Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOverview: The Energy of Life• The living cell is a miniature chemical factorywhere thousands of reactions occur• The cell extracts energy and applies energy toperform work• Some organisms even convert energy to light, asin bioluminescenceCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 8.1: An organism’s metabolism transforms matterand energy, subject to the laws of thermodynamics• Metabolism is the totality of an organism’schemical reactions• Metabolism is an emergent property of life thatarises from interactions between molecules withinthe cellCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOrganization of the Chemistry of Life intoMetabolic Pathways• A metabolic pathway begins with a specificmolecule and ends with a product• Each step is catalyzed by a specific enzymeLE 8-UN141Enzyme 1A BReaction 1Enzyme 2CReaction 2Enzyme 3DReaction 3ProductStartingmoleculeCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Catabolic pathways release energy by breakingdown complex molecules into simpler compounds• Anabolic pathways consume energy to buildcomplex molecules from simpler ones• Bioenergetics is the study of how organismsmanage their energy resourcesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsForms of Energy• Energy is the capacity to cause change• Energy exists in various forms, some of which canperform workCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Kinetic energy is energy associated with motion– Heat (thermal energy) is kinetic energy associatedwith random movement of atoms or molecules• Potential energy is energy that matter possessesbecause of its location or structure– Chemical energy is potential energy available forrelease in a chemical reaction• Energy can be converted from one form to anotherAnimation: Energy ConceptsAnimation: Energy ConceptsLE 8-2On the platform,the diver hasmore potentialenergy.Diving convertspotentialenergy to kinetic energy.Climbing up convertskinetic energy ofmuscle movement topotential energy.In the water, the diver has lesspotential energy.Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Laws of Energy Transformation• Thermodynamics is the study of energytransformations• A closed system, such as that approximated byliquid in a thermos, is isolated from itssurroundings• In an open system, energy and matter can betransferred between the system and itssurroundings• Organisms are open systemsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe First Law of Thermodynamics• According to the first law of thermodynamics, theenergy of the universe is constant– Energy can be transferred and transformed– Energy cannot be created or destroyed• The first law is also called the principle ofconservation of energyCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Second Law of Thermodynamics• During every energy transfer or transformation,some energy is unusable, often lost as heat• According to the second law of thermodynamics,every energy transfer or transformation increasesthe entropy (disorder) of the universeLE 8-3Chemical energyHeatCO2First law of thermodynamics Second law of thermodynamicsH2OCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Living cells unavoidably convert organized formsof energy to heat• Spontaneous processes occur without energyinput; they can happen quickly or slowly• For a process to occur without energy input, itmust increase the entropy of the universeCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsBiological Order and Disorder• Cells create ordered structures from less orderedmaterials• Organisms also replace ordered forms of matterand energy with less ordered forms• The evolution of more complex organisms doesnot violate the second law of thermodynamics• Entropy (disorder) may decrease in an organism,but the universe’s total entropy increasesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 8.2: The free-energy change of a reaction tellsus whether the reaction occurs spontaneously• Biologists want to know which reactions occurspontaneously and which require input of energy• To do so, they need to determine energy changesthat occur in chemical reactionsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• The change in free energy (∆G) during a processis related to the change in enthalpy, or change intotal energy (∆H), and change in entropy (T∆S): ∆G = ∆H - T∆S• Only processes with a negative ∆G arespontaneous• Spontaneous processes can be harnessed toperform workCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsFree Energy, Stability, and Equilibrium• Free energy is a measure of a system’s instability,its tendency to change to a more stable state• During a spontaneous change, free energydecreases and the stability of a system increases• Equilibrium is a state of maximum stability• A process is spontaneous and can perform workonly when it is moving toward equilibriumLE 8-5Gravitational motion Diffusion Chemical reactionCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsFree Energy and Metabolism• The concept of free energy can be applied to thechemistry of life’s processesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsExergonic and Endergonic Reactions in Metabolism• An exergonic reaction proceeds with a net releaseof free energy and is spontaneous• An endergonic reaction absorbs free energy fromits surroundings and is nonspontaneousLE 8-6aReactantsEnergyProductsProgress of the reactionAmount ofenergyreleased(ΔG < 0)Free energyExergonic reaction: energy releasedLE 8-6bReactantsEnergyProductsProgress of the reactionAmount ofenergyrequired(ΔG > 0)Free energyEndergonic reaction: energy requiredCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsEquilibrium and Metabolism• Reactions in a closed system eventually reachequilibrium and then do no work• Cells are not in equilibrium; they are open systemsexperiencing a constant flow of materials• A catabolic pathway