2Questions to answer! Lesson Objectives What are enzymes? State the definition of enzymes.How do enzymes work?Explain the mode of action of enzymes in terms of active site, enzyme-substrate complex, lowering of activation energy, and enzyme specificity.Describe the characteristics of enzymes.3. What affects enzyme activity?Investigate and explain the effects of temperature, pH, on the rate of enzyme-catalyzed reactions.Where are enzymes used?State 1 enzyme-catalyzed process.Classify enzymes.
3What are enzymes?Definition of EnzymesWhat are catalysts? How do they work?Recall: What are proteins??Enzymes are biological catalysts, commonly made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction.Properties of enzymes
4condensation reaction What are enzymes?Recall: ProteinsBasic unit of proteins:How amino acids are linked up:Link between amino acids:Long chains of basic units:Polypeptides are folded and its 3D shape is held together by .Weak bonds can be broken by heat and chemicals. The protein is said to be .A denatured protein loses its .amino acidscondensation reactionpeptide bondpolypeptideweak bondsdenaturedfunctionSource: edu/deps/pstc/backup/heme.gif
5Enzymes are Biological Catalysts How do enzymes work?Enzymes are Biological CatalystsA catalyst is a substance which can alter or speed up a chemical reaction.Catalysts are not chemically-changed at the end of the reaction.
6Enzymes are Biological Catalysts How do enzymes work?Enzymes are Biological CatalystsEg: Decomposition of Hydrogen Peroxide…2H2O2 → 2H2O + O2This reaction can be sped up by a catalyst,manganese (IV) oxide.Videos:Dilute H2O2: H2O2 decompositionFresh H2O2: Last High School Chemistry ClassSource:com/prodimg/73864/200.jpg
7Enzymes are Biological Catalysts How do enzymes work?Enzymes are Biological CatalystsEg: Decomposition of Hydrogen Peroxide…2H2O2 → 2H2O + O2This reaction can be sped up by a catalyst,manganese (IV) oxide.2H2O H2O + O2 + HeatThe same amount of manganese (IV) oxide remains after the reaction. It is not changed during the reaction.Inorganic CatalystMnO2 (catalyst)
8Enzymes are Biological Catalysts How do enzymes work?Enzymes are Biological CatalystsThe enzyme CATALASE can speed up hydrogen peroxide decomposition.Enzymes are BIOLOGICAL CATALYSTS.Video: Nosebleed Chemistry2H2O H2O + O2 + HeatBiological Catalyst(Organic)Note: Catalase is also found in potatoes!Catalase (enzyme)How do enzymes work?
9How do enzymes work?Activation EnergyThe energy needed to start a chemical reaction is called activation energy.Once the reaction has received enough energy, the rest of the reaction occurs spontaneously.
10How do enzymes work?Activation EnergyEnzymes lower the activation energy required to start a chemical reaction.ReactantsProductsEnzymes do not change the energy level of reactants and products.Enzymes only lower the ‘height’ of the ‘activation energy hill.’
11Lock and Key Hypothesis How do enzymes work?Lock and Key HypothesisThe substances on which enzymes act are called substrates.Enzymes bind to substrates by the lock and key hypothesis.ABenzyme molecule is free to take part in another reactiona new substance (product) AB leaves the active sitesactive sitesABenzyme molecule (the ‘lock’)substrate molecules (A and B) can fit into the active sitesenzyme-substrate complex
12Lock and Key Hypothesis How do enzymes work?Lock and Key HypothesisEnzyme reaction depends on the presence of active sites.Active sites have a specific 3D shape.Specific substrate molecules fit into the active site like a lock and key.Substrate binds to the enzyme, forming an enzyme substrate complex.Reactions take place at the active sites to convert substrate molecule(s) into product molecule(s).Product molecule(s) separate, leaving the enzyme molecule unchanged and free to combine again with more substrate molecules.
13Lock and key hypothesis How do enzymes work?Induced Fit ModelCurrent hypothesis for enzyme actionWhen a substrate molecule fits into an enzyme molecule, the enzyme molecule alters its shape slightly so that it fits more tightly around the substrate molecule.This makes the chemical reaction easier.Lock and key hypothesisInduced Fit ModelSource:
14Enzyme Characteristics How do enzymes work?Enzyme CharacteristicsEnzymes are required in minute amountsEnzymes are very efficient molecules.They remain unchanged at the end of the reaction, and thus can be reused over and over again.A of enzyme can catalyze a of chemical reactions.small amountlarge amount
15Enzyme Characteristics How do enzymes work?Enzyme CharacteristicsEnzyme SpecificityEnzyme action is highly specific: each chemical reaction is catalyzed by a unique enzyme.The enzyme’s specificity is due to its 3-dimensional surface configuration.The shape of the substrate must be complementary to the shape of the enzyme’s active site.The shape of an enzyme can be affected by high temperature and acids and alkalis.
16Enzyme Characteristics How do enzymes work?Enzyme CharacteristicsEnzymes catalyze reversible reactionsSome reactions in living cells are reversible. They can proceed in the forward or backward direction.Some enzymes catalyze both forward and backward reactions until an equilibrium is reached. This occurs when the amount of reactants equals the amount of products formed.
17Enzyme Characteristics How do enzymes work?Enzyme CharacteristicsSome enzymes require coenzymesSome enzymes require a coenzyme (another compound) to be bound to them before they can catalyze reactions.Coenzymes are non-protein organic compounds.Eg. of coenzymes: Vitamin B complex
18What affects enzyme activity? 4 FactorsEnzymes are affected by the following:TemperaturepHEnzyme concentrationSubstrate concentration
19What affects enzyme activity? TemperatureEnzymes have an optimum temperature.This is the temperature at which the enzyme catalyzes the largest number of reactions per second.The optimum temperature of enzymes varies in different organisms, and is often but not always close to the temperature at which the enzyme usually functions.Some enzymes may have very high or very low optimum temperatures.
20What affects enzyme activity? TemperatureThe optimum temperature is reached. Enzyme is most active.3Rate of reaction(enzyme activity)Beyond the optimum temperature, enzyme activity decreases.4As the temperature rises, enzyme activity increases as indicated by the increase in the rate of reaction it catalyses. Usually the enzyme is twice as active for every 10°C rise in temperature until the optimum temperature is reached.2At point D, the enzyme has lost its ability to catalyse the reaction.5An enzyme is less active at very low temperatures.1K (optimum temperature)DTemperature
21What affects enzyme activity? TemperatureAs temperature rises…Particles of matter are in constant random motion.In the reaction, the enzyme and substrate molecules move and collide with one another at random.Raising the temperature increases the kinetic energy of the molecules.The substrate and enzyme molecules collide with each other more often, increasing the chance of substrates fitting into active sites.The rate of formation of enzyme-substrate complex increases, increasing the rate of formation of products.
22What affects enzyme activity? TemperatureAs temperature rises…Enzyme activity increases as the temperature increases up to the optimum temperature.At high temperatures, enzyme activity decreases.Enzymes are made of , and its 3D shape are held together by .At high temperatures, the vibrations of the atoms in the enzyme vibrate so violently that they break the weak bonds in the enzyme.The enzyme loses its shape and becomes denatured.The higher the temperature, the faster the rate of denaturation.proteinsweak bonds
23What affects enzyme activity? pHEnzymes are affected by the acidity or alkalinity of the solutions they are in.Acid or alkali can interact with the enzyme molecule, causing the protein to change its shape.Extreme changes in pH of the solutions denature the enzymes.Enzymes also have an optimum pH – the pH at which the enzyme can best function in.
26Enzyme & Substrate Concentration What affects enzyme activity?Enzyme & Substrate ConcentrationIn a solution of fixed enzyme concentration, as substrate concentration increases, the rate of reaction increases to a maximum.Beyond the maximum point, increasing the substrate concentration will not increase the rate of reaction.This is because at any point of time, all the enzyme molecules are in use. The enzyme molecules are saturated.The enzyme concentration becomes the limiting factor.The reaction rate will increase if the enzyme concentration is increased.
27Digestion Some food molecules are large and insoluble in water. Where are enzymes used?DigestionSome food molecules are large and insoluble in water.These food molecules cannot through the cell surface membrane.Some examples of large food molecules are , and .The large molecules must first be converted into simpler smaller substances which are soluble in water and diffusible.This is known as digestion, and is achieved by digestive enzymes.diffuseproteinsstarchfats
28CONDENSATION REACTION Where are enzymes used?DigestionEnzymes are involved in two types of reactions in the body:Synthesis of complex substances from simpler onesBreak down of complex substances to simpler onesCONDENSATION REACTIONHYDROLYTIC REACTIONSExamples of hydrolysis in the body:Large molecules of food are converted to smaller molecules by digestive enzymes.In cell respiration, glucose is broken down to carbon dioxide and water and release energy.Hydrogen peroxide can be produced in chemical reactions in cells. It is toxic to tissues. Cells produce enzyme catalase which catalyses the breakdown of hydrogen peroxide.Examples of condensation reactions in the body:Forming from glucoseForming proteins fromstarchamino acidsEnzymes catalyze practically ALL the chemical reactions that occur in an organism!
29Classification of Enzymes Where are enzymes used?Classification of EnzymesEnzymes are classified according to the chemical reactions they catalyze.Enzymes that catalyze hydrolytic reactions are known as hydrolases.Oxidation-reduction enzymes are involved in breaking down glucose during respiration.Enzymes were previously named by the persons who discovered them.Nowadays, enzymes are named according to a scientific system.
30Classification of Enzymes Where are enzymes used?Classification of EnzymesType of hydrolaseExample(s)Carbohydrases digest carbohydratesSalivary amylase (in the mouth) and pancreatic amylase. Both digest starch.Cellulases digest cellulose. It is produced by some bacteria. It is not found in mammals.Proteasesdigest proteinsPepsin in the stomachLipasesdigest lipids (fats)Lipase in pancreatic juice
31Where are enzymes used?Industrial UsesEnzymes are used in industry as they can bring about chemical changes at low temperature.Chemical reactions at low temperatures are easier to control and cheaper to run.Enzymes can be extracted from living cells and used in their pure form.
32Where are enzymes used?Industrial UsesMicroorganisms producing useful enzymes can be used in industry to make cheese, yoghurt and beer.Catalase can be added to latex containing hydrogen peroxide to produce oxygen to form foam rubber.Enzyme specificity makes them ideal for use in analysing chemicals.Enzymes can be used to detect glucose in urine.This can help to detect diabetes.Source: Kits&Equipment/SpecialLabFieldEquipt/G10_36.htmSource: images/large/011/11187.jpg
34Enzymes Definition of enzymes Pure Biology Chapter 5Definition of enzymesEnzymes are biological catalysts, commonly made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction.Enzymeshave specificareFunctionsProteinsasRemain chemically unchanged at the end of the reactionBiological catalystsareformspeed upEnzyme-substratecomplexRate ofreactionaffected byInactivatedDenaturedEnzymeconcentrationSubstrateconcentrationpHTemperaturewith the help ofbyat lowat highby loweringareofat extremeCoenzymesLock-and-keyhypothesisInduced-fitmodelActivationenergyChemical reactionsinvolveIntracellularenzymesExtracellularenzymesfound inDigestivesystemexamplesis theSpecific bindingof enzymeLipasesProteasesCarbohydrasestodigestdigestdigestSubstrateLipidsProteinsCarbohydratesto formto formto formto formSpecificproduct(s)Fatty acids and glycerolAmino acidsSimple sugars
35Remain chemically unchanged at the end of the reaction Pure Biology Chapter 5Definition of enzymesEnzymeshave specificareFunctionsasRemain chemically unchanged at the end of the reactionBiological catalystsareformspeed upEnzyme-substratecomplexRate ofreactionaffected byInactivatedDenaturedEnzymeconcentrationSubstrateconcentrationwith the help ofbyat lowat highby loweringareofat extreme changes ofCoenzymesInduced-fitmodelChemical reactionsinvolveIntracellularenzymesExtracellularenzymesfound inexamplesis theSpecific bindingof enzymeLipasestodigestdigestdigestSubstrateProteinsCarbohydratesto formto formto formto formSpecificproduct(s)Simple sugars