The Working Cell: Membrane Function CHAPTER 5

1. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling

2. Membrane Function • Working cells must control the flow of materials to and from the environment. • A cell membrane or wrapper made of phospholipids is relatively impermeable • Proteins embedded in the membrane provide for selective permeability and transport of materials into and out of the cell, among other things Membrane Selectivity

3. Functions of Membrane Proteins Figure 5.11

4. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling

5. Passive Transport: Diffusion Across Membranes • Molecules contain heat energy. • They vibrate and wander randomly. • Diffusion is movement of molecules from regions of high concentration to low concentration • Molecules tend to spread into the available space. • Diffusion Across A Membrane • Passive transport of small or hydrophobic molecules • Facilitated diffusion of larger and polar molecules Diffusion

6. Examples of Passive Transport Across a Phospholipid Bilayer

7. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling

8. Osmosis and Water Balance in Cells • Osmosis is the passive transport of water across a selectively permeable membrane. • Water moves across a membrane from high concentration (high purity) to low concentration (low purity)

9. Terms Used to Compare the Purity of Water Solutions • A hypertonic solution • Has a higher concentration of dissolved substances (solute) 5% salt 1% salt • A hypotonic solution • Has a lower concentration of dissolved substances (solute) 1% salt 5% salt • An isotonic solution • Has an equal concentration of dissolved substances (solute). 1% salt 1% salt

10. Cells Must Regulate Salt and Water Balance Turgid Elodea Plasmolysis

11. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling

12. Active Transport: The Pumping of Molecules Across Membranes • Active transport requires energy to pump molecules across a membrane, into more a more crowded space • Active transport is the movement of molecules from low concentration to high concentration Active Transport

13. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling

14. Bulk Transport: Exocytosis and Endocytosis • Exocytosis • Dumping molecules out of the cell (export) Exocytosis and Endocytosis Introduction

15. Bulk Transport: Exocytosis and Endocytosis • Endocytosis • Bringing molecules into the cell (import) • Includes pinocytosis, phagocytosis, and receptor-mediated endocytosis Pinocytosis: cell “drinking” Phagocytosis: cell “eating”

16. Receptor-mediated endocytosis Receptor-Mediated Endocytosis

17. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling

18. The Role of Membranes in Cell Signaling • Cellular communication • Begins with the reception of an extracellular signal. 2. The signal is transduced or passed across the membrane 3. A response is elicited from the transduced signal

19. The Working Cell: Membrane Function CHAPTER 5 Membrane Function Passive Transport Osmosis and Water Balance Active Transport Bulk Transport Exo- and Endocytosis Cell Signaling