Outline - Membranes. Membranes. Plasma Membrane Properties and Structure. Properties: No Free Ends Internal space

Transcription

1 Outline - Membranes 1. Fluid Mosaic Model of Membrane Structure 2. Membrane Proteins 1. Kinds of membrane s 2. Membrane structure 3. Transport Mechanisms Passive: Diffusion & Facilitated Diffusion Active: Molecular & Bulk Plasma Membrane Properties and Structure Properties: No Free Ends Internal space Fluid Mosaic Model of Membrane Structure Fluid = Phospholipid bilayer Mosaic = Embedded Proteins: Transport s: channels and carriers Receptor Proteins: gates, triggers Recognition Proteins: ID Tags Plasma Membrane Function Membranes Gate Keeper Regulation Communication Transport Selectively permeable Elastic Protection 1

2 Polar hydrophilic heads Glyco Fluid Mosaic Model of Cell Membrane Outside Cell Carbohydrate Phospholipid Bilayer Glycolipid Nonpolar hydrophobic tails Polar hydrophilic heads Peripheral Cholesterol Cytoplasm (inside cell) Transmembrane s Cell Membrane Structure Summary 1. Phospholipid bilayer 2. Proteins Transmembrane Interior Outside Plasma membrane Inside Six Functions of Membrane Proteins Transporter Enzyme Cell surface receptor 3. Carbohydrates Attached to lipids Glycolipids Attached to s Glycos 4. Cholesterol Cell surface identity marker Cell adhesion Attachment to the cytoskeleton 7 2

3 Anchoring Proteins in the Phospholipid Bilayer Nonpolar areas of Phospholipids Polar areas of Types of Transport Passive Transport Follows concentration gradient Does not require energy Direct or via channels Examples: Diffusion, Facilitated Diffusion and Osmosis Active Transport: Against concentration gradient Requires energy Bulk Transport Exocytosis and Endocytosis - Overview of Types of Transport I. Passive Transport 1. Always down a concentration gradient 2. Always involves s called A. Channels B. Carriers C. Pores porins II. Active Transport 1. Always up a concentration gradient 2. Small molecules transported through A. Protein Pumps 3. Large molecules transported by vesicles A. Endocytosis B. Exocytosis Fig (TEArt) Diffusion Solute dissolves in a solvent. Lump of Solutes sugar move from a high to a low concentration. Sugar molecule 3

4 Fig (TEArt) Osmosis is Water Diffusion Across a Semipermeable Membrane Direction of Water Diffusion External environment of a cell can vary Hypertonic Isotonic Hypotonic solution solution solution Water diffuses out Water diffuses out Water diffuses in and in = equilibrium Solute molecule Water molecules Shriveled cells Normal cells Cells swell & burst Fig. 6.15c (TEArt) Water Diffusion in Plant Cells Hypertonic External Solution Isotonic External Solution Hypotonic External Solution Maintaining Osmotic Balance Life in a osmotic environment 1. Extrusion e.g. Contractile Vacuoles in Paramecium Plasmolysis Cell body shrinks from cell wall Normal cell Turgor Pressure 2. Isotonic solutions e.g. Blood Protein 3. Live with it e.g. Turgor pressure 4

5 Passive Transport 1. Multi-pass s create openings in the membrane - Passive Transport Channels K + ion channel Passive Transport 1. Channels 2. Carriers 3. Pores Solute molecule Selectivity filter Outside cell Multi-Pass Protein Side view Top view Transport Passive transport of 1) Water-soluble molecules 2) Ions Inside cell K + ion Outside cell Passive Transport Carriers Passive transport of 1) ions 2) Sugars 3) amino acids Passive Transport Pores Facilitated Diffusion in Red Blood Cells 1) Cl - and bicarbonate ions Porin Protein 2) Glucose carrier Pleated folds Porins are transport channels 1.Allow movement of small molecules Water Ions Organic Wastes 2003 Nobel Prize in Chemistry Aquaporin Water Channels Inside cell 5

6 Example: Active Transport Sodium-Potassium Pump Extracellular Na + P ATP PPA Intracellular 1. Protein in membrane binds intracellular sodium. K + P PPA ATP 2. ATP phosphorylates with bound sodium. P P PA ADP 3. Phosphorylation causes conformational change in, allowing sodium to leave. Fig (TEArt) Active Transport - Cotransport Outside cell Na/K pump Na + Coupled transport Sugar P P PA ADP 4. Extracellular potassium binds to exposed sites. Animation P P PA ADP+P i 5. Binding of potassium causes dephosphorylation of. P PPA ATP 6. Dephosphorylation of triggers change back to original conformation, potassium moves into cell, and the cycle repeats. K + Inside cell Animation Bulk Transport Across Membranes Exocytosis - discharge of material from vesicles at the cell surface Bulk Tranport: Exocytosis Endocytosis - enveloping food phagocytosis - particulate material pinocytosis - liquid receptor-mediated - transport specific molecules Animation 24 6

7 Bulk Transport: Endocytosis Carrier-Mediated Endocytosis Coated pit Plasma membrane Clathrin Receptor Coated vesicle Cytoplasm END Membranes & Transport 7