* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Survey
Document related concepts
Cytoplasmic streaming wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cell nucleus wikipedia , lookup
Theories of general anaesthetic action wikipedia , lookup
Cell encapsulation wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
SNARE (protein) wikipedia , lookup
Membrane potential wikipedia , lookup
Model lipid bilayer wikipedia , lookup
Lipid bilayer wikipedia , lookup
Cytokinesis wikipedia , lookup
Ethanol-induced non-lamellar phases in phospholipids wikipedia , lookup
Signal transduction wikipedia , lookup
List of types of proteins wikipedia , lookup
Transcript
5 Life’s Border The Plasma Membrane 5.1 The Importance of Activity at the Cell’s Periphery 5.2 Why Do We Need the Plasma Membrane? 5.3 Four Components of the Plasma Membrane 5.4 Moving Materials In and Out: Diffusions and Gradients 5.5 How Do Materials Get In and Out of the Cell? 5.6 Getting the Big Stuff In and Out Essay How Did We Learn? The Fluid-Mosaic Model of the Plasma Membrane LECTURE OUTLINE I. Introduction A. Importance of the plasma membrane (seen in malfunctioning transport in cystic fibrosis) B. Overview of major functions: 1. Keeping the goods concentrated, while keeping harmful materials out, requires transport in two directions 2. Communication with other cells II. Four Components of the Plasma Membrane A. Phospholipid Bilayer 1. Phospholipids: two fatty-acid chains and a polar phosphate group attached to glycerol: 2. Arrangement of phospholipids in water (two layers, heads pointed out, tails pointed in): 3. Permeability of bilayer: lipid center is a barrier to passage of large hydrophilic molecules, but it allows nonpolar, hydrophobic molecules to pass. B. Cholesterol (prevents passage of some small molecules and adds fluidity): C. Proteins: integral (span entire membrane) and peripheral (lie on either side) with diverse range of functions: 1. Structural support—attach to cytoskeleton 2. Recognition—helps immune system determine self from foreign (that’s why we reject transplants; good figures to show this in Scientific American July 1997 article on xenotransplantation). 3. Communication—receptors and binding sites 4. Transport—allow molecules to pass D. Glycocalyx—sugar components protruding from lipids and proteins, functions: 1. Binding sites for proteins in communication and recognition 2. Lubricate cells 3. Stick cells down III. Moving Materials In and Out: Diffusion and Gradients A. Random Movement and Diffusion: 1. Diffusion = movement of molecules from region of higher to lower concentration 2. Concentration gradient = difference between the highest and lowest concentration of a solute; like bike coasting downhill, the tendency is for molecules to travel from high to low concentration. B. Diffusion through Membranes C. Permeability verses semipermeability. Why certain molecules pass through membranes. D. Osmosis = net movement of water across a semipermeable membrane from an area of lower solute concentration to higher solute concentration: E. Importance of osmosis to membrane function in animals (drinking seawater) and plants (turgid pressure): IV. Two Main Types of Transport across Cell Membranes A. Passive Transport 1. Simple diffusion (water, gases, fat soluble) membrane is permeable, so they travel down concentration gradient and enter without energy output by cell: 2. Facilitated diffusion (larger polar molecules) membrane is impermeable, so even if they want to travel down the concentration gradient, they can’t without help from a membrane channel (transport protein): B. Active Transport: if molecules have to pass across the membrane up their concentration gradient, they cannot use the energy of diffusion, but must expend energy (ATP): 1. Na-K pump: 2. All three types of transport through membranes are compared in an animation V. Getting the Big Stuff In and Out A. Exocytosis: movement of materials out of the cell by fusion of vesicles with the plasma membrane (export or removal of wastes in single-celled organisms) B. Endocytosis: infolding of the plasma membrane to bring large materials into the cell C. Pinocytosis: “cell drinking”—water and solvents are enclosed in invaginating vesicle, used in digestive tract: D. Receptor-mediated endocytosis: more specific with receptor capturing ligand and concentrating into an invaginating pit: E. Phagocytosis: “cell eating”—how the human immune system ingests whole bacteria, or one-celled creatures eat using pseudopodia,