluid Pressure Hydrostatic pressure (turgor) supports plants Exerts pressure on cell walls of plants Osmotic pressure The amount of hydrostatic pressure that can stop water from diffusing into a hypertonic solution

30 Osmosis and Hydrostatic Pressure

31 5.9 Membrane Traffic To and From the Cell Surface Exocytosis Cytoplasmic vesicle fuses with plasma membrane Contents are released outside Endocytosis Part of plasma membrane forms a vesicle that sinks into the cytoplasm

32 Three Types of Endocytosis Receptor-mediated endocytosis Substance binds to surface receptors Pit forms endocytotic vesicle Phagocytosis ( cell eating ) Amoebas use pseudopods to engulf prey Bulk-phase endocytosis Vesicle forms around extracellular fluid

33 Endocytosis and Exocytosis

34 Molecules get concentrated inside coated pits at the plasma membrane. Endocytosis Exocytosis coated pit The pits sink inward and become endocytic vesicles. Many of the sorted molecules cycle to the plasma membrane. Vesicle contents are sorted. Some vesicles and their contents are delivered to lysosomes. Some vesicles are routed to the nuclear envelope or ER membrane. Others fuse with Golgi bodies. Fig. 5.24, p. 88

35 Phagocytosis

36 Pseudopods surround a pathogen (brown). Endocytic vesicle forms. Lysosome fuses with vesicle; enzymes digest pathogen. Cell uses digested material or expels it. Fig. 5.26, p. 89

37 Other mechanisms move larger cargo across the plasma membrane Key Concepts: MEMBRANES AND METABOLISM Concentration gradients drive the directional movements of ions and molecules into and out of cells Transport proteins raise and lower water and solute concentrations across the plasma membrane and internal cell membranes

38 5.10 Night Lights Bioluminescence Fluorescent light released by enzyme-mediated reactions in organisms

39 Key Concepts: METABOLISM EVERYWHERE Knowledge about metabolism, including how enzymes work, can help you interpret what you see in nature