2 There are 2 types of chemical reactions a) exothermic (exergonic):the amount of energy released is greater than the activation energyEnergy released
3 b) endothermic (endergonic): the amount of energy released is less than the activation energyEnergy must be supplied
4 Biological catalysts Proteins Specific Enzymes! A substance that speeds up a chemical reaction without being used up in the reaction
5 Enzymes ... are catalystsEvery reaction involves breaking bonds, that requires energy. The rate of a particular reaction depends on the activation energy necessary to initiate it.Catalysts reduce the activation of energy increasing reaction rates.
6 Enzymes ... are specific LOCK AND KEY MODEL chemist Emil Fischer. Proposed the lock and key model.KEY (substrate) has a specific shape (arrangement of functional groups and other atoms) that allows it and no other key to fit into the LOCK (the enzyme).
7 The substrate and enzyme complement each other Therefore, they can fit together, like a lock and key.Different molecules do not complement the enzyme's active site.
8 Enzymes ... are specific INDUCED FIT MODEL Daniel E. Koshland Jr. modified the lock-and-key modelHe proposed that binding of the substrate to the enzyme alters the configuration of both, providing a better fit.
9 Before binding, the substrate and enzyme do not exactly fit each other Binding of the substrate to the enzyme changes the configuration of both so that they fit together.Different molecules cannot induce a fit with the enzyme
11 Enzymes ... are affected by CONCENTRATIONIncrease substrate or enzyme concentration…Molecules more likely to collide…More reactions…Rates of reaction increases…Up to a point where the rxn reaches a maximum – saturation point.
12 Enzymes ... are affected by TEMPERATUREIncreasing temperature –Increases molecular movement …more likely for enzyme and substrate molecules to meet…Increases reaction rate.Low temp: H-bonds and interactions that give the enzyme its shape aren’t flexible enough to permit the induced fit for optimum reaction ratesHigh temp: H-bonds and interactions are too weak to maintain enzymes shape due to increased movement of atoms making up the enzyme
14 Enzymes ... are affected by pHEnzymes function at an optimum pHChanging pH results in a change of balance of the hydrogen ion concentration and therefore the balance between positively and negatively charged amino acids making up the enzymeChanges in the charges of the aa’s results in a change in the shape of the enzymeDifferent enzymes have different optimal pH’s
16 Enzymes ... can be denatured Denaturation = a structural change in a protein that results in a loss (usually permanent) of its biological properties.When exposed to high temperature or extremes of pH
17 InhibitionEnzyme activity can be inhibited which slows the rate of reactionCompetitive inhibitionNoncompetitive inhibitionExamples of inhibitors….Aspirin, Ibuprofin, DDT, Sarin nerve gas, PenicillinProtease inhibitors as a possible cure for AIDS
18 Competitive Inhibition Inhibiting molecule is structurally similar to the substrateIt binds to the active site preventing the substrate from bindingEnzyme inhibition
19 PenicillinThis antibiotic binds to active site of glycoprotein peptidase, an enzyme that forms the peptide bonds in peptidoglycan, a component of the bacterial cell wall (so is a competitive inhibitor.)With a weaker cell wall, bacteria are more susceptible to rupture by osmotic lysis and so fail to survivePenicillin GPenicillin V
20 Noncompetitive Inhibition Allosteric Inhibition –Inhibitor molecule binds to enzyme (not the active site)Causes a conformational change to active siteResulting decrease in activityRegulates metabolic pathways thru end product inhibition
21 Sarin Nerve GasInhibits the enzyme acetyl-cholinesterase, an enzyme in the body that plays a critical role in maintaining nerve function and control. When the enzyme is inhibited, a build-up of acetylcholine occurs at the nerve endings, causing symptoms that include blurred vision, profuse sweating and loss of motor function control. Paralysis many times follows.
22 Type of reaction catalyzed Classification of EnzymesEnzyme GroupType of reaction catalyzedExamplesOxidoreductasesTransfer of O & H atoms between substances, ie. all oxidation-reduction reactionsDehydrogenasesOxidasesTransferasesTransfer of a chemical group from 1 substance to anotherTransaminasesPhophorylasesHydrolasesHydrolysis reactionsPeptidasesLipasesPhosphatasesLyasesAddition or removal of a chemical group other than by hydrolysisDecarboxylasesIsomerasesThe rearrangement of grops within a moleculeMutasesLigasesFormation of bonds between 2 molecules using energy derived from the breakdown of ATPSynthestases
23 Naming of EnzymesStart with the name of the substrate upon which the enzyme acts, ie. succinateAdd the name of the type of the reaction which it catalyzes, ie. dehydrogenationConvert the end of the last word to an –ase suffix, ie. dehydrogenaseThus: succinic dehydrogenase