CHAPTER 6 Metabolism 6 1 Cells and Energy Flow Energy ability to do work or bring about change Food chemical energy composed of organic molecules converted to ki netic energy mechanical energy with walking Plants capture only a small portion of solar energy most dissipates to heat All captured solar energy eventually dissipates as heat energy flow not cycle Laws of Thermodynamics 1 Law of conservation of energy energy cannot be created or destroyed but can change form 2 Energy cannot change forms without a loss of usable energy every energy transformation makes the universe less organized and more disordered No process requiring a conversion of energy is 100 efficient Entropy relative amount of disorganization 6 2 Metabolic Reactions and Energy Transformations Metabolism sum of chemical reactions that occur in a cell A reaction will occur spontaneously if it increases the entropy of the universe or if the free energy content of the reactants is less than that of the products Free energy is the amount of energy available after a chemical reaction has occurred Exergonic reactions spontaneous release energy endergonic reac tions require energy input Exergonic reactions can be used to drive endergonic reactions coupled re actions Endergonic more popular in body protein synthesis nerve conduction and muscle contraction ATP breakdown can be coupled to endergonic reactions to minimize energy loss 39 of free energy of glucose is transformed to ATP the rest is lost by heat 6 3 Metabolic Pathways and Enzymes Ribozymes biological catalysists that are made of RNA instead of proteins A metabolic pathway is a series of linked reactions Molecules do not react with one another unless they are activated in some way Energy of activation energy that must be added to cause molecules to re act with one another Enzymes lower the amount of energy required for activation energy content remains the same Enzyme Substrate Enzyme substrate Complex Enzyme Product in duced fit model Trypsin digests protein by breaking peptide bonds Enzymes are usually named for their substrates and end in ase The presence of particular enzymes can determine the products and direction of metabolism Rate of a reaction is the amount of product per unit time dependent on amount of substrate Each enzyme has an optimal pH pepsin 2 Trypsin 8 Cofactors inorganic ions Zn Fe or nonprotein organic molecules coen zymes at active site Vitamins organic molecules required for synthesis of coenzymes Niacin deficiency pellagra skin disease Riboflavin deficiency cracks at the corners of mouth 6 4 Organelles and Energy Flow In photosynthesis water has been oxidized and carbon dioxide has been re duced NADP In cellular respiration glucose has been oxidized and oxygen has been re duced NAD Electron transport chain ETC pass e between characters to release en ergy for ATP production An ATP synthase complex is a carrier protein for enzymes allows H through Chemiosmosis the production of ATP due to a hydrogen ion gradient across a membrane