General, Organic & Biological Chemistry, 5e (Timberlake) Chapter 20 Enzymes and Vitamins 20.1 Multiple-Choice Questions 1) Compared to an uncatalyzed reaction, an enzyme-catalyzed reaction A) uses less substrate B) produces different products C) occurs at a faster rate D) requires more energy E) requires a higher temperature Answer: C Objective: 20.1 Global Outcomes: GO2 2) Which of the following is NOT a step in the enzyme-catalyzed conversion of a substrate to product? A) The substrate binds to the enzyme away from the active site B) The substrate binds in the active site to form the E-S complex C) The enzyme assists in the conversion of the substrate to product D) The product is released from the active site E) A new substrate molecule binds to the enzyme for a new cycle Answer: A Objective: 20.1 Global Outcomes: GO2 3) The formation of an enzyme-substrate complex is the step in enzyme action A) first B) second C) third D) fourth E) last Answer: A Objective: 20.1 Global Outcomes: GO2 4) The active site of an enzyme A) is remote from the site of substrate attachment B) is converted to a product C) catalyzes the reaction D) increases the energy of reaction E) includes the entire enzyme Answer: C Objective: 20.1 Global Outcomes: GO2 Copyright © 2016 Pearson Education, Inc 5) The general function of an enzyme in the body is to A) catalyze chemical reactions B) maintain a neutral pH C) act as a reactant in carbohydrate storage D) maintain homeostasis E) eliminate waste products from the blood Answer: A Objective: 20.1 Global Outcomes: GO2 6) Most enzymes are A) fluid-mosaic proteins B) induced proteins C) substrate proteins D) fibrous proteins E) globular proteins Answer: E Objective: 20.1 Global Outcomes: GO2 7) In any reaction catalyzed by an enzyme, the reacting molecule is called the A) substrate B) cofactor C) coenzyme D) isozyme E) allostere Answer: A Objective: 20.1 Global Outcomes: GO2 8) When a substance bonds to an enzyme for reaction, its place of binding is the A) allosteric site B) primary pocket C) end pocket D) primary site E) active site Answer: E Objective: 20.1 Global Outcomes: GO2 9) Substances that react under the influence of an enzyme are usually held to the enzyme by A) peptide bonds B) side chains of amino acids in the enzyme protein C) ester bonds D) pH changes E) competitive inhibition Answer: B Objective: 20.1 Global Outcomes: GO2 10) Urease catalyzes only the hydrolysis of urea, and no other substrates This limited activity is called A) absolute specificity B) extreme specificity C) rigid specificity D) noncompetitive specificity Copyright © 2016 Pearson Education, Inc E) hyperspecificity Answer: A Objective: 20.1 Global Outcomes: GO2 11) The presence of enzymes to catalyze bioreactions in our bodies allows A) us to eat non-nutritious substances without consequence B) the activation energy of a reaction to be raised C) the rate of a desired chemical reaction to slow down D) bioreactions to occur under extreme conditions of temperature and pH E) bioreactions to take place under mild conditions Answer: E Objective: 20.1 Global Outcomes: GO2 12) Hexokinase catalyzes only the addition of phosphate to any hexose sugar This type of activity is called A) regional specificity B) collateral specificity C) group specificity D) noncompetitive specificity E) general specificity Answer: C Objective: 20.1 Global Outcomes: GO2 13) In the lock-and-key model of enzyme action, the enzyme active site is thought of as A) a rigid, nonflexible shape that fits the substrate exactly B) an area of the enzyme that can adjust to fit the substrate shape C) a key-like shape that fits into a pocket of the substrate surface D) a hydrophilic area on the enzyme surface E) a lock that bars a noncompetitive inhibitor from reacting Answer: A Objective: 20.1 Global Outcomes: GO2 Copyright © 2016 Pearson Education, Inc 14) In the induced-fit model of enzyme action, the enzyme active site A) stays the same shape during substrate binding B) adjusts shape to adapt to the shape of the substrate C) stays the same shape while causing a change in the shape of the substrate D) uses an inhibitor to adjust its shape for the substrate E) uses a cofactor to change the shape of a substrate Answer: B Objective: 20.1 Global Outcomes: GO2 15) The function of the enzyme-substrate complex is to provide an alternative reaction pathway that A) lowers the energy of the products B) lowers the energy of the substrate C) changes the concentration of the substrate D) decreases the activation energy for the reaction E) changes the possible product formed Answer: D Objective: 20.1 Global Outcomes: GO2 16) How many generalized steps are there in the reaction of an enzyme (E) with a substrate (S) to form and release the product (P)? A) one B) two C) three D) four E) five Answer: C Objective: 20.1 Global Outcomes: GO2 17) An increase in concentration of the enzyme LDH in the blood can be used to detect A) heart attack B) kidney damage C) anemia D) uremia E) bulimia Answer: A Objective: 20.2 Global Outcomes: GO7 Copyright © 2016 Pearson Education, Inc 18) Creatine kinase can be used in the diagnosis of A) hepatitis B) rickets C) heart attack D) prostatitis E) cancer Answer: C Objective: 20.2 Global Outcomes: GO7 19) To what main class of enzymes does the enzyme that catalyzes the conversion of lactose to galactose and glucose belong? A) oxidoreductase B) transferase C) hydrolase D) lyase E) isomerase Answer: C Objective: 20.2 Global Outcomes: GO2 20) To what main class of enzymes does the enzyme that catalyzes the following reaction belong? O OH | CH3 C COO → CH3 C HCOOA) oxidoreductase B) transferase C) hydrolase D) lyase E) isomerase Answer: A Objective: 20.2 Global Outcomes: GO2 21) To what main class of enzymes does the enzyme that catalyzes the following reaction belong? Ser - Ala → Ser + Ala A) oxidoreductase B) transferase C) hydrolase D) lyase E) isomerase Answer: C Objective: 20.2 Global Outcomes: GO2 22) The hydrolysis of ester bonds in triglycerides is catalyzed by a(n) A) lipase B) lyase C) isomerase D) hydrolase Copyright © 2016 Pearson Education, Inc E) oxidoreductase Answer: A Objective: 20.2 Global Outcomes: GO2 23) The optimum temperature for sucrase activity is 37 °C The hydrolysis of sucrose is slowest at which temperature in the choices below? A) °C B) 10 °C C) 20 °C D) 25 °C E) 45 °C Answer: A Objective: 20.3 Global Outcomes: GO2 24) "Physiological conditions" for reactions within the body are approximately A) pH and 37 °C B) pH and 37 °C C) pH and 37 °F D) pH and 273 °C E) pH and 273 K Answer: B Objective: 20.3 Global Outcomes: GO2 25) "Physiological pH", the pH for optimum activity for most enzymes, is a pH equal to A) 3.0 B) 5.4 C) 7.4 D) 8.6 E) 9.0 Answer: C Objective: 20.3 Global Outcomes: GO2 Copyright © 2016 Pearson Education, Inc 26) Most enzymes are deactivated permanently above a temperature of about A) 25 °C B) 37 °F C) 40 °C D) 45 °F E) 50 °C Answer: E Objective: 20.3 Global Outcomes: GO2 27) The surface of a freshly cut apple turns brown because of A) inhibition of the surface enzymes by nitrogen B) interaction of the surface enzymes with oxygen C) a change in pH at the surface D) an increase in substrate concentration at the cut surface E) the presence of vitamin C in the apple Answer: B Objective: 20.3 Global Outcomes: GO2 28) In an enzyme-substrate reaction, when excess substrate is present, increasing the concentration of the enzyme will A) increase the number of substrate molecules available B) inhibit the formation of products C) increase the decomposition rate of the enzyme-substrate complex D) decrease the turnover rate for the substrate E) increase the amount of reaction occurring Answer: E Objective: 20.3 Global Outcomes: GO2 29) Consider an enzymatic reaction in which the initial concentration of substrate is low If the amount of enzyme is held constant, but the amount of substrate is increased, the rate of an enzyme catalyzed reaction will A) increase in an exponential fashion B) decrease at first, then increase in a linear fashion C) increase at first in a linear fashion, then remain at a constant high rate D) stay the same E) be inhibited by the higher concentrations of substrate Answer: C Objective: 20.3 Global Outcomes: GO2 Copyright © 2016 Pearson Education, Inc 30) Urea is converted to ammonia and carbon dioxide by the action of urease What will be the effect on the rate if the temperature of the reaction is lowered from 37 °C (the optimum temperature) to 27 °C? O NH2 - C - NH2 + H2O 2NH3 + CO2 A) There will be no effect B) The rate will slow down C) The rate will double D) The rate will triple E) The rate will slow down, then speed up again Answer: B Objective: 20.3 Global Outcomes: GO2 31) Pepsinogen is an example of a(n) A) coenzyme B) cofactor C) isoenzyme D) allosteric enzyme E) zymogen Answer: E Objective: 20.4 Global Outcomes: GO2 32) When an end product from an enzyme-mediated sequence is also an inhibitor for an earlier step in the reaction sequence, the process is referred to as A) feedback control B) competitive inhibition C) irreversible inhibition D) negative catalysis E) concentration control Answer: A Objective: 20.4 Global Outcomes: GO2 33) Allosteric enzymes can control their output of product by A) binding the substrate at a site away from the active site B) binding an irreversible inhibitor at the active site C) binding a positive or negative regulator at a noncompetitive site D) changing the pH in the active site E) reversible inhibition using the product as the inhibitor Answer: C Objective: 20.4 Global Outcomes: GO2 Copyright © 2016 Pearson Education, Inc 34) A competitive inhibitor is one that A) binds to the enzyme at a site far from the active site B) binds to the active site in place of the substrate C) destroys the substrate D) binds to the allosteric site on an enzyme E) forms a complex with the substrate Answer: B Objective: 20.5 Global Outcomes: GO2 35) An irreversible inhibitor is one that A) forms hydrogen bonds with the substrate B) binds to the enzyme with hydrophobic interactions C) reacts covalently with the substrate D) binds covalently to the enzyme active site E) reacts covalently with a cofactor Answer: D Objective: 20.5 Global Outcomes: GO2 36) A noncompetitive inhibitor has a structure that A) does not resemble the substrate structure B) resembles the active site of the enzyme C) can bind to the active site of the enzyme D) does not interfere with the enzyme-substrate complex formation E) causes a change in the shape of the substrate Answer: A Objective: 20.5 Global Outcomes: GO2 37) Penicillin functions as an antibiotic by A) poisoning bacteria with toxins B) raising the temperature of a bacterium C) bonding to metal ions in bacterial electron transport systems D) inhibiting the enzymes for cell wall formation in bacteria E) acting as an acetylcholinesterase inhibitor Answer: D Objective: 20.5 Global Outcomes: GO2 Copyright © 2016 Pearson Education, Inc 38) A compound that binds to the surface of an enzyme, and changes its shape so that a substrate cannot enter the active site, is called a(n) A) irreversible inhibitor B) proenzyme C) cofactor D) noncompetitive inhibitor E) competitive inhibitor Answer: D Objective: 20.5 Global Outcomes: GO2 39) Some insecticides kill insects by inhibiting the enzyme A) alcohol dehydrogenase B) acetylcholinesterase C) creatine kinase D) lipase E) penicillinase Answer: B Objective: 20.5 Global Outcomes: GO2 40) Penicillin-resistant bacteria can survive treatment with penicillin because they produce the enzyme A) sucrase B) penicillin kinase C) penicillinase D) bacteriase E) phosphate lyase Answer: C Objective: 20.5 Global Outcomes: GO2 41) Which of the following is NOT true for a competitive inhibitor? A) It occupies the active site B) It cannot be converted to products C) It has a structure similar to the substrate D) Increasing the substrate concentration can reverse competitive inhibition E) It binds to the enzyme at a site remote from the active site Answer: E Objective: 20.5 Global Outcomes: GO2 10 Copyright © 2016 Pearson Education, Inc 42) A noncompetitive inhibitor A) binds at the active site of the enzyme B) alters the three-dimensional structure of the enzyme C) increases the rate of the enzyme-catalyzed reaction D) has a structure similar to the substrate E) has its effect reversed by adding more substrate Answer: B Objective: 20.5 Global Outcomes: GO2 43) Pepsinogen is an example of a(n) A) coenzyme B) cofactor C) isoenzyme D) allosteric enzyme E) zymogen Answer: E Objective: 20.6 Global Outcomes: GO2 44) When an end product from an enzyme-mediated sequence is also an inhibitor for an earlier step in the reaction sequence, the process is referred to as A) feedback control B) competitive inhibition C) irreversible inhibition D) negative catalysis E) concentration control Answer: A Objective: 20.6 Global Outcomes: GO2 45) Allosteric enzymes can control their output of product by A) binding the substrate at a site away from the active site B) binding an irreversible inhibitor at the active site C) binding a positive or negative regulator at a noncompetitive site D) changing the pH in the active site E) reversible inhibition using the product as the inhibitor Answer: C Objective: 20.6 Global Outcomes: GO2 11 Copyright © 2016 Pearson Education, Inc 46) The water-soluble B and C vitamins supply A) essential amino acids B) substrates necessary for most of the reactions in the body C) essential fatty acids D) coenzymes required by some enzymes E) competitive inhibitors needed to regulate enzyme activity Answer: D Objective: 20.6 Global Outcomes: GO7 47) Metal ions such as Zn2+ and Fe3+ are often needed by enzymes as A) isozymes B) allosteres C) inhibitors D) cofactors E) substrates Answer: D Objective: 20.6 Global Outcomes: GO2 48) When a cofactor is a small organic molecule, it is known as a(n) A) isoenzyme B) vitamin C) zymogen D) coenzyme E) regulator Answer: D Objective: 20.6 Global Outcomes: GO2 49) Iron(II) and iron(III) ions are used in the functioning of A) urease B) alcohol dehydrogenase C) creatine kinase D) the cytochrome oxidase system E) pepsin Answer: D Objective: 20.6 Global Outcomes: GO2 50) The B vitamins are examples of A) water-soluble vitamins B) essential amino acids C) essential minerals D) oil soluble vitamins E) vitamins that are stored in the liver Answer: A Objective: 20.6 Global Outcomes: GO2 51) Coenzymes such as water-soluble vitamins are needed in only small amounts because A) only small amounts of enzymes are present in each cell B) only small amounts of substrates are available at any one time C) they can be eliminated in the urine D) each vitamin molecule can be reused many times as a cofactor E) they can be stored in the liver for future use Answer: D 12 Copyright © 2016 Pearson Education, Inc Objective: 20.6 Global Outcomes: GO2 20.2 Bimodal Questions 1) A biological catalyst is called a(n) A) lipid B) enzyme C) cofactor D) coenzyme E) substrate Answer: B Objective: 20.1 Global Outcomes: GO2 2) The names of many enzymes can be recognized by the suffix A) -ate B) -ite C) -ose D) -ine E) -ase Answer: E Objective: 20.1 Global Outcomes: GO2 3) An enzyme that converts a cis double bond to a trans double bond is classified as a(n) A) oxidoreductase B) transferase C) hydrolase D) lyase E) isomerase Answer: E Objective: 20.2 Global Outcomes: GO2 13 Copyright © 2016 Pearson Education, Inc 4) The full name of the enzyme LDH is A) lactate dehydrogenase B) liver decompensation hexase C) lactate dehydrase D) liver dihydrogen kinase E) lipase dehydrogenase Answer: A Objective: 20.2 Global Outcomes: GO2 5) Enzymes that catalyze the same reactions but have slightly different structures are called A) coenzymes B) cofactors C) isoenzymes D) competitive E) noncompetitive Answer: C Objective: 20.2 Global Outcomes: GO2 6) An enzyme that removes H from a substrate is classified as a(n) A) oxidoreductase B) transferase C) hydrolase D) lyase E) isomerase Answer: A Objective: 20.2 Global Outcomes: GO2 7) The optimum pH for the activity of pepsin is about A) 2.0 B) 4.0 C) 6.5 D) 7.4 E) 7.6 Answer: A Objective: 20.3 Global Outcomes: GO2 8) The optimum pH for the activity of trypsin is about A) 2.0 B) 4.0 C) 6.5 D) 7.4 E) 8.0 Answer: E Objective: 20.4 Global Outcomes: GO2 9) Another name for a zymogen is a(n) A) cofactor B) coenzyme C) prosthetic group D) isozyme E) proenzyme 14 Copyright © 2016 Pearson Education, Inc Answer: E Objective: 20.5 Global Outcomes: GO2 10) One deficiency disease that can be traced to insufficient intake of vitamin D is A) scurvy B) rickets C) beriberi D) pellagra E) pernicious anemia Answer: B Objective: 20.6 Global Outcomes: GO2 11) A diet very low in vitamin C can lead over time to the condition A) rickets B) scurvy C) cancer D) carpal tunnel syndrome E) anorexia nervosa Answer: B Objective: 20.6 Global Outcomes: GO2 20.3 Short Answer Questions Indicate whether each of the following is fat soluble or water soluble 1) vitamin B6 Answer: water soluble Objective: 20.6 Global Outcomes: GO2 2) vitamin A Answer: fat soluble Objective: 20.6 Global Outcomes: GO2 3) pantothenic acid Answer: water soluble Objective: 20.6 Global Outcomes: GO2 4) ascorbic acid Answer: water soluble Objective: 20.6 Global Outcomes: GO2 5) vitamin E Answer: fat soluble Objective: 20.6 Global Outcomes: GO2 6) vitamin K Answer: fat soluble Objective: 20.6 Global Outcomes: GO2 15 Copyright © 2016 Pearson Education, Inc 7) niacin Answer: water soluble Objective: 20.6 Global Outcomes: GO2 8) folic acid Answer: water soluble Objective: 20.6 Global Outcomes: GO2 9) vitamin D Answer: fat soluble Objective: 20.6 Global Outcomes: GO2 10) riboflavin Answer: water soluble Objective: 20.6 Global Outcomes: GO2 20.4 True/False Questions 1) The active site is a large part of an enzyme Answer: FALSE Objective: 20.1 Global Outcomes: GO2 2) In the induced fit model of enzyme activity, both the enzyme and the substrate change shape Answer: TRUE Objective: 20.1 Global Outcomes: GO2 3) Alanine transaminase is an example of a transferase enzyme Answer: TRUE Objective: 20.2 Global Outcomes: GO2 4) Pyruvate carboxylase is an example of a ligase enzyme Answer: TRUE Objective: 20.2 Global Outcomes: GO2 5) Urease is an example of an oxidoreductase enzyme Answer: FALSE Objective: 20.2 Global Outcomes: GO2 6) The optimum pH of most cellular enzymes is about 7.4 Answer: TRUE Objective: 20.3 Global Outcomes: GO2 7) Phosphorylation is a common form of covalent modification Answer: TRUE Objective: 20.4 Global Outcomes: GO2 8) Insulin and digestive enzymes are produced as inactive forms called zymogens 16 Copyright © 2016 Pearson Education, Inc Answer: TRUE Objective: 20.5 Global Outcomes: GO2 9) Enzymes always require a cofactor Answer: FALSE Objective: 20.6 Global Outcomes: GO2 10) Enzyme cofactors are always metal ions, such as Zn 2+ and Fe3+ Answer: FALSE Objective: 20.6 Global Outcomes: GO2 11) Vitamins are often cofactors Answer: TRUE Objective: 20.6 Global Outcomes: GO2 17 Copyright © 2016 Pearson Education, Inc 20.5 Matching Questions Identify each of the designated regions on the energy diagram for the conversion of a substrate to product with and without an enzyme 1) energy of the substrate Answer: A Objective: 20.1 Global Outcomes: GO3 2) energy of the product Answer: D Objective: 20.1 Global Outcomes: GO3 3) activation energy without the enzyme Answer: B Objective: 20.1 Global Outcomes: GO3 4) activation energy with the enzyme Answer: C Objective: 20.1 Global Outcomes: GO3 18 Copyright © 2016 Pearson Education, Inc Match the correct term in enzyme action with each description A) coenzyme B) lock-and-key theory C) cofactor D) active site E) enzyme-substrate complex 5) the temporary combination of an enzyme with the compound on which it acts Objective: 20.1, 20.6 Global Outcomes: GO2 6) an organic compound that is sometimes needed to complete an enzyme Objective: 20.1, 20.6 Global Outcomes: GO2 7) the portion of an enzyme molecule where catalytic activity occurs Objective: 20.1, 20.6 Global Outcomes: GO2 8) an inorganic substance such as Mg2+ required by some enzymes for activity Objective: 20.1, 20.6 Global Outcomes: GO2 9) one theory that accounts for the unusual specificity of an enzyme Objective: 20.1, 20.6 Global Outcomes: GO2 Answers: 5) E 6) A 7) D 8) C 9) B 19 Copyright © 2016 Pearson Education, Inc Identify the effect of the following on the activity of maltase, an enzyme that hydrolyzes maltose A) decreases B) increases C) has no effect 10) decreasing the concentration of maltose Objective: 20.3 Global Outcomes: GO2 11) adjusting the temperature to the optimum temperature Objective: 20.3 Global Outcomes: GO2 12) raising the pH to 11.0 Objective: 20.3 Global Outcomes: GO2 13) increasing the concentration of maltase (enzyme) when the enzyme is saturated with substrate Objective: 20.3 Global Outcomes: GO2 14) lowering the pH to 1.0 Objective: 20.3 Global Outcomes: GO2 Answers: 10) A 11) B 12) A 13) B 14) A 20 Copyright © 2016 Pearson Education, Inc Identify the type of inhibition in each description A) competitive B) noncompetitive 15) an inhibitor that resembles the structure of the substrate Objective: 20.4 Global Outcomes: GO2 16) an inhibitor that forms a covalent bond with a side chain in the active site Objective: 20.4 Global Outcomes: GO2 17) Adding more substrate does not reverse the effect of this inhibitor Objective: 20.4 Global Outcomes: GO2 18) The inhibition can be reversed by increasing the concentration of substrate Objective: 20.4 Global Outcomes: GO2 19) The inhibitor does not resemble the substrate Objective: 20.4 Global Outcomes: GO2 Answers: 15) A 16) A 17) B 18) A 19) B 21 Copyright © 2016 Pearson Education, Inc Match the vitamin name with its corresponding chemical name A) thiamine B) cobalamin C) niacin D) cholecalciferol E) ascorbic acid F) riboflavin G) pyridoxine 20) vitamin B3 Objective: 20.6 Global Outcomes: GO2 21) vitamin B2 Objective: 20.6 Global Outcomes: GO2 22) vitamin B1 Objective: 20.6 Global Outcomes: GO2 23) vitamin C Objective: 20.6 Global Outcomes: GO2 24) vitamin B12 Objective: 20.6 Global Outcomes: GO2 25) vitamin B6 Objective: 20.6 Global Outcomes: GO2 Answers: 20) C 21) F 22) A 23) E 24) B 25) G 22 Copyright © 2016 Pearson Education, Inc ... Objective: 20. 3 Global Outcomes: GO2 24) "Physiological conditions" for reactions within the body are approximately A) pH and 37 °C B) pH and 37 °C C) pH and 37 °F D) pH and 273 °C E) pH and 273... pyridoxine 20) vitamin B3 Objective: 20. 6 Global Outcomes: GO2 21) vitamin B2 Objective: 20. 6 Global Outcomes: GO2 22) vitamin B1 Objective: 20. 6 Global Outcomes: GO2 23) vitamin C Objective: 20. 6... Objective: 20. 6 Global Outcomes: GO2 6) vitamin K Answer: fat soluble Objective: 20. 6 Global Outcomes: GO2 15 Copyright © 201 6 Pearson Education, Inc 7) niacin Answer: water soluble Objective: 20. 6