7.014 Handout 2007 Lectures 1 & 2 The Biosphere and Carbon and Energy MetabolismThus all life is run on the free energy difference between O2 and organic carbon (glucose). The autotrophs synthesize glucose using solar or chemical energy, which is broken down through respiration (either their own or that of the organisms that eat them) to provide the energy necessary for "biological work". Redox reactions are central to all these energy transformations, and the resulting flows of electrons manifest themselves in the form of biogeochemical cycles. The activities of bacteria keep these cycles moving. For example, the chemosynthetic bacteria oxidize many essential elements in the process of getting the energy required to reduce CO2. Certain anaerobic bacteria, in turn, reduce these compounds in the process of anaerobic respiration, i.e., they use these compounds as an electron acceptor in the absence of oxygen. This keeps the element cycles flowing and keeps the system from "running down".7.014 Lecture Handout Carbon and Energy Metabolism 2HeterotrophsFermentationglucose2 pyruvatelactate orCO2 + ethanol2 ADP + 2 Pi2 ATP2 NAD+2 NADHRespirationglucosepyruvateKrebs'CycleCO2ATPNAD+NADHNADHNAD+NADHNAD+e-ABH+ gradient(Quantities of compounds omitted for simplicity.)ADP + PiATPTypeaerobicsulfate-reducingdenitrifyingAO2SO42-NO3-BH2OH2S or SNO , N2,N2O, NH3 ⇒⇒⇒7.014 Lecture Handout Carbon and Energy Metabolism 3Photosynthesis(common to all)ADP + PiATPNADP+NADPH(Quantities of compounds omitted for simplicity.)glucoseCO2"Dark Reactions"AutotrophsLIGHTDCNADP+NADPHe-H+ gradientADP + PiATPDO2S, SO42-CH2OH2STypeoxygenic (plant)anoxygenic⇒⇒ 7.014 Lecture Handout Carbon and Energy Metabolism 4Autotrophs, continued:"Dark Reactions"CO2glucose(Quantities of compounds omitted for simplicity.)NADPHNADP+ATPADP + Pi(common to all)⇒⇒⇒⇒⇒⇒DCe-H+ gradientADP + PiATPChemosynthesisEFe-CDNADP+NADPHTypesulfur-oxidizing nitrifyingCH2SH2SNH3,NO2-DS, SO42-S, SO42-NO3-EO2NO3-O2FH2ON2OH2O(releases energy)(requires energy)(requires energy) 7.014 Lecture Handout Carbon and Energy Metabolism
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