Metabolism: TCA Cycle and respiration

10/1/2012 Metabolism Is the Sum of All Chemical Reactions in the Cell • Series of related reactions form metabolic pathways • Some pathways are primarily energy-producing – this is catabolism • Some pathways are primarily using energy to build complex structures – this is anabolism or biosynthesis 10/1/2012 Review of Organic Chemistry • Most reactions in biochemistry are thermal heterolytic processes • Nucleophiles react with electrophiles • Heterolytic bond breakage often gives rise to transferable groups, such as protons • Oxidation of reduced fuels often occurs via transfer of electrons and protons to a dedicated redox cofactors Chemical Reactivity Most reactions fall within few categories: • Oxidations-reductions (e- transfers) • Group transfers (H+, CH3+, PO32-) • Cleavage and formation of C–C bonds • Cleavage and formation of polar bonds • Nucleophilic substitution mechanism • Addition–elimination mechanism • Hydrolysis and condensation reactions • Internal rearrangements • Eliminations (without cleavage) Group Transfer Reactions • Proton transfer, very common • Methyl transfer, various biosyntheses • Acyl transfer, biosynthesis of fatty acids • Glycosyl transfer, attachment of sugars • Phosphoryl transfer, to activate metabolites, also important in signal transduction 10/1/2012 10/1/2012 10/1/2012 10/1/2012 10/1/2012 10/1/2012 10/1/2012 10/1/2012 10 10/1/2012 Summary In this chapter, we learned that: • Citric acid cycle is an important catabolic process: it makes GTP, and reduced cofactors that could yield ATP • Citric acid cycle plays important anabolic roles in the cell • A large multi-subunit enzyme, pyruvate dehydrogenase complex, converts pyruvate into acetyl-CoA • Several cofactors are involved in reactions that harness the energy from pyruvate • The rules of organic chemistry help to rationalize reactions in the citric acid cycle 11 ... CH3+, PO32-) • Cleavage and formation of C–C bonds • Cleavage and formation of polar bonds • Nucleophilic substitution mechanism • Addition–elimination mechanism • Hydrolysis and condensation reactions... chapter, we learned that: • Citric acid cycle is an important catabolic process: it makes GTP, and reduced cofactors that could yield ATP • Citric acid cycle plays important anabolic roles in... transferable groups, such as protons • Oxidation of reduced fuels often occurs via transfer of electrons and protons to a dedicated redox cofactors Chemical Reactivity Most reactions fall within few categories: