ATP Immediate source of energy that drives cellular work Adenosine triphosphate Nucleotide with unstable phosphate bonds Phosphate bonds easily hydrolyzed.

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ATPImmediate source of energy that drives cellular workAdenosine triphosphateNucleotide with unstable phosphate bondsPhosphate bonds easily hydrolyzedNucleoside: adenine joined to ribose3 phosphates attached to riboseATPnucleosideHydrolysis of unstable bonds between phosphatesTerminal phosphate bonds unstableProducts of hydrolysis more stableExergonic (spontaneous)Produces ADP + PG = -7.3kcal/mole in labIn living cell 13kcal/molATP performs workrequires enzymesExergonic hydrolysis coupled with endergonic phosphorylationPhosphorylation transfer of P to another moleculeMolecule receiving P becomes more activePage 95Regeneration of ATPContinual rapid process 107 molecules used and made/sec/cellADP + P ATPRequires energy --- how much?EndergonicEnzymesBiological catalysts: Most are proteinsSome are ribozymes-RNASpeed up rxns by lowering energy barriersEven if a reaction is spontaneous, it may take a really long time to get enough energy to start. (example digestion)Enzymes LOWER the amount of energy, helping spontaneous reactions to occur faster.Free energy of activation EAactivation energy Energy required to start a reaction (heat)Needed to get molecules to their transition state, unstable condition to break bondsSpontaneous reactions can be slowHeat can catalyze reactions, but heat is not good for all parts of the cell/bodySO, we have enzymes to catalyze reactions(Exergonic, spontaneous reactions)Activation energy changeActivation energy:With and without enzymesExample of a spontaneous reactionUrea + H2O CO2 + NH3 (Ammonia) Bacteria in air breakdown ureaAt room temperature and pH 8Time required 3 million yearsWith enzyme urease 30 000 molecules/sReview of enzymesCompositionLower EADo not changeVery selectiveSpecificity of enzymesDetermined by protein conformationSpecific to a substrateSubstrate: Substance an enzyme acts onActive site restricted region of an enzyme which binds to substratePocket or grooveEnzyme, substrates, and active siteChanges shape in response to substrateInduced fit change in shape of active siteOccurs as enzyme joins to substrateSpecific to a substrateInduced fit animationSteps in Catalytic CycleFormation of enzyme-substrate complexInduced fit (like clasping handshake)Side chains of a few amino acids catalyze conversion of substrate to productProduct departsEnzyme emerges in its original formMechanisms that lowerEA (Activation energy)Hold two or more reactants in proper position to reactInduced fit may distort substrates bond Active site might provide a micro-environment for reactionSide chains may participate directly in the reactionRate of ReactionHigher the substrate concentration the faster the reactionUp to a limitEnzyme can become saturated with substrate moleculesIf saturated rate depends upon how fast the active sites can convert substratesIf saturated to speed up, add enzymeConditions that favor enzyme activityOptimal temperatureOptimal pHCofactorsSmall non-protein molecules May bind to active site and substrateInorganic (zinc, iron, copper)Organic (vitamins), called coenzymesEnzyme InhibitorsCompetitive inhibitorsResemble substrateCompete for active site and block active site from substrateIf reversible (weak bonds) overcome by increased concentration of substrateCO binds to hemoglobinSarin, a nerve gas (binds to an enzyme in the nervous system)Competitive inhibitorNoncompetitive inhibitorsBind to another part of enzymeCauses change in shapeSubstrate can not bind to active siteMetabolic poisonsDDT, many antibioticsSelective inhibition is necessary in cell to regulate metabolism Competitive or noncompetitive inhibitor?Metabolic control: Allosteric regulationAllosteric siteSpecific receptor site on some part of the enzyme Two receptor sites: active and allostericEnzymes with these have two or more polypeptide chainsEach chain has active siteAllosteric site where subunits joinAllosteric enzymes have 2 conformationsOne conformation is activeThe other is inactiveActivator binds to allosteric to stabilize active site conformationInhibitor (noncompetitive) binds to allosteric site to stabilize the inactive conformationCooperativitySubstrate binds to active site of one subunitInduces a conformational change in other subunitsStabilizes active site in subunitsMore substrate can bind to other active sitesEX: Hemoglobin (4 active sites)Feedback InhibitionRegulation of metabolic pathwayEnd product inhibits enzyme within the pathwayPrevents cell from wasting chemical resourcesFeedback InhibitionTrue or False. Enzymes change the direction of the reaction.Describe the relationship between activation energy and enzymes.Describe the relationship between active sites and substrates.What is the difference between competitive inhibitors and noncompetitive inhibitors?True or False. All protein enzymes work at the same optimal pH.If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur?A. additional product will formB. additional substrate will formC. the reaction will change from endergonic to exergonicD. Nothing, the reaction will stay at equilibriumDescribe what allosteric regulation is.Allosteric activation would stabilize the _____________ form of the enzyme. Which means?True or False.The types of inhibition with enzyme-catalyzed reactions always have negative impacts on the organism.


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