1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 4 Enzymes and Energy

2. I.Enzymes as Catalysts

3. Introduction to Enzymes 1.A class of proteins (exception – ribozymes are made of RNA) that serve as biological catalysts that: a.Increase the rate of a reaction b.Are not changed by the reaction (so can be used again) c.Do not change the nature of the reaction--the reaction could have occurred without the enzyme, just much slower d.Lowers the activation energy of the reaction

4. Activation Energy a.The energy required for the reactants to engage in a reaction b.Most molecules lack the activation energy for a reaction. 1)Adding heat increases the likelihood of a reaction occurring. This increases the rate of reactions. 2)Heat has some negative effects on cells. Catalysts help the reaction occur at lower temperatures.

5. Catalyzed vs. Noncatalyzed Reactions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Reactants Energy of reactants Activation energy Energy Number of reactant molecules Activation energy Energy released by reaction Products Noncatalyzed reaction Energy Number of reactant molecules Catalyzed reaction Products Energy released by reaction Activation energy Activation energy is lowered Energy of reactants Reactants

6. Mechanisms of Enzyme Activity 1.The function of an enzyme is dictated by its structure. 2.Each enzyme has a characteristic 3D shape or conformation, with pockets that serve as active sites in the enzyme. 3.The reactants are called substrates, and they fit into the active site like a key to a lock; called the lock-and-key model 4.Sometimes the initial fit is not exact but will change as the substrate moves into the active site; called the induced-fit model

7. Mechanisms of Enzyme Activity 5.When a substrate binds to the active site of an enzyme, it forms temporary bonds, weakening the original bonds of the substrate and allowing them to break easily. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A+B (Reactants) C+D (Products) Enzyme Substrate A Active sites Substrate B (a) Enzyme and substrates(b) Enzyme-substrate complex(c) Reaction products and enzyme (unchanged) Product D Enzyme Product C

8. Mechanisms of Enzyme Activity 6.New bonds are formed between substrates as they are brought close together by the enzyme. a.Bonding of enzyme to substrates forms a temporary enzyme-substrate complex. b.This breaks to yield the products of the reaction. c.The amount of enzyme in a sample of fluid can be measured based on the rate of product synthesis.

9. Naming Enzymes 1.The first enzymes discovered were given arbitrary names. An international committee later decided to end all enzymes with the suffix –ase. 2.They also decided to make the first part of the name apply to the function of the enzyme. a.Phosphatases remove phosphate groups. b.Synthetases and synthases catalyze dehydration synthesis. c.Hydrolases – promote hydrolysis d.Dehydrogenases – remove hydrogen atoms e.Kinases – add phosphate groups f.Isomerases – rearrange the atoms

10. Isoenzymes a.Because names are given to enzymes based on function, an enzyme that does the same job in two different organs has the same name. b.However, the molecules may be slightly different (in areas outside the active site) and are called isoenzymes; useful for detecting and diagnosing certain diseases c.Example: Creatinine phosphokinase (CK) exists in three forms – MM (in skeletal muscle), BB (in brain), and MB (in cardiac muscle)

11. Diagnostic Value of Measuring Enzymes in Blood

12. II.Control of Enzyme Activity

13. Enzyme Activity 1.Measured by the rate at which substrate is converted to product 2.Influenced by: a.Temperature b.pH c.Concentration of cofactors and coenzymes d.Concentration of enzyme and substrate e.Possible stimulatory or inhibitory effects of products on enzyme function

14. Effects of Temperature 1.An increase in temperature will increase the rate of reactions until the temperature reaches a few degrees above body temperature. 2.At this point, the enzyme is denatured. 10 Temperature (°C) 1003730 20 Enzyme activity 40

15. Effects of pH 1.Enzymes exhibit peak activity within a narrow pH range called the pH optimum. 2.pH changes will result in enzyme conformational changes 3.Optimum pH reflects the pH of the fluid the enzyme is found in a.Stomach vs. saliva vs. small intestine

16. Effects of location on optimum pH TrypsinSalivary amylase Pepsin 2 pH 64 Enzyme activity 810 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17. Coenzymes 1.Most enzymes need additional small molecules to aid in a reaction. 2.Coenzymes are organic molecules derived from water-soluble vitamins. 3.They transport hydrogen atoms and other small molecules between enzymes.

18. Cofactors 1.Cofactors help form the active site through a conformational change of the enzyme or help in enzyme-substrate binding. 2.Cofactors are metal ions such as, Ca 2+, Mg 2+, Mn 2+, Cu 2+, Zn 2+

19. Cofactors Substrates (a) Cofactor Enzyme (b) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20. Enzyme Activation 1.Enzymes, particularly of the digestive system, are often produced in inactive forms called a zymogens, which are activated after they are secreted into their target areas  Example: pepsinogen  pepsin 2.Activation requires phosphorylation (adding a phosphate) or dephosphorylation (taking away a phosphate). 3.Enzyme inhibition can be controlled through turnover, by which enzymes are degraded within lysosomes.

21. Substrate Concentrations 1.As the substrate concentration increases, so will the rate of the reaction until the enzyme becomes saturated 2.Saturated means that every enzyme in the solution is being used. 3.Adding more substrate will not increase the rate of the reaction

22. Substrate Concentrations Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Saturation Maximum rate Substrate concentration Reaction rate

23. Reversible Reactions 1.Sometimes a single enzyme can drive a reaction in two directions, depending on the concentration of substrate/product. 2.When one side gets higher, the other reaction reverses. 3.This is called the law of mass action. 4.Example: the enzyme carbonic anhydrase H 2 O + CO 2 ↔ H 2 CO 3

24. Metabolic Pathways 1.Most reactions are linked together in a chain (or web) called a metabolic pathway. 2.These begin with an initial substrate and end with a final product, with many enzymatic steps along the way. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initial substrate AF Final product Intermediates Enz 1 B Enz 2 Enz 3 Enz 4 Enz 5 DEC

25. Branched Metabolic Pathways a.Few metabolic pathways are linear. b.Most include branches where several products can be produced. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initial substrate A Enz 1 Intermediates Enz 2 B Enz 3' Enz 3 Enz 4' E' Enz 5' Enz 4 Enz 5 Final products F' F D' D C E

26. End Product Inhibition a.Branch points are often inhibited by a form of negative feedback in which one of the final products inhibits the branch point enzyme. b.In the process called allosteric inhibition, the product binds to the enzyme at a location away from the active site and changes the 3D conformation of the enzyme. c.Keeps the final product from accumulating

27. End Product Inhibition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Enz 1 A Enz 2 B – Enz 3 ' Inhibition if this final product accumulates. This pathway becomes favored FED Enz 3 D' Enz 4' Enz 5' 2 1 3 Enz 4 Enz 5 F'E' C

28. Inborn Errors of Metabolism a.Occur when there is a mutation in a single gene that codes for an enzyme in a metabolic pathway b.Products to be formed after this enzyme in the chain are not formed. c.Diseases occur due to loss of end product or accumulation of intermediary products (those before the bad enzyme) or alternative products in a branch.

29. Inborn Errors of Metabolism Enz 1 Enz 2 Abnormal gene makes defective enzyme (Enz 3 ). Enz 3' Production of these molecules increases and may cause disease. This pathway cannot be followed. Lack of “F” may cause disease. C BA 1 2 3 Enz 4' Enz 5' FED Enz 4 Enz 5 Enz 3 D'F'E' Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30. Examples of Diseases Caused by Inborn Errors of Metabolism

31. III.Bioenergetics

32. Laws of Thermodynamics  Bioenergetics - the flow of energy in living systems  First Law of Thermodynamics: Energy can not be destroyed or created, only transformed. a.The transformation is not 100%

33. First Law of Thermodynamics Conversion of light energy into glucose by plants Free energy C 6 H 12 O 6 (glucose) + 6 O 2 6 CO 2 + 6 H 2 O Energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34. Law of Thermodynamics  Second Law of Thermodynamics – energy is lost with each transformation as heat, so the available free energy (energy available to do work) decreases. 1)Entropy = degree of disorganization 2)Entropy increases at each step of energy transformation.  This law relates to endergonic and exergonic reactions.

35. Endergonic and Exergonic Reactions  Endergonic reactions a.Chemical reactions that require an input of energy. b.Products contain more free energy than the reactants. c.Occur in reactions where the reactants are at a greater state of entropy and the products are at a lesser state of entropy d.Example - plants need the energy from light to turn carbon dioxide and water into glucose.

36. Endergonic and Exergonic Reactions  Exergonic reactions a.Chemical reactions that produce energy. b.Products will have less free energy than the reactants. c.Example - breaking glucose down into carbon dioxide and water produces energy. d.Energy is used to make ATP for use in other endergonic reactions in the body.

37. Energy Obtained from Glucose Energy Total energy released 6 CO 2 + 6 H 2 O Combustion C 6 H 12 O 6 + 6 O 2 Free energy Cellular oxidation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

38. Calories a.The amount of energy in a molecule can be measured in calories. b.One calorie = amount of heat required to raise the temperature of 1 cubic centimeter of water 1 degree Celsius. c.Calories in food are actually reported in kilocalories (1,000 calories), but the term Calorie with a capital C is used

39. Coupled Reactions 1.Energy from the environment (food) is broken down in exergonic reactions to drive the endergonic reactions in our bodies. 2.Energy must be stored in a usable form, ATP a.The production of ATP is actually an endergonic reaction that is coupled to an exergonic reaction to drive it. b.The ATP molecule stores energy in its bonds to be used elsewhere. c.ATP is called the universal energy carrier.

40. Coupled Reactions How coupled reactions work. Products Reactants Endergonic reactionsExergonic reactions Reactants Products Free energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

41. Coupled Reactions Formation of ATP C C C N N N HH H + H O –O–O O P O OP O OP O Adenosine diphosphate (ADP) Inorganic phosphate (P i ) Adenosine triphosphate (ATP) NH 2 CH N HC OH CH 2 –O–O –O–O –O–O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

42. ATP as the Universal Energy Carrier Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP producedATP used for cell work ATP ADP + P i ATP Food ADP + P i ATP ADP + P i ATP CO 2 + H 2 O ATP

43. Coupled Reactions: Oxidation-Reduction 1.Reduction: when an atom or molecule gains electrons (is reduced) a.It is reduced in charge (electrons are negative). 2.Oxidation: when an atom or molecule loses electrons (is oxidized) a.Oxygen may not be involved 3.These reactions are always coupled. For one molecule to lose an electron, it has to give it to another molecule. a.Reducing agent: electron donor b.Oxidizing agent: electron receiver

44. Oxidation – Reduction 4.Many molecules can be both oxidizers and reducers in a chain reaction where electrons are passed along. 5.Oxygen is a great electron acceptor, which is why the process is called oxidation. Oxygen is not the only oxidizer, however. 6.Usually, free electrons are not passed along, but hydrogen atoms carrying the electrons are. a.A molecule that loses hydrogen is oxidized. b.A molecule that gains hydrogen is reduced.

45. Hydrogen carrier molecules a.NAD = nicotinamide adenine dinucleotide; comes from the vitamin niacin (B 3 ) b.FAD = flavin adenine dinucleotide; comes from the vitamin riboflavin (B 2 ) c.NAD and FAD are coenzymes that play an important role in hydrogen transfer. d.Each FAD can accept 2 electrons and bind to 2 protons, thus reduced FAD = FADH 2. e.Each NAD can accept 2 electrons and bind to 1 proton, thus reduced NAD = NADH + H +.

46. C O N + N NH 2 H H. + H H+H+ + 2 Oxidation and Reduction of NAD and FAD Two electrons added Reduced state FADH 2 (Rest of the molecule) FAD Oxidized state (b) Reaction site Reaction site (a) Reduced state NADH Oxidized state NAD + Reaction site Rest of the molecule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

47. Action of NAD Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. X Y X–H 2 NAD NAD is oxidizing agent (it becomes reduced) NADH is reducing agent (it becomes oxidized) Y–H 2 NAD NADH + H +