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Outline - Membranes 1. Fluid Mosaic Model of Membrane Structure 2. Membrane Proteins 1. Kinds of membrane proteins 2. Membrane protein structure Single pass Multi-pass: Channels, Pores & Carriers 3. Transport Mechanisms Passive: Diffusion & Facilitated Diffusion Active: Molecular & Bulk Slide 2 Membranes Slide 3 Fig. 6.2 (TEArt) Fatty acid Phosphorylated alcohol Polar (hydrophilic) region Nonpolar (hydrophobic) region Fatty acid GLYCEROLGLYCEROL Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Slide 4 Fig. 6.3 (TEArt) Polar hydrophilic heads Nonpolar hydrophobic tails Polar hydrophilic heads Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Slide 5 Outside Cell Cytoplasm (inside cell) Cholesterol Transmembrane proteins Peripheral protein Glycoprotein Carbohydrate Glycolipid Phospholipid Bilayer Fluid Mosaic Model of Cell Membrane Slide 6 6 Cell Membrane Structure 1. Phospholipid bilayer 2. Proteins 3. Carbohydrates Attached to lipids Glycolipids Attached to proteins Glycoproteins 4. Cholesterol Slide 7 Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme Cell surface identity marker Attachment to the cytoskeleton Cell adhesion Membrane Protein Functions Slide 8 Phospholipids Polar areas of protein Nonpolar areas of protein Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anchoring Proteins in the Phospholipid Bilayer Slide 9 1.Single-Pass Anchors 2.Multi-Pass Channels & Pores Carriers Structure of Membrane Proteins Slide 10 Examples of Single Pass Proteins Receptors, anchors & enzymes Anchors - Cell Surface Markers Self-recognition MHC Antigen Guanylyl cyclase Second messenger Protein anchor Protein receptor Protein enzyme Smooth muscle relaxation NO Nitric oxide substrate Unique part of protein cGMP degradation by phosphdiesterase V Slide 11 Fig. 6.12 (TEArt) Lump of sugar Sugar molecule Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Solute dissolves in a solvent. Solutes move from a high to a low concentration. Diffusion Slide 12 Fig. 6.14 (TEArt) Urea molecule Water molecules Osmosis is Water Diffusion Across a Semipermeable Membrane Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Slide 13 Shriveled cells Normal cells Cells swell and eventually burst Hyperosmotic solution Isoosmotic solution Hypoosmotic solution Direction of Water Diffusion Slide 14 Fig. 6.15c (TEArt) Plasmolysis Cell body shrinks from cell wall Normal turgid cell Turgor Pressure Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hyperosmotic External Solution Water Diffusion in Plant Cells Isoosmotic External Solution Hypoosmotic External Solution Slide 15 15 Maintaining Osmotic Balance Life in a osmotic environment 1. Extrusion e.g. Contractile Vacuoles in Paramecium 2. Isoosmotic solutions e.g. Blood Protein 3. Live with it e.g. Turgor pressure Slide 16 Moving Molecules into or out of Cells - Overview of Passive & Active Transport I. Passive Transport 1. Always down a concentration gradient 2. Always involves proteins called A. Channels B. Carriers C. Pores porins II. Active Transport 1. Always down a concentration gradient 2. Small molecules transported through A. Protein Pumps 3. Large molecules transported by vesicles A. Endocytosis B. Exocytosis Slide 17 1. Multi-pass proteins create openings in the membrane Moving Molecules into or out of Cells - Passive Transport Passive Transport 1. Channels 2. Carriers Solute molecule Transport protein Multi-Pass Protein Slide 18 Moving Molecules into or out of Cells - Passive Transport Example of a Channel Passive transport of 1) Water-soluble molecules 2) Ions Selectivity filter Inside cell Outside cell K + ion K + ion channel Side view Top view Slide 19 Moving Molecules into or out of Cells - Passive Transport Carriers & Facilitated Diffusion Passive transport of 1) ions 2) Sugars 3) amino acids Outside cell Inside cell Examples of Facilitated Diffusion in Red Blood Cells 1) Cl - and bicarbonate ions 2) Glucose carrier Slide 20 Pores & Porin Proteins Allow Water and Small Molecules into Cells Porins are transport channels 1.Allow movement of small molecules Water Ions Organic Wastes Porin Protein Pleated folds 2003 Nobel Prize in Chemistry Aquaporin Water Channels Slide 21 Major Sites of ExpressionComments Aquaporin-0Eye: lens fiber cellsFluid balance within the lens Aquaporin-1 Red blood cellsOsmotic protection Kidney: proximal tubuleConcentration of urine Eye: ciliary epitheliumProduction of aqueous humor Brain: choriod plexusProduction of cerebrospinal fluid Lung: alveolar epithelial cellsAlveolar hydration state Aquaporin-2Kidney: collecting ductsMediates antidiuretic hormone activity Aquaporin-3 * Kidney: collecting ductsReabsorbtion of water into blood Trachea: epithelial cellsSecretion of water into trachea Aquaporin-4 Kidney: collecting ductsReabsorbtion of water Brain: ependymal cellsCSF fluid balance Brain: hypothalamusOsmosensing function? Lung: bronchial epitheliumBronchial fluid secretion Aquaporin-5 Salivary glandsProduction of saliva Lacrimal glandsProduction of tears Aquaporins are Water Channels Slide 22 1. Proteins allow transport 2. Mechanisms of movement through proteins 1.Passive Transport Channels, carriers & pores Simple Diffusion Facilitated Diffusion 2.Active Transport Molecular Transport Bulk Transport Exocytosis Endocytosis How do molecules move across membranes? Slide 23 P P P A P P P A Na + Extracellular Intracellular ATP P P P A P P A P ADP 1. Protein in membrane binds intracellular sodium. 2. ATP phosphorylates protein with bound sodium. 3. Phosphorylation causes conformational change in protein, allowing sodium to leave. P P A P ADP 4. Extracellular potassium binds to exposed sites. K+K+ P P A P ADP+P i 5. Binding of potassium causes dephosphorylation of protein. 6. Dephosphorylation of protein triggers change back to original conformation, potassium moves into cell, and the cycle repeats. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Active Transport Sodium-Potassium Pump Slide 24 Fig. 6.19 (TEArt) Outside cell Inside cell Na + Coupled transport protein Sugar K+K+ Na/K pump Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Active Transport - Cotransport Slide 25 Example of Glucose Transport From Intestine to Blood Slide 26 Bulk Transport Across Membranes Exocytosis - discharge of material from vesicles at the cell surface Endocytosis - enveloping food phagocytosis - particulate material pinocytosis - liquid receptor-mediated - transport of specific molecules Slide 27 27 Bulk Tranport: Exocytosis Slide 28 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm Plasma membrane Bulk Transport: Endocytosis Slide 29 Fig. 6.16c (TEArt) Coated pit Target molecule Receptor protein Coated Vesicle Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Carrier-Mediated Endocytosis Slide 30 Example of Neurotransmitter Movement from Cell to Cell Reuptake transporter Slide 31 END Membranes & Transport

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