3 Define the following terms: Anabolic reactions:Catabolic reactions:Metabolism:Catalyst:Metabolic pathway:Specificity:Substrate:Product:Reactions that build up moleculesReactions that break down moleculesCombination of anabolic and catabolic reactionsA substance that speeds up reactions without changing the produced substancesSequence of enzyme controlled reactionsOnly able to catalyse specific reactionsThe molecule(s) the enzyme works onMolecule(s) produced by enzymes
4 Naming enzymes: Intracellular enzymes Extracellular enzymes Recommended namesSystematic nameClassification numberWork inside cells eg.DNA polymeraseSecreted by cells and work outside cells eg. pepsin, amylaseShort name, often ending in ‘ase’ eg. creatine kinaseDescribes the type of reaction being catalysed eg.ATP:creatine phosphotransferaseEg
5 Timeline of enzyme discovery 1835:Breakdown of starch to sugar by malt1877:Name enzyme coined to describe chemicals in yeast that ferment sugars1897:Eduard Buchner extracted enzyme from yeast and showed it could work outside cells1905:Otto Rohm exyracted pancreatic proteases to supply enzymes for tanning1926:James B Sumner produced first pure crystalline enzyme (urease)and showed enzymes were proteins:Protein nature of enzymes finally established when digestive enzymescrystallised by John H Northrop1946: Sumner finally awarded Nobel prize
6 Enzymes lower the activation energy of a reaction of uncatalysed reactionsInitial energy stateof substratesActivation energyof enzyme catalysedreactionEnergy levels of moleculesFinal energy state of productsProgress of reaction (time)
7 Enzymes lower activation energy by forming an enzyme/substrate complex Substrate + EnzymeEnzyme/substrate complexEnzyme/product complexProduct + Enzyme
8 In anabolic reactions enzymes bring the substrate molecules together. In catabolic reactions the enzyme active site affects the bonds in substrates so they are easier to break
9 Lock-and-key hypothesis assumes the active site of an enzyme is rigid in its shape How ever crystallographic studies indicate proteins are flexible.
10 The Induced-fit hypothesis suggests the active site is flexible and only assumes its catalytic conformation after the substrate molecules bind to the site.When the product leaves the enzyme the active site reverts to its inactive state.
11 Enzymes are globular proteins Active site has a specific shape due to tertiary structure of protein.A change in shape of the protein affects shape of active site and the function of the enzyme.Click to link to jmol interactive representation courtesy of University of Arizona
12 Characteristics of enzymes Only change the rate of reaction. They do not change the equilibrium or end products.Specific to one particular reactionPresent in very small amounts due to high molecular activity: Turnover number = number of substrate molecules transformed per minute by one enzyme moleculeCatalase turnover number = 6 x106/min
13 How would you measure the effect of an enzyme? Compare uncatalysed rate with catalysed.Enzymes can increase rate by a factor of between 108 to 1026
14 Characteristics of enzymes Rate of enzyme action is dependent on number of substrate molecules presentVmax = maximum rate of reactionVmax approached as all active sites become filledRate of Reaction (M)Some active sites free at lower substrate concentrationsSubstrate concentration
15 Why do scientists measure the initial rate of reaction of enzyme-catalysed reactions? They measure rate at start of reaction before any factors, eg. substrate concentration, have had time to change.Rate of Reaction (M)Independent variable
16 Rate of enzyme –catalysed reactions are affected by temperature. Temperature coefficient Q10:rate of reaction at (x + 10) oCQ10 =rate of reaction at x oCQ10 for between oC is 2
17 Enzymes denature at 60oCOptimum temperatureEnzyme denaturing and losing catalytic abilitiesRate doubles every 10oCRate of reactionTemperatureSome thermophilic bacteria have enzymes with optimumtemperatures of 85oC
18 pH affects the formation of hydrogen bonds and sulphur bridges in proteins and so affects shape. trypsincholinesterasepepsinRate of Reaction (M)246810pH
19 Enzymes in medicineGlucose oxidase + peroxidase + blue dye on dipsticks to detect glucose in urine:Glucose oxidaseGlucoseHydrogen peroxideperoxidaseDye: Blue---Green---BrownDye changes according to amount of glucoseEnzyme-linked immunosorbent assays (ELISAs) detect antibodies to infections.
20 Now answer the exam questions The first question you will complete and then swap with your partner. You will then mark each others work using the provided mark-scheme. You must agree each others marking.The second question you will complete and mark your own and then I will mark it and see if I agree with your marking.The third question you will complete and I will mark it. You will then check my marking and we will agree a score.The total score for all three questions will be recorded.