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L42-44 - Berg Tymoczko Stryer Biochemistry Sixth Edition...

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1 1 Biochemistry Sixth Edition Chapter 15: Metabolism: Basic Concepts and Design Berg • Tymoczko • Stryer 2 Chpt 15 Metabolism: Basic Concepts and Design Metabolism centers on the energy currency of ATP. Mg 2+ -ATP 3 Major issues in metabolism: 1.) How does a cell extract energy and reducing power from its environment? 2.) How does a cell synthesize the building blocks of its macromolecules and then the macromolecules themselves. •There are more than 1,000 different chemical reactions in E. coli . •Yet there is a coherent design containing many common motifs: ATP currency and repeated appearance of a limited number of activated intermediates.
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2 4 Living organisms require an input of free energy for three major purposes: 1. Performance of mechanical work in muscle contraction and cellular movements. (Chpt 34) 2. Active transport of molecules and ions. (Chpt 13) 3. Synthesis of macromolecules and other biomolecules from simple precursors. (Chpts 24-31) Where does this free energy come from? 1. Photosynthetic organisms, or phototrophs , use sunlight. 2. Animals ( chemotrophs ) obtain energy through oxidation of foodstuffs generated by phototrophs. = 5 Metabolism: A linked series of chemical reactions that begins with a particular molecule and converts it into some other molecule(s) in a defined pathway 6 Metabolic Pathways •These pathways are interdependent and communicate via allosteric enzymes.
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3 7 Two broad classes of metabolic pathways 1.) Catabolic reactions (catabolism) e.g. oxidation (breakdown) of hydrocarbon release heat transform fuels into useful cellular energy (usually make ATP ). ATP-ADP cycle (more later) 2.) Anabolic reactions (anabolism) e.g. reduction (synthesis) of glucose, fats, DNA require energy (usually hydrolyze, or break ATP ) generate complex structures from simple ones Some pathways can be anabolic or catabolic, depending on the energy conditions in the cell. These pathways are referred to as amphibolic . 8 Metabolic pathways must satisfy two criteria: 1.) The individual reactions must be specific.
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