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

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

Functions of Membrane Proteins Figure 5.11

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

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

Examples of Passive Transport Across a Phospholipid Bilayer

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

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)

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

Cells Must Regulate Salt and Water Balance Turgid Elodea Plasmolysis

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

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

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

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

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

Receptor-mediated endocytosis

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

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

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