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Lec 1 Metabolism main points.docx

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Biological Sciences
Course Code
Daman Bawa

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Metabolism - total network of chemical rxns carried out by a living cell used to acquire and use energy from the envt • Anabolic rxns - biomolecules synthesized form simpler components (biosynthesis) • Catabolic rxns - nutrients and cell constituents are broken down to salvage their components and/or to generate energy (degradation) • Metabolism is sum of these two rxns Bioenergetics - biochemical transformation of energy • Usually metabolism of ATP (NADH, NADPH) • Most important pathways r memb-associated electron transport in oxidative phosphorylation and photosynthesis WHAT IS INVOLVED IN THE STUDY OF METABOLISM? • Thermodynamics, free energy • Rxn kinetics, pathway flux (rate of flow), regulatory mechanisms • Enzymes • Biosynthesis and breakdown of organic compounds • Oxidation and reduction rxns • Electron Transport and photosynthesis Catabolism -> 3 stages 1. Large molecules in food are broken down into smaller units - digestion • Proteins -> aa's • Polysaccharides -> simple sugars • Fats -> glycerol and fatty acids • Absorbed by cells of the intestine and distributed throughout the body • No useful energy captured 1. Smaller mole's are degraded/modified further to a few simple units that play a key role in metabolism • Mostly the acetyl part of Acetyl CoA • Some energy ATP produced 1. Complete oxidation of fuel mole's, produce most of the energy • Common pathways (Citric acid cycle, oxidative phosphorylation) • Most of the ATP is synthesized via oxidative phosphorylation in mitochondria METABOLIC PATHWAYS - an interconnected series of rxns where the product of 1 rxn becomes the substrate for the next rxn • First committed step - every metabolic pathway has an irreversible rxn early in the pathway that locks the product in that particular pathway • Individual rxns must b specific (i.e. 1 product but could be multiple rxns?) • An entire series of rxns must be thermodynamically favorable • Pathways proceed in 1 direction (irreversible) -> anabolic & catabolic pathways differ 3 TYPES OF METABOLIC PATHWAYS 1. Linear -product of 1 rxn is the reactant in the next rxn e.g. glycolysis 1. Circular (catalytic) -series of rxns that regenerate the initial reactant e.g. citric acid cycle 1. Spiral -series of repeated rxns that break down or synthesize large molecules by removing / adding small units e.g. break down / synthesis of fatty acids (2 C at a time) WHY BOTHER WITH PATHWAYS? • Enzymes generally only catalyze 1 specific rxn • Allow for efficient managemt of energy • Molecules r synthesized or degraded by diff routes -allows metabolites to be shunted to / from other pathways -allows multiple control points -allows the coupling of energetically unfavourable rxns to favourable ones (take energy derived from 1 rxn to drive the next) Synthesis need to add a lot of energy -> too big energy barrier -develop in small increments METABOLIC RXNS ARE ENZYME-MEDIATED ROLE OF ENZYMES IN METABOLIC RXNS • Couple rxns (nrg yielding rxn to energy consuming rxn) • Stabilize transition states (↓energy) -stabilize high nrg transition states that would make a rxn unfavorable ENZYMES HAVE COMMON FEATURES • High substrate specificity • Active site -3-D cleft that binds substrate -small portion of total protein -multiple intermolecular sites of attraction w substrate -unique microenvironment • Conformational change on binding • Regulatory sites (specific inhibition) • Use of cofactors or co-enzymes ENZYMES AND RXN TYPES RECUR THROUGHOUT METABOLISM • Coupled rxns • Activated carriers •
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