1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 5 The Working Cell

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.14 Passive transport is diffusion across a membrane Diffusion is the tendency for particles to spread out evenly in an available space – From an area of high concentration to an area of low concentration Passive transport across membranes occurs when a molecule diffuses down a concentration gradient Small nonpolar molecules such as O 2 and CO 2 diffuse easily across the phospholipid bilayer of a membrane

3. LE 5-14a Molecules of dye Membrane Equilibrium

4. LE 5-14b Equilibrium

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Diffusion Animation: Diffusion

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.15 Transport proteins may facilitate diffusion across membranes In facilitated diffusion – Transport proteins that span the membrane bilayer help substances diffuse down a concentration gradient To transport the substance, a transport protein may – Provide a pore for passage – Bind the substance, change shape, and then release the substance

7. LE 5-15 Solute molecule Transport protein

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.16 Osmosis is the diffusion of water across a membrane In osmosis water, molecules diffuse across a selectively permeable membrane – From an area of low solute concentration – To an area of high solute concentration – Until the solution is equally concentrated on both sides of the membrane The direction of movement is determined by the difference in total solute concentration – Not by the nature of the solutes Animation: Osmosis Animation: Osmosis

9. LE 5-16 Water molecule Selectively permeable membrane Solute molecule H2OH2O Lower concentration of solute Higher concentration of solute Equal concentration of solute Solute molecule with cluster of water molecules Net flow of water

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.17 Water balance between cells and their surroundings is crucial to organisms Osmoregulation is the control of water balance Tonicity is the tendency of a cell to lose or gain water in solution – Isotonic solution: solute concentration is the same in the cell and in the solution No osmosis occurs Animal cell volume remains constant; plant cell becomes flaccid

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Hypotonic solution: solute concentration is greater in the cell than in the solution Cell gains water through osmosis Animal cell lyses; plant cell becomes turgid – Hypertonic solution: solute concentration is lower in the cell than in the solution Cell loses water through osmosis Animal cell shrivels; plant cell plasmolyzes

12. LE 5-17 Isotonic solution Hypotonic solution Hypertonic solution H2OH2O H2OH2O (1) Normal (2) Lysed H2OH2O H2OH2O H2OH2O H2OH2O Animal cell Plant cell (4) Flaccid(5) Turgid(6) Shriveled (plasmolyzed) (3) Shriveled Plasma membrane H2OH2O H2OH2O

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Video: Plasmolysis Video: Plasmolysis Video: Turgid Elodea Video: Turgid Elodea

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.18 Cells expend energy for active transport Active transport requires energy to move solutes against a concentration gradient – ATP supplies the energy – Transport proteins move solute molecules across the membrane Animation: Active Transport Animation: Active Transport

15. LE 5-18 Transport protein Solute ATP P ADP Protein changes shape P Solute bindingPhosphorylation Transport Protein reversion Phosphate detaches P

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a cell membrane – A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis) – Membranes may fold inward, enclosing material from the outside (endocytosis)

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a cell membrane – A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis) – Membranes may fold inward, enclosing material from the outside (endocytosis)

18. LE 5-19a Vesicle Fluid outside cell Protein Cytoplasm

19. LE 5-19b Vesicle forming

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endocytosis can occur in three ways – Phagocytosis ("cell eating") – Pinocytosis ("cell drinking") – Receptor-mediated endocytosis

21. LE 5-19c Pseudopodium of amoeba Phagocytosis Plasma membrane Food being ingested Material bound to receptor proteins PIT Cytoplasm Receptor-mediated endocytosis TEM 54,000  TEM 96,500  LM 230  Pinocytosis

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Receptor-Mediated Endocytosis Animation: Receptor-Mediated Endocytosis Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis Animation: Exocytosis Animation: Pinocytosis Animation: Pinocytosis Animation: Phagocytosis Animation: Phagocytosis

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 5.20 Faulty membranes can overload the blood with cholesterol Cholesterol is carried in the blood by low- density lipoprotein (LDL) particles Normally, body cells take up LDLs by receptor- mediated endocytosis Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors – People with hypercholesterolemia have more than twice the normal level of blood cholesterol

24. LE 5-20 Phospholipid outer layer LDL particle Cholesterol Protein Plasma membrane Receptor protein Vesicle Cytoplasm