The Cell Membrane 1 Movement of molecules and ions across the cell membrane Diffusion osmosis tonicity 2 The phospholipid bilayer is a dynamic structure The movement and fluidity of the bilayer is affected by temperature and the composition of the membrane 3 How do molecules move across the membrane Solvent the substance in which the solute dissolves it is usually found in a larger quantity Solute the component in a solution which changes state upon dissolving it is found in a smaller quantity Concentration gradient the difference in solute concentration between two areas 4 Diffusion Diffusion spontaneous movement of molecules from an area of high concentration to low concentration i e down a concentration 5 gradient Osmosis 6 7 Effect of tonicity on the cell 8 9 Plant Cells Prefer to Live in a Hypotonic Environment 10 Osmosis Is the diffusion of water across a selectively permeable membrane from a region of high water concentration low solute concentration to a region of low water concentration high solute concentration 11 Some important terms Hypotonic In comparing two solutions referring to the one with the lower solute concentration thus higher water concentration Hypertonic In comparing two solutions referring to the one with the higher solute concentration thus lower water concentration Isotonic Having the same solute concentration thus same water concentration as another solution 12 Membrane proteins and the fluid mosaic model 13 14 15 The role of proteins in the movement of ions and other molecules Facilitated diffusion 16 How do membrane proteins affect ions and molecules Researchers have identified three broad groups of transmembrane proteins Channel proteins Transporters pumps 17 Let s see again what happens to ions in the membrane bilayer 18 Membrane channel protein are highly selective and highly regulated 19 Membrane channel protein are highly selective and highly regulated second example 20 Passive and facilitated diffusion Passive transport is produced by diffusion along an electrochemical gradient doesn t require an expenditure of energy Facilitated diffusion is the passive transport of substances that otherwise would cross a membrane 21 Carrier Proteins 22 Active Transport The movement of substance across a cell membrane against the concentration of an electrochemical gradient with an expenditure of energy ATP specific transport molecules 23 Active Transport 24 Cotransport 25 Active Transport and Pumps 5 Unbound protein 6 Potassium binding 7 Shape change 8 Release The movement of substance across a cell membrane against the concentration of an electrochemical gradient with an expenditure of energy ATP specific transport molecules 26 Summary of Mechanisms of membrane transport 27
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