Metabolism and Energy Mrs. Stahl AP Biology. The Energy of Life The living cell is a miniature chemical factory where thousands of reactions occur The.

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Metabolism and EnergyMrs. StahlAP BiologyThe Energy of LifeThe living cell is a miniature chemical factory where thousands of reactions occurThe cell extracts energy stored in sugars and other fuels and applies energy to perform workSome organisms even convert energy to light, as in bioluminescence2Figure 8.1

Figure 8.1 What causes these breaking waves to glow?3Forms of EnergyEnergy is the capacity to cause changeEnergy exists in various forms, some of which can perform work Kinetic energy is energy associated with motionHeat (thermal energy) is kinetic energy associated with random movement of atomsor moleculesPotential energy is energy that matter possesses because of its location or structureChemical energy is potential energy availablefor release in a chemical reactionEnergy can be converted from one form to another

Figure 8.2A diver has more potentialenergy on the platformthan in the water.Diving convertspotential energy tokinetic energy.A diver has less potentialenergy in the waterthan on the platform.Climbing up converts the kineticenergy of muscle movementto potential energy.Figure 8.2 Transformations between potential and kinetic energy6The Laws of Energy TransformationThermodynamics is the study of energy transformationsAn isolated system, such as that approximated by liquid in a thermos, is unable to exchange energy or matter with its surroundingsIn an open system, energy and matter canbe transferred between the system and its surroundingsOrganisms are open systemsThe First Law of ThermodynamicsAccording to the first law of thermodynamics, the energy of the universe is constantEnergy can be transferred and transformed,but it cannot be created or destroyedThe first law is also called the principle of conservation of energyPlants do not produce energy, they transform light energy to chemical energy. During every transfer, some energy is converted to heat -> a system can use heat to do work only when there is a difference that results in heat flowing from warmer locations to cooler ones. If heat is uniform as in a living cell, heat can only be used to warm the organism.

Figure 8.3(a)(b)First law of thermo-dynamicsSecond law of thermodynamicsChemicalenergyHeatCO2H2OFigure 8.3 The two laws of thermodynamics10The Second Law of ThermodynamicsDuring every energy transfer or transformation, some energy is unusable, and is often lost as heatAccording to the second law of thermodynamicsEvery energy transfer or transformation increases the entropy (disorder) of the universeEntropy- measure of disorder or randomnessIncrease entropy = increase heat Living cells unavoidably convert organizedforms of energy to heatSpontaneous processes occur without energy input; they can happen quickly or slowly.Living systems create ordered structures from less ordered starting materials.Ex- amino acids are ordered into polypeptide chainsEx- structure of a multicellular body is organized and complex.For a process to occur without energy input, it must increase the entropy of the universeHighly Ordered Living Organisms Do Not Violate the Second Law of ThermodynamicsOrganisms also take in organized forms of matter and energy from its surrounding and replaces them with less ordered forms. Ex- animal consumes organic molecules as food and catabolizes (breaks down -> metabolism) them to low energy molecules such as carbon dioxide and water. The evolution of more complex organisms does not violate the second law of thermodynamics because Earth and organisms are open systems. We get our energy from the sun and we can evolve and create order by increasing the disorder of the universe.Entropy (disorder) may decrease in an organism, but the universes total entropy increases

The free-energy change of a reaction tells us whether or not the reaction occurs spontaneouslyBiologists want to know which reactions occur spontaneously and which require input of energyTo do so, they need to determine energy changes that occur in chemical reactionsFree-Energy Change, GA living systems free energy is energy that can do work when temperature and pressure are uniform, as in a living cell The change in free energy (G) during a process is related to the change in enthalpy, or change in total energy (H), change in entropy (S), and temperature in Kelvin units (T) G = H - TSH= enthalpy, in a spontaneous reaction it gets smaller or decreases because energy is released.S= entropy, measure of the disorder . In a spontaneous reaction entropy increases.T= temperature, when temperature increases the spontaneous reaction is more likely to happen.What makes G decrease?A decrease in HAn increase in SAn increase in TOnly processes with a negative G are spontaneous also known as exergonic ( releases free energy as heat)

G > 0 = endergonic reaction, energy must be addedG = 0 = equilibriumIncreases in temperature amplify the entropy. Think about a cherry bomb-> add heat and it blows up.Not all the energy in a system is available for work because the entropy component must be subtracted from the enthalpy component. What remains is the free energy, referred to as the stability of the system.

Figure 8.5b(a) Gravitational motion(b) Diffusion(c) Chemical reactionFigure 8.5b The relationship of free energy to stability, work capacity, and spontaneous change (part 2: examples)19Exergonic and Endergonic Reactions in MetabolismExergonic Reaction: G is negative, SpontaneousThe products of the reaction contain less free energy than reactants. Bond is lower or disorder is higher or both.Energy is released. Ex- Cellular RespirationEndergonic reaction: absorbs free energy from its surroundings and is non-spontaneousEnergy must be supplied, ex- photosynthesis

Exergonic reaction: energy released,spontaneousEndergonic reaction: energy required,nonspontaneous(a)(b)Free energyFree energyReactantsReactantsEnergyEnergyProductsProductsAmount ofenergyreleased(G < 0)Amount ofenergyrequired(G > 0)Progress of the reactionProgress of the reactionFigure 8.6 Free energy changes (G) in exergonic and endergonic reactions21If all chemical reactions that release free energy tend to occur spontaneously, why havent all such reactions already occurred?Most reactions require an input of energy to get started such as endergonic reactions (photosynthesis). Activation EnergyBefore any bonds can form, they have to be broken by energy input.Defined as the extra energy needed to destabilize existing chemical bonds and initiate / start a chemical reaction.Exergonic rate depends on the activation energy required for the reaction to begin.Rates of reactions are increased by:Increasing the energy of reacting moleculesLowering activation energyCatalysis / CatalystsA substance that lowers the activation energyEx- enzymesThey cannot make an endergonic reaction proceed spontaneously.Adenosine Triphosphate- ATPMain energy currency in all living cells1. Makes sugars2. Supplying activation energy for chemical reactions3. Actively transporting substances across membranes4. Moving through the environment and growing

The Structure and Hydrolysis of ATPATP (adenosine triphosphate) is the cells energy shuttleATP is composed of ribose (a sugar), adenine(a nitrogenous base), and three phosphate groupsHow does ATP store energy?The energy is stored in the bonds between the triphosphates. These groups repel each other due to their negative charges, and the covalent bonds joining the phosphates are unstable and can break. They are easily broken by hydrolysis and when they break they release and transfer a large amount of energy which can be used.

Figure 8.9a(a) The structure of ATPRiboseAdenineTriphosphate group(3 phosphate groups)Figure 8.9a The structure and hydrolysis of adenosine triphosphate (ATP) (part 1: structure)28

Figure 8.9b(b) The hydrolysis of ATPAdenosine triphosphate (ATP)Adenosine diphosphate(ADP)EnergyInorganicphosphateH2OFigure 8.9b The structure and hydrolysis of adenosine triphosphate (ATP) (part 2: hydrolysis)29How does ATP become ADP?The bonds are broken on the third phosphate, releasing energy. ATP -> ADP +PiEnergy = 7.3kcal / molThis release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves

Why does the hydrolysis of ATP yield so much energy?The release of energy initially comes from the chemical change to a state of lower free energy.Each phosphate group has a negative charge. Three like charges are crowded together and their mutual repulsion contributes to the instability of the molecule. How the Hydrolysis of ATP Performs WorkThe three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATPIn the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reactionOverall, the coupled reactions are exergonic ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactantThe recipient molecule is now called a phosphorylated intermediate Transport and mechanical work in the cell are also powered by ATP hydrolysisATP hydrolysis leads to a change in protein shape and binding ability

Figure 8.11Transport proteinSoluteSolute transported(a) Transport work: ATP phosphorylates transport proteins.Mechanical work: ATP binds noncovalently to motorproteins and then is hydrolyzed.Protein and vesicle movedMotor proteinCytoskeletal trackATPATPADPPiADPPiPiPATP(b)VesicleFigure 8.11 How ATP drives transport and mechanical work35What reactions does ATP Drive?Endergonic Reactions

Figure 8.12Energy fromcatabolism(exergonic, energy-releasing processes)Energy for cellularwork (endergonicenergy-consumingprocesses)ADPPiH2OATPFigure 8.12 The ATP cycle37The 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 cellThe ATP cycle is a revolving door through which energy passes during its transfer from catabolic to anabolic pathwaysEnzymes speed up metabolic reactions by lowering energy barriersA catalyst is a chemical agent that speeds up a reaction without being consumed by the reactionSubstrate- The molecules that will undergo the reactionAn enzyme is a catalytic proteinHydrolysis of sucrose by the enzyme sucrase isan example of an enzyme-catalyzed reaction

Figure 8.UN02Sucrose(C12H22O11)Glucose(C6H12O6)Fructose(C6H12O6)SucraseFigure 8.UN02 In-text figure, sucrose hydrolysis, p.15140Functions of Enzymes1. Lowers the activation energy required for new bonds to form2. Speeds up the rate of reaction3. Regulates metabolic pathwaysWhat is the importance of carbonic acid in vertebrate red blood cells?Vertebrate RBCs have an enzyme called carbonic anhydrase, which aids in breaking down carbon dioxide in our blood. 600,000 molecules of carbonic acid form every second. This enzyme increases the rate of reaction one million times. The Active SiteThey are pockets on the enzyme where the substrates fit perfectly.Catalysis in the Enzymes Active SiteIn an enzymatic reaction, the substrate binds to the active site of the enzymeThe active site can lower an EA barrier byOrienting substrates correctlyStraining substrate bondsProviding a favorable microenvironmentCovalently bonding to the substrateEnzyme Substrate ComplexA substrate molecule binds with an enzyme at its active site. Chemical reactions occur and bonds are either broken or new ones are formed. The substrates have been changed into products. The products leave the enzyme and the process starts all over again. Induced FitWhen the active site changes its shape slightly so that it can bind onto the substrate more tightly.

Figure 8.15SubstrateActive siteEnzymeEnzyme-substratecomplexFigure 8.15 Induced fit between an enzyme and its substrate47Where are most enzymes found?CytoplasmCell membranesOrganellesMultienzyme Complexes and AdvantagesThey allow a plethora of chemical reactions to occur-> molecular machineAdvantages:1. All reactions can be controlled as a unit2. No unwanted side reactions3. Rate of the enzyme is limitedThe Activation Energy BarrierEvery chemical reaction between molecules involves bond breaking and bond formingThe initial energy needed to start a chemical reaction is called the free energy of activation,or activation energy (EA) Activation energy is often supplied in the form of thermal energy that the reactant molecules absorb from their surroundings

Figure 8.13Transition stateReactantsProductsProgress of the reactionEAG < OFree energyABDCABDCABDCFigure 8.13 Energy profile of an exergonic reaction51Animation: How Enzymes Work

Figure 8.16-1Substrates enteractive site.SubstratesSubstrates areheld in activesite by weakinteractions.12Enzyme-substratecomplexFigure 8.16-1 The active site and catalytic cycle of an enzyme (step 1)53

Figure 8.16-2Substrates enteractive site.SubstratesSubstrates areconverted toproducts.Substrates areheld in activesite by weakinteractions.12Enzyme-substratecomplex3Figure 8.16-2 The active site and catalytic cycle of an enzyme (step 2)54

Figure 8.16-3Substrates enteractive site.SubstratesSubstrates areconverted toproducts.Substrates areheld in activesite by weakinteractions.12Products arereleased.Enzyme-substratecomplexProducts43Figure 8.16-3 The active site and catalytic cycle of an enzyme (step 3)55

Figure 8.16-4Substrates enteractive site.SubstratesSubstrates areconverted toproducts.Substrates areheld in activesite by weakinteractions.12Products arereleased.EnzymeEnzyme-substratecomplexActive siteis availablefor newsubstrates.Products543Figure 8.16-4 The active site and catalytic cycle of an enzyme (step 4)56Effects of Local Conditions on Enzyme ActivityAn enzymes activity can be affected byGeneral environmental factors, such as temperature and pHChemicals that specifically influence the enzymeEffects of Temperature and pHEach enzyme has an optimal temperature in which it can functionEach enzyme has an optimal pH in which it can functionOptimal conditions favor the most active shape for the enzyme moleculeTemperatureAbove the optimal temperature= forces are too weak to maintain the enzymes shape -> denaturesBelow optimum temperatures= hydrogen bonds and hydrophobic interactions that determine the enzymes shape is not flexible to allow induced fit.Humans= 35 to 40 CelciusProkaryotes= 70 Celcius (hot springs)pHInteractions are sensitive to the hydrogen ion concentration of the fluid in which the enzyme is dissolved, changing the concentration. Shifts the balance between +/- amino acidsOptimum pH= 6 to 8

Figure 8.17Optimal temperature fortypical human enzyme(37C)Optimal pH for pepsin(stomachenzyme)Optimal pH for trypsin(intestinalenzyme)Optimal temperature forenzyme of thermophilic(heat-tolerant)bacteria (77C)Temperature (C)pH012345678910020406080100120(a) Optimal temperature for two enzymes(b) Optimal pH for two enzymesRate of reactionRate of reactionFigure 8.17 Environmental factors affecting enzyme activity61Enzyme Inhibitors- substance that binds to an enzyme and decreases its activityCompetitive inhibitors bind to the active siteof an enzyme, competing with the substrateNoncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective. Binds at the allosteric site.Examples of inhibitors include toxins, poisons, pesticides, and antibiotics

Figure 8.18(a) Normal binding(b) Competitive inhibition(c)NoncompetitiveinhibitionSubstrateActive siteEnzymeCompetitiveinhibitorNoncompetitiveinhibitorFigure 8.18 Inhibition of enzyme activity63Allosteric enzymes- enzymes that exist as either active or inactiveAllosteric site- on /off chemical switchesAllosteric inhibitors- binds to the allosteric site and reduces enzyme activityAllosteric Activator- keeps the enzyme active , increases enzyme activityCofactorsCofactors are non-protein enzyme helpers that are found around the active site to assist in catalysis. They help weaken bonds and make them easier to break.Cofactors may be inorganic (such as a metal in ionic form) or organicAn organic cofactor is called a coenzymeCoenzymes serve as an electron acceptor which then transfers the electrons to a different enzyme, which releases them to the substrates in another reaction (Ex- NADP)The Evolution of EnzymesEnzymes are proteins encoded by genesChanges (mutations) in genes lead to changesin amino acid composition of an enzymeAltered amino acids in enzymes may result in novel enzyme activity or altered substrate specificityUnder new environmental conditions a novelform of an enzyme might be favoredFor example, six amino acid changes improved substrate binding and breakdown in E. coli Regulation of enzyme activity helps control metabolismChemical chaos would result if a cells metabolic pathways were not tightly regulatedA cell does this by switching on or off the genes that encode specific enzymes or by regulating the activity of enzymesLocalization of Enzymes Within the CellStructures within the cell help bring order to metabolic pathwaysSome enzymes act as structural componentsof membranesIn eukaryotic cells, some enzymes reside in specific organelles; for example, enzymes for cellular respiration are located in mitochondriaMetabolismTotality of an organisms chemical reaction. Emergent property of life that arises from interactions between molecules within the orderly environment of the cell. Catabolic pathways release energy by breaking down complex molecules into simpler compoundsCellular respiration, the breakdown of glucosein the presence of oxygen, is an example of a pathway of catabolism Anabolic pathways consume energy to build complex molecules from simpler onesThe synthesis of protein from amino acids is an example of anabolismBioenergetics is the study of how energy flows through living organismsBiochemical PathwaysOrganizational units of metabolism. The elements an organism needs / controls to achieve metabolic activity.They think they came from early oceans, creating an organic soup.Feedback InhibitionIn feedback inhibition, the end product of a metabolic pathway shuts down the pathwayFeedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is neededCells! Cells are not in equilibrium; they are open systems experiencing a constant flow of materialsA defining feature of life is that metabolism is never at equilibriumA catabolic pathway in a cell releases free energy in a series of reactions