Chapter8.pdf BIOLOGY 108 - 0001
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This 3 page Class Notes was uploaded by Koral Shah on Sunday September 20, 2015. The Class Notes belongs to BIOLOGY 108 - 0001 at University of Missouri - Kansas City taught by Marilyn Yoder in Fall 2015. Since its upload, it has received 40 views. For similar materials see General Biology I in Biology at University of Missouri - Kansas City.
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Date Created: 09/20/15
Chapter 8 An Introduction to Metabolism 81 Metabolism39s Transformation of Matter and Energy Metabolism all of an organism39s chemical reactions manages the material and energy resources of a cell Metabolic Pathway the path a molecule takes from beginning to after several reactions caused by enzymes Catabolic Pathways release energy by breaking down molecules ex cellular respiration Anabolic Pathways consume energy to build molecules ex synthesis of a protein from amino acids First Law of Thermodynamics the energy of the universe is constant it can be transferred but not created or destroyed Conservation of Energy Entropy a measure of disorder or randomness Second Law of Thermodynamics every energy transfer increases the entropy of the universe Spontaneous Process does not require any input of energy ex an old car rusting For a process to occur spontaneously it must increase the entropy of the universe Universe quotthe systemquot plus quotthe surroundingsquot 82 FreeEnergy Change Free Energy the portion of a system39s energy that can perform work when temperature and pressure are uniform throughout the system AGm AHm TASK Change in Free Energy Change In Total Energy Temperature X Change in Entropy Negative change in G spontaneous reaction Every spontaneous process decreases system39s free energy end product is more stable AG G nal Ginitial Free Energy Instability Example a glucose molecule is less stable more likely to break down than the simple molecules into which it can be split Equilibrium Maximum Stability As a reaction proceeds towards equilibrium free energy decreases A process is spontaneous and can do work only when it is moving towards equilibrium not at equilibrium Exergonic Reaction net release of free energy AG is negative moves towards equilibrium Note breaking of bonds doesn39t release energy it is the potential energy of creating new bonds Endergonic Reaction absorbs free energy from surroundings not spontaneous Metabolism never reaches equilibrium defining feature of life Constant ow of materials in and out of cells 83 Powers of ATP Cellular Work Chemical Work pushing of endergonic reactions that would not occur spontaneously ex synthesis of polymers from monomers Transport Work pumping of substances across membranes against direction of spontaneous movement Mechanical Work movement of chromosomes during cellular reproduction Energy Coupling use of an exergonic process to drive an endergonic one ATP contains sugar ribose nitrogenous base adenine and chain of 3 phosphate groups acts as immediate source of energy powering cellular work one nucleoside triphosphate used to make RNA bonds between phosphate groups can be broken by hydrolysis Phosphorylated Intermediate the hydrolysis of ATP usually results in the transfer of a phosphate group from ATP to this intermediate happens through coupling of exer and endogonic reactions ATP can be regenerated by adding phosphate to ADP MM e L 4 ATP 7 273 Endergonic Exergonic Energy from Energy for Cellular Respiration Cellular Work ADP i i Heat ltATP Cycle endergonic Catabolic exergonic pathways are used to power this endergonic reaction 84 Enzyme Catalysts Enzyme macromolecule usually protein that acts as a catalyst to speed up a reaction Activation Energy energy required to contort a reactant molecule so the bonds can break and the reaction can occur Transition State when reactants have absorbed enough energy for bonds to break and are unstable Energy Barrier reactants must get to that activation energy in order to react creating a barrierenter Enzyme Catalysts Enzymes can lower the Activation Energy required Substrate reactant an enzyme acts on Enzyme Substrate Complex binding of enzyme and substrate analogy lock and key Active Site restricted region of enzyme that binds to substrate Induced Fitchange in shape of enzyme to make the active site fit snugly around substrate substrate is held by weak hydrogen and ionic bonds Ways Enzymes Can Lower Activation Energy 1 Active site provides template for substrates to come together in a way that allows the reaction to occur 2 Enzyme may stretch the substrate toward their transitionstate form 3 Active site provides a microenvironment more conductive to particular reaction 4 Direct participation of the active site in the chemical reaction Environment Effects on Enzymes Higher Temperature to a point Higher Enzymatic Activity Optimal pH 68 Cofactors nonprotein helpers for catalytic activity Coenzyme if the cofactor is an organic molecule ex nutritional vitamins Competitive Inhibitors reduce productivity of enzymes by blocking substrates from entering active sites NonCompetitive Inhibitors do not directly compete with the substrate bind to another part of the enzyme to impede reaction Enzyme Inhibition Examples poisons antibodies etc Selective Inhibition naturally present in cell to regulate enzyme activity 85 Enzyme Regulation Allosteric Regulation protein39s function at one site is affected by binding of a regulatory molecule to a separate site may result in inhibition or stimulation to enzyme activity Activator stabilizes shape that has functional active sites ex ATP Inhibitor stabilizes inactive form of enzyme ex ADP Cooperativity amplifies response of enzymes to substrates Feedback Inhibition metabolic pathway switched off by inhibitory binding of its end product to an enzyme that acts early in the pathway ex when ATP inhibits an enzyme in an ATP generating pathway due to overstock of ATP