Bài giảng Biology - Chapter 6: Metabolism: Energy and Enzymes

Metabolism: Energy and EnzymesChapter 62Flow of EnergyEnergy: the capacity to do work -kinetic energy: the energy of motion -potential energy: stored energyEnergy can take many forms: mechanical electric current heat light3Flow of EnergyMost forms of energy can be converted to heat energy.Heat energy is measured in kilocalories.One calorie = the amount of heat required to raise the temp of water by 1oC1 kilocalorie (kcal) = 1000 calories4Flow of EnergyPotential energy stored in chemical bonds can be transferred from one molecule to another by way of electrons.oxidation: loss of electronsreduction: gain of electronsredox reactions are coupled to each other.56Laws of ThermodynamicsFirst Law of Thermodynamics – energy cannot be created or destroyed -energy can only be converted from one form to anotherFor example:sunlight energy chemical energy photosynthesis7Laws of ThermodynamicsSecond Law of Thermodynamics: disorder is more likely than orderentropy: disorder in the universeThe 2nd Law of Thermodynamics states that entropy is always increasing.89Laws of ThermodynamicsFree energy: the energy available to do work-denoted by the symbol G (Gibb’s free energy)enthalpy: energy contained in a molecule’s chemical bondsfree energy = enthalpy – (entropy x temp.)G = H - TS10Laws of ThermodynamicsChemical reactions can create changes in free energy:DG = DH - T DSWhen products contain more free energy than reactants – DG is positive.When reactants contain more free energy than products – DG is negative.11Laws of ThermodynamicsChemical reactions can be described by the transfer of energy that occurs:endergonic reaction: a reaction requiring an input of energy - DG is positiveexergonic reaction: a reaction that releases free energy - DG is negative1213Laws of ThermodynamicsMost reactions require some energy to get started.activation energy: extra energy needed to get a reaction started -destabilizes existing chemical bonds -required even for exergonic reactionscatalysts: substances that lower the activation energy of a reaction1415Energy Currency of CellsATP = adenosine triphosphate-the energy “currency” of cellsATP structure:-ribose, a 5-carbon sugar-adenine-three phosphates1617Energy Currency of CellsATP stores energy in the bonds between phosphates.Phosphates are highly negative, therefore: -the phosphates repel each other -much energy is required to keep the phosphates bound to each other -much energy is released when the bond between two phosphates is broken18Energy Currency of CellsWhen the bond between phosphates is broken:ATP ADP + Pi energy is releasedADP = adenosine diphosphatePi = inorganic phosphateThis reaction is reversible.1920Energy Currency of CellsThe energy released when ATP is broken down to ADP can be used to fuel endergonic reactions.The energy released from an exergonic reaction can be used to fuel the production of ATP from ADP + Pi.21EnzymesEnzymes: molecules that catalyze reactions in living cells-most are proteins-lower the activation energy required for a reaction-are not changed or consumed by the reaction22EnzymesEnzymes interact with substrates.substrate: molecule that will undergo a reactionactive site: region of the enzyme that binds to the substrateBinding of an enzyme to a substrate causes the enzyme to change shape, producing a better induced fit between the molecules.232425EnzymesMultienzyme complexes offer certain advantages:1. The product of one reaction can be directly delivered to the next enzyme.2. The possibility of unwanted side reactions is eliminated.3. All of the reactions can be controlled as a unit.26EnzymesNot all enzymes are proteins.Certain reactions involving RNA molecules are catalyzed by the RNA itself.ribozymes: RNA with enzymatic abilitiesFor example, the ribosome is a ribozyme.27EnzymesEnzyme function is affected by its environment.Factors that can change an enzyme’s 3-dimensional shape can change its function. -for example, pH, temperature, regulatory molecules28EnzymesTemperature -enzyme activity may be increased with increasing temp, up to the temp optimum-temperatures too far above the temp optimum can denature the enzyme, destroying its functionpH – most enzymes prefer pH values from 6 to 8.2930EnzymesInhibitors are molecules that bind to an enzyme to decrease enzyme activity.-competitive inhibitors compete with the substrate for binding to the same active site-noncompetitive inhibitors bind to sites other than the enzyme’s active site31EnzymesAllosteric enzymes exist in either an active or inactive state.-possess an allosteric site where molecules other than the substrate bind-allosteric inhibitors bind to the allosteric site to inactivate the enzymeallosteric activators bind to the allosteric site to activate the enzyme3233MetabolismMetabolism: all chemical reactions occurring in an organismAnabolism: chemical reactions that expend energy to make new chemical bondsCatabolism: chemical reactions that harvest energy when bonds are broken34MetabolismSome enzymes require additional molecules for proper enzymatic activity.These molecules could be:-cofactors: usually metal ions, found in the active site participating in catalysis-coenzymes: nonprotein organic molecules, often used as an electron donor or acceptor in a redox reaction35MetabolismBiochemical pathways are a series of reactions in which the product of one reaction becomes the substrate for the next reaction.Biochemical pathways are often regulated by feedback inhibition in which the end product of the pathway is an allosteric inhibitor of an earlier enzyme in the pathway.3637