Slide 1Amphipathic lipidsHow Amphipathic molecules behave in waterLet’s go back to the properties of waterNon-polar compounds do not interact with water moleculesHydrocarbon are unstable in waterSlide 7LiposomesPlanar artificial bilayersWhat substances cross the lipid bilayer?PermeabilityHow fast can some molecules cross the membrane?How fast can some molecules cross the membrane?Slide 14Type of Hydrocarbon TailsSlide 16Length of the hydrocarbon tails.Slide 18Amount of CholesterolSlide 20Slide 21The phospholipid bilayer is a dynamic structureHow do molecules move across the membrane?DiffusionOsmosisSlide 26Effect of tonicity on the cellSlide 28Plant Cells Prefer to Live in a Hypotonic EnvironmentOsmosisSome important termsMembrane proteins and the fluid mosaic modelSlide 33Slide 34Slide 35How do membrane proteins affect ions and molecules?Let’s see again what happens to ions in the membrane bilayerSlide 38Slide 39Passive and facilitated diffusionCarrier ProteinsActive TransportActive Transport and PumpsSummary of Mechanisms of membrane transportSlide 45Slide 46Slide 48The Cell MembraneAmphipathic lipidsHow Amphipathic molecules behave in waterThey are tiny dropletsof phospholipids thatform when the hydrophilicRegions face water andthe hydrophobic tail are force together.Lipid bilayers arecreated when twosheets of phospholipids molecules alignLet’s go back to the properties of waterNon-polar compounds do not interact with water molecules•Non-polar compounds don’t dissolve in water.•They interact with each other.•They are called hydrophobic compounds.Octane interacts withitself, but not with waterHydrocarbon are unstable in waterBecause they disrupt the hydrogen bonding betweenthe water molecules.Van der Waals interactions keep the hydrophobic region in the lipid bilayer stableLiposomesPlanar artificial bilayersWhat substances cross the lipid bilayer?Permeability•the tendency of a structure to allow a given substance to pass across.•Why is permeability important?–Certain molecules or ions can pass through a lipid bilayer more readily than others –The internal environment of the vesicle can become different from the outside.How fast can some molecules cross the membrane?Large molecules and charged molecules can’t pass through thenonpolar hydrophobic tails of the lipid bilayer.How fast can some molecules cross the membrane?Large molecules and charged molecules can’t pass through thenonpolar hydrophobic tails of the lipid bilayer.What characteristics of phospholipids affect the permeability of the cell membrane?•Type of hydrocarbons–Saturated–Unsaturated–Poly-unsaturated•The length of the hydrocarbon chain•Amount of cholesterol molecules in the membraneType of Hydrocarbon TailsIn a lipid bilayer membrane with unsaturated phospholipids, the hydrophobic part is less tightLength of the hydrocarbon tails.•Hydrophobic interactions become stronger as saturated hydrocarbon tails increase in length.•Membranes composed of phospholipids with long saturated tails are more stiff and less permeable.Fluidity of the lipids depends on the characteristics of their hydrocarbon chains.Amount of CholesterolMovement of molecules and ions across the cell membraneDiffusion, osmosis, tonicity.The phospholipid bilayer is a dynamic structure•The movement and fluidity of the bilayer is affected by temperature and the composition of the membrane.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 areasDiffusionDiffusion- spontaneous movement of molecules from an area of high concentration to low concentration (i.e., down a concentration gradient).OsmosisEffect of tonicity on the cellPlant Cells Prefer to Live in a Hypotonic EnvironmentOsmosis•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).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.Membrane proteins and the fluid mosaic modelThe role of proteins in the movement of ions and other molecules.Facilitated diffusionHow do membrane proteins affect ions and molecules?•Researchers have identified three broad groups of transmembrane proteins.–Channel proteins–Transporters –pumpsLet’s see again what happens to ions in the membrane bilayerMembrane channel protein are highly selective and highly regulatedMembrane channel protein are highly selective and highly regulated. (second example)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.Carrier ProteinsActive Transport•The movement of substance across a cell membrane against the concentration of an electrochemical gradient.–with an expenditure of energy (ATP)–specific transport molecules5. Unbound protein6. Potassium binding7. Shape change8. ReleaseActive Transport and Pumps•The movement of substance across a cell membrane against the concentration of an electrochemical gradient.–with an expenditure of energy (ATP)–specific transport moleculesSummary of Mechanisms of membrane transportWalter Dean Jennings IIIAt the State University of New York in March of 2003, Walter Dean Jennings III was pledging Psi Epsilon Chi. Jennings was involved in a hazing ritual that lasted ten days and included drinking numerous pitchers of water–sometimes through a funnel and often to the point of vomiting. Eventually, Jennings was forced to drink so much water that his brain swelled, and he died from water intoxication. 21 students were punished by the university over Jennings’ death and 13 were charged with, and plead guilty to, crimes that included criminally negligent homicide.•Talk to