Forms of EnergyATP powers cellular work by coupling exergonic reactions to endergonic reactionsSlide 3Slide 4Enzymes speed up metabolic reactions by lowering energy barriersSlide 6Enzymes Lower the EA BarrierSlide 8Substrate Specificity of EnzymesSlide 10Slide 11Plasma membraneSlide 13Passive transport is diffusion of a substance across a membrane with no energy investmentSlide 15Effects of Osmosis on Water BalanceSlide 17Water Balance of Cells Without WallsSlide 19Water Balance of Cells with WallsActive transport uses energy to move solutes against their gradientsSlide 22Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosisSlide 24The Three Stages of Cell SignalingSlide 26Forms of Energy•Energy is the capacity to cause change. It exists in various forms.•Kinetic energy is energy associated with motion.•Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules•Potential energy is energy that matter possesses because of its location or structure•Chemical energy is potential energy available for release in a chemical reaction•Energy can be converted from one form to another •Thermodynamics is the study of energy transformationsATP powers cellular work by coupling exergonic reactions to endergonic reactions•ATP (adenosine triphosphate) is the cell’s energy shuttle•The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis•Energy is released from ATP when the terminal phosphate bond is brokenFig. 8-8Phosphate groupsRiboseAdenineATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groupsFig. 8-12PiADP+Energy fromcatabolism (exergonic,energy-releasingprocesses)Energy for cellularwork (endergonic,energy-consumingprocesses)ATP+H2OThe Regeneration of ATPATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP)The energy to phosphorylate ADP comes from catabolic reactions in the cellEnzymes speed up metabolic reactions by lowering energy barriers•A enzyme is a catalyst that speeds up a reaction without being consumed by the reaction•Every chemical reaction between molecules involves bond breaking and bond forming•The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (EA) •For a reaction to happen the reactants must overcome the EA barrier.•Activation energy is often supplied in the form of heat from the surroundingsFig. 8-14Progress of the reactionProductsReactants∆G < OTransition stateFree energyEADCBADDCCBBAAEnzymes Lower the EA Barrier•Enzymes catalyze reactions by lowering the EA barrier•Enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually•The reactant that an enzyme acts on is called the enzyme’s substrate •The enzyme binds to its substrate, forming an enzyme-substrate complex•The active site is the region on the enzyme where the substrate bindsFig. 8-15Progress of the reactionProductsReactants∆G is unaffectedby enzymeCourse ofreactionwithoutenzymeFree energyEAwithoutenzymeEA withenzymeis lowerCourse ofreactionwith enzymeFig. 8-16SubstrateActive siteEnzymeEnzyme-substratecomplex(b)(a)Substrate Specificity of Enzymes•Competitive inhibitors bind to the active site of an enzyme, competing with the substrate•Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective•Examples of inhibitors include toxins, poisons, pesticides, and antibioticsEnzyme InhibitorsFig. 8-19(a) Normal binding(c) Noncompetitive inhibition(b) Competitive inhibitionNoncompetitive inhibitorActive siteCompetitive inhibitorSubstrateEnzymeHydrophilicheadWATERHydrophobictailWATER•The plasma membrane is the boundary that separates the living cell from its surroundings•The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than othersPlasma membraneFig. 7-7Fibers ofextracellularmatrix (ECM)Glyco-proteinMicrofilamentsof cytoskeletonCholesterolPeripheralproteinsIntegralproteinCYTOPLASMIC SIDEOF MEMBRANEGlycolipidEXTRACELLULARSIDE OFMEMBRANECarbohydratePassive transport is diffusion of a substance across a membrane with no energy investment•Diffusion is the tendency for molecules to spread out evenly into the available space•Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movement in one direction•Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another.•The diffusion of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happenFig. 7-11Molecules of dyeMembrane (cross section)WATERNet diffusionNet diffusionEquilibrium(a) Diffusion of one soluteNet diffusionNet diffusionNet diffusionNet diffusionEquilibriumEquilibrium(b) Diffusion of two solutesAt dynamic equilibrium, as many molecules cross one way as cross in the other directionEffects of Osmosis on Water Balance•Osmosis is the diffusion of water across a selectively permeable membrane•Water diffuses across a membrane from the region of higher water concentration to the region of lower water concentration.(like the case with diffusion) Another way of saying that would be•Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentrationLowerconcentrationof solute (sugar)Fig. 7-12H2OHigher concentrationof sugarSelectivelypermeablemembraneSame concentrationof sugarOsmosisWater Balance of Cells Without Walls•Tonicity is the ability of a solution to cause a cell to gain or lose water•Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane•Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water•Hypotonic solution: Solute concentration is less than that inside the cell; cell gains waterFig. 7-13Hypotonic solution(a) Animal cell(b) Plant cellH2OLysedH2OTurgid (normal)H2OH2OH2OH2ONormalIsotonic solutionFlaccidH2OH2OShriveledPlasmolyzedHypertonic solutionWater Balance of Cells with Walls•Cell walls help maintain water balance•A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid