Enzymes

1. Enzymes

2. Lesson 1

3. The Need for Speed • In order to survive, organisms need to carry out essential processes like respiration and photosynthesis • Under laboratory conditions, these reactions would take too long to occur and life would not be possible at all • Furthermore, some of these reactions would require conditions that cannot be achieved in the cell eg. High pressure, high temperature • To speed up these processes in the cell and to make them occur more easily, catalysts are needed • (See W_out_Enzm)

4. Catalysts Alter speedof chemical reactions Remain chemicallyunchanged at the end of the reaction Remove the need forextreme conditionse.g. high temperature or pressure

5. KClO4 KCl + 2O2 (g) KClO4 (s) KClO4 (l) KCl + 2O2 (g) KClO4 (l) The Decomposition of KClO4 (p. 72) High temperature (without catalyst) Lowrate of reaction Low temperature (without catalyst) Onlychange of physical stateobserved! Low temperature (with catalyst) Highrate of reaction Same mass of catalystretrieved at the end of the reaction  No chemical change in catalyst

6. Catalysts Alter speedof chemical reactions Remain chemicallyunchanged at the end of the reaction Remove the need forextreme conditionse.g. high temperature or pressure

7. Enzymes Biologicalcatalystsmade up ofprotein Sensitive tohigh temperaturesandextreme changes in pH Alter rate of reaction Remain chemically unchanged Such conditions break bondswithinthe protein molecules Proteins change inshape(denaturation) Remove the need for extreme conditionse.g. high temperature or pressure Change in shape causes decrease in/loss ofenzyme activity

8. Structure-function relationship Breakage of weak bonds Enzyme changes its shape Decrease in/loss of enzyme activity

9. Activation Energy, Ea (p. 73) • all reactions involve converting the reactant/s into the product/s:Reactant/s Product/s • In enzyme reactions, the reactant/s are calledsubstrates: Substrate/s Product/s • Before any reaction can occur, the reactants must obtain a certain amount of energy called theactivation energy • Once the activation energy is reached, thereaction can proceed, forming the products from the substrates • If the activation energy is never reached, the reactants willremain as reactants

10. Activation Energy, Ea - Activation energy is thus the energy needed to start a chemical reaction

11. Energy profile diagram (uncatalyzed) [p. 73] Ea = 100 – 50 = 50 kJ/mol 100 kJ/mol Activation energy, Ea Rxts 50 kJ/mol Pdts 20 kJ/mol 10s 1s 5s

12. When Ea is not reached… (See EA)

13. How enzymes work [p. 73] • for most reactions in the cell, the activation energy can only be attained without enzymes by havinghigh temperatures or pressures this isnot possible for living cells • Enzymes make these reactions possible bylowering the activation energyof the reactions: • (i) Reactant molecules need less energy to undergo a reaction • Reactions can occur at body temperatureandwithout any need for high pressure (ii) Easier forindividual moleculestoundergo a reaction • Rate of reaction isincreased Note:Rate of reactionrefers to thenumberof product molecules producedper unit time(pdt molecules/s)

14. How enzymes work - By lowering the activation energy, enzymes allow reactions to occur more quickly and easily

15. Lowering of activation energy (Ea Eacat) p. 73, Fig. 5.2

16. Uses of enzymes - enzymes are used for a wide range ofmetabolic reactions - Generally, metabolic reactions are of two types: a)Catabolic reactions (breaking down) e.g. breakdown of starch to maltose and proteins to amino acids b)Anabolic reactions (building up) e.g. formation of starch from glucose and fats from fatty acids and glycerol Metabolism Catabolism Anabolism

17. Catabolic reactions • involve thebreakdownofcomplex substancesintosimpler substances • May be carried out for nutrition, respiration, excretion and other essential processes - Breakdown of complex substancesmay be necessary fortransport of nutrients and wastesthroughout the body  e.g. digestion of food, aerobic respiration  See p. 74-75 (See Amylase)

18. Catabolic reactions

19. Anabolic reactions - involve thebuilding upofcomplex substancesfromsimpler substances - May be carried out for growth, development, storage of food and other essential processes  e.g. formation of fats from fatty acids and glycerol, formation of proteins from amino acids  See p. 75 (See Anabolic_rxn)

20. Anabolic reactions

21. A Double-edged Sword - because of thehighefficiency of enzymes, there is sometimes a need tocontrol their activity  For example,digestive enzymesmustonly be produced when they are neededor theywill attack cellular structurese.g. stomach wall  enzyme activity may also be controlled by producing the enzyme in aninactive formandactivating it only when the enzyme activity is required e.g. prorennin, trypsinogen Control of production Regulating enzyme action Production in an inactive form

22. Industrial applications of enzymes • Enzymes are used to produce a wide variety of products like beer, wine, bread and cheese. • They are also used in laundry detergents. • Enzymes are used in industry for the following reasons: a) Allow production at low temperatures and pressures b) High rate of production c) Specificity of action (e.g. ClinistixTM test strip)

23. Enzyme Nomenclature and Classification - when enzymes were first discovered, they were named by the people who discovered them usuallyno relationbetween theenzyme name, what it doesandwhat its substrate is  The name of the enzymecatalasedoes not hint that itworks on hydrogen peroxide, or that its function is tobreak down hydrogen peroxideto giveoxygenandwater(p. 75) - this method of naming enzymes led to muchconfusionand wasnot systematic a scientific system for naming enzymes was required

24. Enzyme Nomenclature and Classification - To make the process of naming enzymessystematic, enzymes were namedaccording to certain rulesandclassified according to the chemical reactions they catalyze - The rules in question are: 1) The name of thesubstratemust be reflected in thename of the enzyme 2) The name of the enzymemustend in‘-ase’ e.g. lipase, sucrase, maltase  Thus,glucose oxidasehasglucose as a substrateandfunctions to oxidize glucose  The‘-ase’ endingof the name reminds people that thesubstance is an enzyme(rather than a hormone, neurotransmitter or other type of biological molecule)

25. Enzyme Nomenclature and Classification - Enzymes can beclassifiedaccording to thechemical reactions they catalyze  e.g. there is a group of enzymes calledhydrolasesthat catalyze a type of reaction calledhydrolysis  in hydrolysis,wateris used tobreak down complex substances into simpler substances(catabolic reaction)  Hydrolasescan be further classified ascarbohydrases, proteasesandlipases, depending on whatthe substrate for the enzyme is  See p. 76 for details

26. Lesson 2

27. Speed upchemical reactions Affected bytemperature Characteristics of Enzymes Required in onlyminute amounts Affected bypH Reversibilityof reactions Specificin action May requirecofactors

28. Characteristics of Enzymes 1)Speed upchemical reactions - does this bylowering the activation energyneeded tostart the reaction 2) Requiredonly in minute amounts - because of thehigh efficiencyof enzymes, just asmall amount of enzymeis needed for avery large amount of substrate/s - Because enzymes arenot changed(used up) in their reactions, thesame enzyme moleculescan beused over and over again 3)Specificityof action - enzymes are highly specific in their action  Will usually catalyze onlyone type of reactionandact on one substrate/group of related substrates

29. Characteristics of Enzymes  e.g. amylases actonly on starchand not proteins or fats  Amylases areonly capable of catalyzing hydrolytic reactions and not other types of reactions like oxidation-reduction reactions - Thespecificityof enzymes means thateach type of reactionin the cell musthave a distinct enzyme/group of enzymes to catalyze it each enzyme isuniquein itsfunctionand thetype of substrate used - The specificity of enzymes can be traced to each enzyme’sdistinctive three-dimensional structureorsurface configuration - Thelock and key hypothesisexplains how theshape of an enzymeaffectsthe way it functions

30. Specificity of Enzymes Lock and key hypothesis Induced fit hypothesis

31. Lock and key hypothesis - according to thelock and key hypothesis, enzyme reaction depends on the presence ofactive sites - Active sites aredepressionsor‘pockets’on thesurfaceof an enzyme molecule into which thesubstrate molecules can fit(like a lock and key)  Enzyme is lock and substrate is key (See Enzm_SnF) (See Enzm_Concepts, II)

32. Lock and key hypothesis Steps in an enzyme-catalyzed reaction: 1) Substratebinds to the enzyme, forming anenzyme-substrate complex 2)Reactionstake place at theactive siteto convert thesubstrate molecules into product molecules 3)Product moleculesleave the active sitesto allownew substrate molecules to bind to the enzyme(Enzyme molecule remainsunchangedat the end of the process)

33. Lock and key hypothesis

34. Lock and key hypothesis Points to note: 1) Enzyme and substrate must becomplementary to each other(fit each other nicely) so that therequired reactions can take place at the active site 2)Only the substrate can fit into theactive site(not other enzymes or products) to give an enzyme-substrate complex

35. The Induced Fit model - the lock and key hypothesis makes the assumption thatenzymes arerigidmolecules that willonly interact with substrates that arecomplementary to them - Recent research suggests thatenzymes are moreflexiblethan previously thought - It is believed that theenzyme can actuallyalter its shapeslightlyin order tobind the substratemore tightly this tighter binding allows the chemical reaction to occureven more easily - Once the reaction has occurred and the products released from the enzyme, the enzyme regains itsoriginal shapeuntilanother substrate molecule binds to it (See Enzm_Concepts, III)

36. The Induced Fit model

37. The Induced Fit model Rigid Slightly flexible Not absolute Absolute Changes when the substrate is bound Remains the same throughout Returns to its original shape when the products are formed and released

38. Characteristics of Enzymes 4) Affected bytemperature -increasein temperatureincreasesenzyme activity, up to theoptimum temperature 5) Affected bypH -increasein pHincreasesenzyme activity, up to theoptimum pH

39. Characteristics of Enzymes A + B C + D 6)Reversibilityof reactions - some of the reactions catalyzed by enzymes arereversible  These reactions can go either waybut in most systems, adynamic equilibriumis reached  In such a situation, theratio of substrates to products becomes fixed  This ratio isrestoredevery time there is achangein either theconcentration of substratesor theconcentration of products - in living systems, the products may be quicklyremovedorused upsuch that the reactionkeeps being ‘pushed’ in one direction(substrate products OR pdts  substr)  reaction appears to be going inonly one direction

40. D D D C C C A A A A A B B B B B Reversibility of Reactions Assume rates of reaction are equal. Forward reaction A + B C + D Dynamic equilibrium is reached. Reverse reaction

41. D D D D C C C C A A A B B B Reversibility of Reactions Forward reaction A + B C + D Reverse reaction

42. Characteristics of Enzymes 7) May requirecofactorsto function e.g. Zn2+ in carbonic anhydrase - cofactors arenon-protein chemical compoundsthat arebound to an enzymeand arerequired for catalysis - May beinorganic(e.g. metal ions),organicorboth - Whenorganicandloosely bound to the enzyme,are calledcoenzymese.g. vitamin C

43. Speed upchemical reactions Affected bytemperature Characteristics of Enzymes Required in onlyminute amounts Affected bypH Reversibilityof reactions Specificin action May requirecofactors

44. Structure of Enzymes - Enzymes areproteins - Like all proteins, they are made up ofamino acidsstrung together bypeptide bonds all proteins are initially produced as astraight polypeptide chainby theribosome - After the chain is completed, it isfoldedto form acharacteristicthree-dimensional structure - It is thisstructurethat determines theenzymes’ abilityto catalyze reactions (formation of active site)

45. Folding Denaturation Structure of Enzymes - Tomaintainthe three-dimensional structure,weak hydrogen bondsare formedwithin the protein molecule - If thesehydrogen bonds are broken, the enzyme willlose its three-dimensional structureand with it, itsfunction (destruction of active site)

46. Enzyme activity vs Temperature - enzyme activityincreaseswithincreasingtemperature, up till the enzyme’soptimum temperature - At theoptimum temperature,enzyme activity is at itsmaximum - Beyondthe optimum temperature, enzyme activitydecreaseswithincreasingtemperature - At the denaturation temperature, the enzyme becomesdenaturedandloses its function(enzyme activity = 0) p. 80-81

47. Enzyme activity vs Temperature p. 80-81

48. Optimum Temperature - The optimum temperature of an enzyme varies in different organisms and has to be determined experimentally.  For most enzymes, optimum temperature is about 40 to 45 °C  The optimum temperature is often (but not always) close to that at which an enzyme functions

49. Enzyme activity vs Temperature(Before the optimum) - Before the optimum temperature is reached,increasingtemperatureincreasesenzyme activity 1) Astemperature increases, rate ofsuccessfulenzyme-substrate collisions increases  Successful collisions are those in which the substrate molecules manage to fit into the active sites with at least the activation energy 2) Hence, rate offormation of ES complexes increases 3) Hence, rate ofproduct formation / reaction increases

50. Enzyme activity vs Temperature(At the optimum) - At the optimum temperature, the rate ofsuccessful collisionsis at itsmaximum - Although theenergy of the enzyme moleculesis high, theinternal hydrogen bonds are still intactand interactionsbetween enzyme and substratearenot hindered Maximumrate ofproduct formation / reaction