1 Chapter 20 Enzymes and Vitamins 20.1 Enzymes Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Enzymes are Biological Catalysts Enzymes are proteins that  Catalyze nearly all the chemical reactions taking place in the cells of the body.  Increase the rate of reaction by lowering the energy of activation. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

3 Names of Enzymes The name of an enzyme  Usually ends in ­ase.  Identifies the reacting substance. For example, sucrase catalyzes the reaction of sucrose.  Describes the function of the enzyme. For example, oxidases catalyze oxidation.  Can be a common name, particularly for the digestive enzymes, such as pepsin and trypsin.

4 Enzymes are classified by the reaction they catalyze. ClassType of Reactions Catalyzed OxidoreductasesOxidation–reduction TransferasesTransfer groups of atoms Hydrolases Hydrolysis LyasesAdd atoms/remove atoms to or from a double bond IsomerasesRearrange atoms LigasesUse ATP to combine small molecules Classification of Enzymes

5 Oxidoreductases and Transferases Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

6 Hydrolases and Lyases Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

7 Isomerases and Ligases Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

8 Match the type of reaction with an enzyme. 1) aminase2) dehydrogenase 3) isomerase4) synthetase A. Converts a cis-fatty acid to a trans-fatty acid. B. Removes 2 H atoms to form a double bond. C. Combines two molecules to make a new compound. D.Adds NH 3. Learning Check

9 Match the type of reaction with an enzyme. 1) aminase2) dehydrogenase 3) isomerase4) synthetase A. 3 Converts a cis-fatty acid to a trans-fatty acid. B. 2 Removes 2 H atoms to form a double bond. C. 4 Combines two molecules to make a new compound. D. 1 Adds NH 3. Solution

10 Chapter 20 Enzymes and Vitamins 20.2 Enzyme Action Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

11 Active Site The active site  Is a region within an enzyme that fits the shape of the reacting molecule called a substrate.  Contains amino acid R groups that bind the substrate.  Releases products when the reaction is complete.  Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

12 Enzyme Catalyzed Reaction In an enzyme-catalyzed reaction  A substrate attaches to the active site.  An enzyme-substrate (ES) complex forms.  Reaction occurs and products are released.  An enzyme is used over and over. E + S ES E + P Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

13 Enzymes may recognize and catalyze  A single substrate.  A group of similar substrates.  A particular type of bond. Enzyme Specificity Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings TABLE 20.2

14 Lock and Key Model In the lock-and-key model of enzyme action,  The active site has a rigid shape.  An enzyme only binds substrates that exactly fit the active site.  Only substrates with the matching shape can fit.  The substrate is the key that fits that lock. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

15 Induced-fit Model In the induced-fit model of enzyme action,  Enzyme structure is flexible, not rigid.  Enzyme and substrate adjust the shape of the active site to bind substrate.  The range of substrate specificity increases.  Shape changes improve catalysis during reaction. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

16 Enzyme Catalyzed Reaction  The proper fit of a substrate (S) in an active site forms an enzyme-substrate (ES) complex. E + S ES  Within the ES complex, the reaction occurs to convert substrate to product (P). ES E + P  The products, which are no longer attracted to the active site, are released.  Overall, substrate is converted to product. E + S ES E + P

17 Example of An Enzyme Catalyzed Reaction Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

18 Learning Check A. The active site is (1) the enzyme (2) a section of the enzyme (3) the substrate B. In the induced fit model, the shape of the enzyme when substrate binds (1) stays the same (2) adapts to the shape of the substrate

19 Solution A.The active site is (2) a section of the enzyme B. In the induced fit model, the shape of the enzyme when substrate binds (2) adapts to the shape of the substrate

20 Isoenzymes  Catalyze the same reaction in different tissues in the body.  Such as lactate dehydrogenase (LDH), which converts lactate to pyruvate, consists of five isoenzymes.  Can be used to identify the organ or tissue involved in damage or disease.  Such as LDH have one form more prevalent in heart muscle and another form in skeletal muscle and liver.

21 Isoenzymes

22 Diagnostic Enzymes Diagnostic enzymes  Determine the amount of damage in tissues.  That are elevated may indicate damage or disease in a particular organ. TABLE 20.4

23 Diagnostic Enzymes Levels of enzymes CK, LDH, and AST  Are elevated following a heart attack.  Are used to determine the severity of the attack. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

24 Chapter 20 Enzymes and Vitamins 20.3 Factors Affecting Enzyme Activity Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

25 Temperature and Enzyme Action Enzymes  Are most active at an optimum temperature (usually 37°C in humans).  Show little activity at low temperatures.  Lose activity at high temperatures as denaturation occurs. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

26 Enzymes  Are most active at optimum pH.  Contain R groups of amino acids with proper charges at optimum pH.  Lose activity in low or high pH as tertiary structure is disrupted. pH and Enzyme Action Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

27 Optimum pH Values Enzymes in  The body have an optimum pH of about 7.4.  Certain organs, enzymes operate at lower and higher optimum pH values. TABLE 20.5 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

28 Enzyme Concentration An increase in enzyme concentration  Increases the rate of reaction (at constant substrate concentration).  Binds more substrate with enzyme. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

29 Substrate Concentration An increase in substrate concentration  Increases the rate of reaction (at constant enzyme concentration).  Eventually saturates an enzyme with substrate to give maximum activity. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

30 Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction. 1) no change 2) increase 3) decrease A. Increasing the concentration of sucrose B. Changing the pH to 4 C. Running the reaction at 70°C Learning Check

31 Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction 1) no change 2) increase 3) decrease A. 2 Increasing the concentration of sucrase B. 3 Changing the pH to 4 C. 3 Running the reaction at 70°C Solution

32 Chapter 20 Enzymes and Vitamins 20.4 Enzyme Inhibition Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

33 Inhibitors  Are molecules that cause a loss of catalytic activity.  Prevent substrates from fitting into the active sites. E + SESE + P E + I EI no P Enzyme Inhibitors

34 Competitive Inhibitor A competitive inhibitor  Has a structure that is similar to that of the substrate.  Competes with the substrate for the active site.  Has its effect reversed by increasing substrate concentration. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

35 A noncompetitive inhibitor  Has a structure that is much different than the substrate.  Distorts the shape of the enzyme, which alters the shape of the active site.  Prevents the binding of the substrate.  Cannot have its effect reversed by adding more substrate. Noncompetitive Inhibitor

36 Malonate and Succinate Dehydrogenase Malonate  Is a competitive inhibitor of succinate dehydrogenase.  Has a structure that is similar to succinate.  Inhibition is reversed by adding succinate. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

37 Irreversible Inhibition In irreversible inhibition, a substance  Bonds with R groups at the active site.  Destroys enzyme activity. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings TABLE 20.6

38 Identify each description as an inhibitor that is: 1) Competitive 2) Noncompetitive A. Increasing substrate reverses inhibition. B. Binds to enzyme surface, but not to the active site. C. Structure is similar to substrate. D. Inhibition is not reversed by adding more substrate. Learning Check

39 Identify each description as an inhibitor that is: 1) Competitive 2) Noncompetitive A. 1 Increasing substrate reverses inhibition. B. 2 Binds to enzyme surface, but not to the active site. C. 1 Structure is similar to substrate. D. 2 Inhibition is not reversed by adding more substrate. Solution

40 Chapter 20 Enzymes and Vitamins 20.5 Control of Enzyme Activity Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

41 Zymogens Zymogens (proenzymes)  Are inactive forms of enzymes.  Are activated when one or more peptides are removed.  Such as proinsulin is converted to insulin by removing a small peptide chain. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

42 Digestive Enzymes Digestive enzymes are  Produced as zymogens in one organ and transported to another such as the pancreas when needed.  Activated by removing small peptide sections. TABLE 20.7 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

43 Digestive Enzymes Zymogen Active Enzyme (from pancreas) (in small intestine) enteropeptidase trypsinogen trypsin + peptide trypsin chymotrypsinogen chymotrypsin + 2 dipeptides trypsin procarboxypeptidase carboxypeptidase + peptide

44 Allosteric Enzymes An allosteric enzyme is  An enzyme in a reaction sequence that binds a regulator substance.  A positive regulator when it enhances the binding of substrate and accelerates the rate of reaction.  A negative regulator when it prevents the binding of the substrate to the active site and slows down the rate of reaction.

45 Feedback Control In feedback control  A product acts as a negative regulator.  An end product binds with the first enzyme (E 1 ) in a sequence when sufficient product is present. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

46 Learning Check Identify each statement as: zymogen (Z)allosteric enzyme (A) positive regulator (PR)feedback control (FC) 1. An enzyme in a pathway that controls the rate of the reaction. 2. Speeds up a reaction by combining with an enzyme in the pathway. 3. Removal of a peptide activates the enzyme. 4. Some product binds to the first enzyme to limit the synthesis of product.

47 Solution Identify each statement as: zymogen (Z)allosteric enzyme (A) positive regulator (PR)feedback control (FC) 1. A An enzyme in a pathway that controls the rate of the reaction. 2. PR Speeds up a reaction by combining with an enzyme in the pathway. 3. Z Removal of a peptide activates the enzyme. 4. FC Some product binds to the first enzyme to limit the synthesis of product.

48 Chapter 20 Enzymes and Vitamins 20.6 Enzyme Cofactors and Vitamins Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

49 Enzyme Cofactors  A simple enzyme is an active enzyme that consists only of protein.  Many enzymes are active only when they combine with cofactors such as metal ions or small molecules.  A coenzyme is a cofactor that is a small organic molecule such as a vitamin.

50 Enzyme Cofactors Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

51 Function of Coenzymes A coenzyme prepares the active site for catalytic activity. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

52 Metal Ions as Cofactors Many active enzymes require a metal ion. Zn 2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

53 Some Enzymes and Their Cofactors TABLE 20.8 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

54 Learning Check Identify each enzyme as 1) A simple enzyme 2) An enzyme that required a cofactor A. Requires Mg 2+ for hydrolysis of phosphate esters. B. Requires vitamin B 3 to transfer an acetyl group. C. Is active with four polypeptide subunits.

55 Solution Identify each enzyme as 1) A simple enzyme 2) An enzyme that required a cofactor A. 2 Requires Mg 2+ for hydrolysis of phosphate esters. B. 2 Requires vitamin B 3 to transfer an acetyl group. C. 1 Is active with four polypeptide subunits.

56 Water-Soluble Vitamins Water-soluble vitamins are  Soluble in aqueous solutions.  Cofactors for many enzymes.  Not stored in the body. TABLE 20.9 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

57 Fat-Soluble Vitamins Fat-soluble vitamins are  Vitamins A, D, E, and K.  Soluble in lipids, but not in aqueous solutions.  Important in vision, bone formation, antioxidants, and blood clotting.  Stored in the body. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

58 Learning Check Identify each compound as a water-soluble vitamin (W) fat-soluble vitamin(F) 1. Folic acid 2. Retinol (Vitamin A) 3. Vitamin C 4. Vitamin E 5. Niacin

59 Solution Identify each compound as a: water-soluble vitamin (W) fat-soluble vitamin(F) 1. W Folic acid 2. F Retinol (Vitamin A) 3. W Vitamin C 4. F Vitamin E 5. W Niacin

60 Thiamin (Vitamin B 1 ) Thiamin  Was the first B vitamin identified.  Is part of the coenzyme thiamin pyrophosphate (TPP).  Is used to decarboxylate  -keto carboxylic acids.  RDA is 2 mg; deficiencies include fatigue, poor appetite, weight loss, nerve degeneration, heart failure  Sources are liver, yeast, whole grains, cereals, and milk.

61 Riboflavin (Vitamin B 2 ) Riboflavin  Is found in the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN).  Is needed for good vision and healthy skin.  RDA is 1.7 mg, deficiencies include dermatitis, dry skin, tongue inflammation, cataracts  Sources are liver, chicken, eggs, green leafy vegetables, dairy foods, peanuts, and whole grains. ribitol flavin

62 Niacin (Vitamin B 3 ) Niacin  Is part of the coenzyme nicotinamide adenine dinucleotide (NAD + ) involved in oxidation-reduction reactions.  RDA is mg.  Deficiency can result in dermatitis, muscle fatigue, and loss of appetite.  Sources are brewer’s yeast, chicken, beef, fish, liver, brown rice, and whole grains.

63 Pantothenic Acid (Vitamin B 5 ) Pantothenic acid  Is part of coenzyme A needed for energy production as well as glucose and cholesterol synthesis.  RDA is 10 mg; deficiency can result in fatigue, retarded growth, cramps, and anemia.  Is found in salmon, meat, eggs, whole grains, and vegetables.

64 Pyridoxine (Vitamin B 6 ) Pyridoxine and pyridoxal are  Two forms of vitamin B 6, which are converted to the coenzyme pyridoxal phosphate (PLP).  PLP is required in the transamination of amino acids and decarboxylation of carboxylic acids.  RDA is 1 mg; deficiency may lead to dermatitis, fatigue, and anemia.  Sources are meat, liver, fish, nuts, whole grains, spinach.

65 Cobalamin (Vitamin B 12 ) Cobalamin  Consists of four pyrrole rings with a Co 2+.  Is a coenzyme for enzymes that transfer methyl groups and produce red blood cells.  RDA is3 μg; deficiencies are pernicious anemia, nerve damage, and malformed red blood cells.  Sources are liver, beef, kidney, chicken, fish, milk products.

66 Ascorbic Acid (Vitamin C) Vitamin C  Is required in collagen synthesis, healing of wounds.  RDA is 60 mg; deficiencies are scurvy, weakened connective tissue, slow- healing wounds, and anemia.  Sources include: blueberries, citrus fruits, tomatoes, peppers, broccoli, red and green vegetables. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

67 Folic Acid (Folate) Folic acid (folate)  Consists of pyrimidine, p-aminobenzoic acid, and glutamate.  Forms the coenzyme THF used in the transfer of methyl groups and the synthesis of nucleic acids.  RDA is 0.4 mg; deficiencies are abnormal red blood cells, anemia, and poor growth.  Sources are green leafy vegetables, beans, meat, seafood, yeast, asparagus, and whole grains enriched with folic acid.

68 Folic Acid (Folate) Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

69 Vitamin A  Is needed for retinol (vision); synthesis of RNA.  RDA is 3 mg; deficiencies include night blindness, immune system repression, and slowed growth.  Sources are meats and beta-carotenes in plants, yellow and green fruits and vegetables. retinol beta-carotene

70 Vitamin D Vitamin D (D 3 )  Is synthesized in skin exposed to sunlight.  Regulates the absorption of phosphorus and calcium during bone growth.  RDA is 10 μg; deficiencies are weakened bones.  Sources are sunlight, cod liver oil, eggs, and enriched milk.

71 Vitamin E  Is an antioxidant in cells.  May prevent the oxidation of unsaturated fatty acids.  Is found in whole grains, and vegetables.  RDA is 10 mg; deficiencies are hemolysis and anemia.  Sources are meats, whole grains, vegetables, and vegetable oils.

72 Vitamin K  Vitamin K 1 in plants has a saturated side chain.  Vitamin K 2 in animals has a long unsaturated side chain.  Vitamin K 2 is needed for the synthesis of zymogens for blood clotting.  RDA is 80 μg; deficiencies are prolonged bleeding time, and bruising.  Sources are liver, spinach, and cauliflower. 3 n Vitamin K 1 (phylloquinone)Vitamin K 2 (menaquinone)

73 Learning Check Identify the vitamin associated with each 1) Thiamin (B 1 )2) Vitamin A 3) Vitamin K4) Vitamin D 5) Ascorbic Acid A. Collagen formation B. Beriberi C. Absorption of phosphorus and calcium in bone D. Vision E. Blood clotting

74 Solution Identify the vitamin associated with each 1) Thiamin (B 1 )2) Vitamin A 3) Vitamin K4) Vitamin D 5) Ascorbic Acid A. 5 Collagen formation B. 1 Beriberi C. 4 Absorption of phosphorus and calcium in bone D. 2 Vision E. 3 Blood clotting