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UD BISC 207 - Chapter 6: Energy, Enzymes, & Metabolism

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Chapter 6: Energy, Enzymes, & MetabolismI. Metabolism - Sum of all chemical reactions in a cell/organismA. Organisms need a source of energy & a source of carbon: Fig. 6.1II. Energy - A system’s capacity to do workA. Can be converted between forms (ex. potentialkinetic)1. When energy changes forms, it’s conserved but less is available for work because of loss to entropy (i.e. heat, usually)B. Molecules contain potential energy1. Electrons farther from the nucleus have more potential energy2. Ex. ATP contains potential energy because of clustering of 3 negative O- chargesIII. Chemical Reactions – processes in which molecules are transformedA. Reactions have direction & rate1. Energy & concentration of reactants drive direction & rateB. H/G/T/S 1. H = G + TSa. H = enthalpy = total energyb. G = free energy (FE) = usable energy for workc. T = Temperatured. S = entropy or unusable energy2. G = H – TS3. ∆G = ∆H – T∆SC. Exergonic vs. Endergonic Reactions1. ∆G = ∆H – T∆S2. ∆G < 0: exergonic reaction (spontaneous, free energy released)a. Spontaneous – reaction that occur without an input of free energyi. May occur very slowly at a given temperatureii. Reaction rate (kinetics) is in depended of reaction spontaneity b. ATP Hydrolysis (ATP  ADP + P) is exergonici. ∆G = -7kcal/mol3. ∆G > 0: endergonic reaction, NOT spontaneous, requires input of free energy4. Cells couple exergonic & endergonic reactions to “push” the endergonic reaction forward a. Energy from the exergonic reaction is used to drive the endergonic oneD. Catabolism/Anabolism 1. Catabolic reactions/pathways: break down molecules & store energy in molecules (ex. ATP synthesis)2. Anabolic reactions: use energy to build moleculesIV. Enzymes A. Usually proteinsB. Big (compared to reactant molecules)C. Catalyze reactionsD. Specific to substratesE. Energy diagram: Reaction process vs. Free energy1. Transition state: highest energy state (peak)F. How enzymes decrease activation energy1. Reactants change shape when they bind with enzyme, which strains bond energya. Easier to remove molecules needed for reaction (ex. ATP  ADP + P)2. Reactants are close togethera. Some enzymes bind to both reactants needed for a reaction, increasing the likelihood that the reactants will contact each otherV. Metabolic Pathway – a coordinated series of chemical reactionsA. Each step is typically catalyzed by a single

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