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CELL MEMBRANE FUNCTION PASSIVE DIFFUSION, OSMOSIS, FACILITATED DIFFUSION AND ACTIVE TRANSPORT The Cell Membrane Question of the Day: How Is the Structure of a Membrane Related to Its Function? MEMBRANE PROTEINS Signaling molecule Enzymes ATP (a) Transport Receptor Signal transduction (b) Enzymatic activity (c) Signal transduction (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM) Glycoprotein (d) Cell-cell recognition N-terminus C-terminus Helix EXTRACELLULAR SIDE CYTOPLASMIC SIDE Importance ER 1 1. Acquire molecules & Ions 2.Transport into and out of cell through membrane Transmembrane glycoproteins Secretory protein Glycolipid Golgi 2 apparatus Vesicle 3 4 3.Transport WITHIN the cell Secreted protein Plasma membrane: Cytoplasmic face Extracellular face Transmembrane glycoprotein Membrane glycolipid Cell Membrane Function Problems and Solutions 1. Relative concentrations Passive Transport Active Transport 2. Lipid bilayers are impermeable to most essential molecules and ions permeable to: small non polar molecules Cell membrane function, con’t b. impermeable to: - DIFFUSION SIMPLE DIFFUSION REQUIRES A CONCENTRATION GRADIENT FACILITATED DIFFUSION REQUIRES A CONCENTRATION GRADIENT AND A PROTEIN TRANSPORTER Use you membrane models to show diffusion Molecules of dye Membrane (cross section) WATER Net diffusion (a) Diffusion of one solute Net diffusion Equilibrium Net diffusion Net diffusion (b) Diffusion of two solutes Net diffusion Net diffusion Equilibrium Equilibrium Use your EXTRACELLULAR models to FLUID show facilitated diffusion. Channel protein Solute CYTOPLASM (a) A channel protein What molecules would you want to transport this way? Carrier protein (b) A carrier protein Solute ACTIVE TRANSPORT REQUIRES A PROTEIN TRANSPORTER AND ATP ENERGY Active transport: ATP EXTRACELLULAR FLUID Na+ [Na+] high [K+] low Na+ Na+ Na+ Na+ Na+ Na+ Na+ CYTOPLASM 1 Na+ [Na+] low [K+] high P ADP 2 ATP P 3 P P 6 5 4 – ATP EXTRACELLULAR FLUID + – + H+ H+ Proton pump H+ – + H+ H+ – + CYTOPLASM – H+ + – + H+ ATP – H+ + H+ Proton pump H+ – H+ + – H+ + H+ Diffusion of H+ Sucrose-H+ cotransporter H+ Sucrose – – + + Sucrose REVIEW Passive transport Active transport ATP Diffusion Facilitated diffusion Osmosis Passive Diffusion of Water Vocabulary: Hypertonic, hypotonic, isotonic, osmotic pressure, tonicity, turgid, flaccid, lyse. Hypotonic solution H2O Isotonic solution H2O H2O Hypertonic solution H2O (a) Animal cell Lysed H2O Normal H2O Shriveled H2O H2O (b) Plant cell Turgid (normal) Flaccid Plasmolyzed What would happen to the animal cells in each beaker? 100% Distilled Water 80% Water 20% Dissolved Substances 70% Water 30% Dissolved Substances Which way did the water move? 80% H2O 20% “stuff” 100% Distilled Water 0% dissolved substances Hypotonic solution Why did the cell get so big? Which way did the water move? 80% H2O 20% “stuff” 80% Water 20% Dissolved Substances Isotonic solution Why did the cell stay the same size? Which way did the water move? 80% H2O 20% “stuff” 70% Water 30% Dissolved Substances Hypertonic solution Why did the cell get so small? • Let’s look at what happens to your blood cells in the three different solutions: – Isotonic (equal) – Hypertonic (high) – Hypotonic (low) “Cell” 0.03 M sucrose 0.02 M glucose Environment: 0.01 M sucrose 0.01 M glucose 0.01 M fructose Lower concentration of solute (sugar) Higher concentration of sugar H2O Selectively permeable membrane Osmosis Same concentration of sugar Additional transport Mechanisms • Bulk Transport • Endocytosis – Phagocytosis – Pinocytosis • Receptor-mediated endocytosis http://www.youtube.com/watch?v=PsrnMeu6sIY&feature=related PHAGOCYTOSIS EXTRACELLULAR FLUID 1 µm CYTOPLASM Pseudopodium Pseudopodium of amoeba “Food” or other particle Bacterium Food vacuole Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM) Phagocytosis Amoeba • Your white bloods cells also do this. • This is the ingestion of large particles. PINOCYTOSIS 0.5 µm Plasma membrane Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM) Vesicle Pinocytosis • Tiny pockets form along cell membrane, and pinch off into vacuoles inside the cell. Sometimes called “Cell Drinking” RECEPTOR-MEDIATED ENDOCYTOSIS Coat protein Receptor Coated vesicle Coated pit Ligand A coated pit and a coated vesicle formed during receptormediated endocytosis (TEMs) Coat protein Plasma membrane 0.25 µm Exocytosis • This is how the cell gets rid of waste.