Biol 1411 1st Edition Lecture 11 Outline of Last Lecture I Energy Requirements of Cell II ATP III Enzymes Outline of Current Lecture I Enzymatic inhibition II Bioenergetics Current Lecture Inhibitors naturally occurring and man made molecule that bind to the enzyme and slow the reaction rates Competitive inhibitors compete with the natural substrate for binding site Noncompetitive inhibitors bind to the enzyme at a different site and alter active site often function as metabolic regulators Reversible inhibitor bonds non covalently to the enzyme Irreversible inhibitor covalently bond to enzyme permanently inactive Allosteric Regulation a type of noncompetitive regulation Some enzymes exists in more than one shape o Active form can bind substrate o Inactive form cannot bind substrate Most allosteric enzymes are proteins with quaternary structure o Catalytic subunit with active site o Regulatory subunits to which a small molecule can mind o Effectors can inhibit or activate an enzyme Allosteric enzymes are important in regulating metabolic pathways o Are very sensitive to small changes in concentration or noncompetitive inhibitors Metabolic pathway navigation o The first reaction is the commitment step other reactions then happen in sequence o When enough of the end product is present the whole pathway will be turned off These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Feedback inhibition the final product acts as a noncompetitive inhibitor of the first enzyme Physical environment can also affect enzyme activity o pH Every enzyme is most active at a particular pH pH influences the ionization of functional groups o Temperature Every enzyme has an optimal temperature At high temps non covalent bonds begin to break Enzyme can lose its tertiary structure and become denatured Bioenergetics Fuels carbon based molecules whose stored energy can be released for use Energy is released through oxidation reactions that breakdown the fuel molecules into simpler molecules such as CO2 Glucose most common fuel in organisms Metabolic pathways o Each reaction is catalyzed by a specific enzyme o Metabolic pathways are similar in all organisms o In eukaryotes metabolic pathways are compartmentalized in organelles o Each pathway is regulated by key enzymes usually by allosteric mechanisms 3 metabolic pathways are involved in harvesting energy of glucose o Glycolysis glucose is converted to pyruvate o Cellular respiration aerobic and converts pyruvates into water and CO2 leads to syntheses of much ATP o Fermentation anaerobic and converts pyruvates into lactic acid or ethanol CO2 produces a little ATP Glycolysis most ancient process Re dox Reactions o Reduction gain of electrons o Oxidation lose electrons o Hydrogen atoms can also be involved in redox reactions o Are always coupled Glucose is oxidized and oxygen becomes reduced All of the e in glucose are transferred to molecules of oxygen to form water Glucose oxidation occurs in a series of controlled steps Catalyzed by enzymes Coenzyme NAD is a key electron carrier in redox reactions o NAD oxidized receives e0 from glucose o NADH reduced carries e from glucose to other molecules in the mitochondria ultimately on to O2 5 energy producing processes 3 pathways o Cellular respiration Glycolysis Pyruvate oxidation Citric acid cycle Electron transport ATP synthesis CO2 and H2O o Fermentation Glycolysis Fermentation Lactate or alcohol Glycolysis o Inputs Glucose 2 NAD 2ADP 2Pi o Outputs 2 molecules of pyruvate 2 NADH 2ATP net o 10 enzyme catalyzed reactions 1 5 energy investment 6 10 energy payout
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