Deck 19: Enzymes

Question 1

The rate of an enzyme-catalyzed reaction initially increases with an increase in the substrate concentration,but eventually reaches a maximum value,even though the concentration of substrate continues to increase.Which of the following best explains why?

A)As substrate concentration increases,the substrates preferentially bind with each other instead of the active site of the enzyme,and no additional catalysis occurs.
B)As substrate concentration increases,the active sites of all the enzyme molecules become occupied with substrate molecules,and no additional binding can occur.
C)An increase in substrate concentration eventually increases the temperature of the reaction mixture,and the enzyme becomes denatured.
D)An increase in substrate concentration allows for greater competition between substrate and inhibitor binding,and enzyme activity ceases.
E)When substrate concentrations become too high,local variations of pH occur that cause the enzyme to become denatured.

Answer 1

As substrate concentration increases,the active sites of all the enzyme molecules become occupied with substrate molecules,and no additional binding can occur.

Question 2

The enzyme acetylcholinesterase catalyzes the hydrolysis of acetylcholine.Which of the following is a product of this hydrolysis reaction?

A)

B)

C)

D)

E)

Answer 2

Question 3

Trypsin is a protease enzyme that cleaves peptide bonds on the carbonyl side of basic amino acids.Which labeled bond(s)in the peptide below would be cleaved by trypsin?

A)A
B)B
C)C
D)D
E)A,C,and D

Answer 3

C

Question 4

Acetylcholine is a neurotransmitter that transmits a signal from a nerve cell to a muscle cell,causing the muscle to contract.How is the neurotransmitter inactivated so that the muscle can relax?

A)It is denatured by the local pH and loses its active conformation.
B)It is hydrolyzed by the enzyme acetylcholinesterase.
C)It is taken up and stored by the muscle cells.
D)It is dissolved in the blood and is transported through the circulatory system.
E)All of the choices are correct.

Question 5

Sucrase is an example of an enzyme that displays absolute specificity.What does the term "absolute specificity" indicate about an enzyme?

A)It catalyzes the reaction of only a single substrate.
B)It catalyzes the reaction of only one class of compounds.
C)It catalyzes one type of reaction for the same class of compounds.
D)It catalyzes the reaction of only a single enantiomer of a compound.
E)It catalyzes the reaction of only a single type of bond.

Question 6

Proteolytic digestive enzymes are often produced in an inactive form.What is the name that refers to the inactive form of an enzyme?

A)isozyme
B)zwitterion
C)proenzyme
D)inhibitor
E)allele

Question 7

Proteases,or proteolytic enzymes,are responsible for which of the following functions?

A)formation of the zwitterion form of a protein
B)hydrolysis of the ester bonds in dietary triglycerides
C)hydrolysis of the peptide bonds between amino acids in proteins
D)formation of the glycosidic linkages in disaccharides and polysaccharides
E)formation of bacterial cell walls

Question 8

The protease enzyme chymotrypsin cleaves peptide bonds on the carbonyl side of aromatic amino acids.Which labeled bond in the peptide below would be cleaved by chymotrypsin?

A)A
B)B
C)C
D)D
E)E

Question 9

What is an allosteric enzyme?

A)an enzyme whose activity is regulated by the binding of a small effector molecule
B)the inactive form of an enzyme
C)an enzyme that has become denatured and can no longer catalyze reactions
D)an enzyme that is bound to an inhibitor molecule
E)an enzyme that catalyzes reactions in plants and animals,but not humans

Question 10

Which of the following describes how an enzyme can affect the transition state in an enzyme-catalyzed reaction?

A)modifying the local pH by accepting or donating H⁺ ions
B)placing stress on a bond in the substrate,making it easier to break
C)bringing two reactants together in close proximity and in a suitable orientation for reaction
D)None of the choices are correct.
E)All of the choices are correct.

Question 11

What term describes the pH at which an individual enzyme functions best?

A)isoelectric pH
B)pH optimum
C)physiological pH
D)neutral pH
E)zwitterion pH

Question 12

The pancreatic enzymes trypsin,chymotrypsin,and elastase all hydrolyze peptide bonds on the carbonyl side of several different amino acids in a protein.What term best describes their enzyme specificity?

A)stereospecific
B)peptide
C)absolute
D)linkage
E)group

Question 13

The diagram below shows the energy pathway of an uncatalyzed reaction.How does the energy diagram change when an enzyme is used in the same reaction?

A)The energy of the products decreases.
B)The energy of the reactants increases.
C)The energy of the reactants decreases.
D)The activation energy decreases.
E)The energy of the reactants becomes equal to the energy of the products.

Question 14

In feedback inhibition of an enzyme-catalyzed biosynthetic pathway,what frequently serves as the negative allosteric effector?

A)the starting material of the pathway
B)acetylcholine
C)oxygen
D)the final product of the pathway
E)temperature

Question 15

Which of the following statements concerning enzymes is FALSE?

A)Enzymes are the body's biological catalysts,increasing the rate of cellular reactions.
B)Enzymes are usually globular proteins with flexible three-dimensional shapes.
C)The reactant in an enzyme-catalyzed reaction is called a cofactor.
D)The active site of an enzyme is where substrate binding and catalysis occur.
E)Inhibitors are molecules that cause an enzyme to lose its activity.

Question 16

About half of the 223 amino acids in the enzyme trypsin are hydrophobic.Where in the tertiary structure of this globular protein are these amino acids most likely to be found?

A)at the N-terminal end of the protein chain
B)at the C-terminal end of the protein chain
C)on the exterior surface of the folded protein
D)in the interior of the folded protein
E)in the active site of the enzyme

Question 17

What three structurally similar pancreatic serine proteases function to cleave certain peptide bonds in proteins?

A)pepsinogen,zymogen,and acetylcholinesterase
B)pepsinogen,trypsin,and pepsin
C)tryptophan,trypsin,and chymotrypsin
D)trypsin,chymotrypsin,and elastase
E)choline,tryptophan,and proline

Question 18

Elastase is a protease enzyme that cleaves peptide bonds on the carbonyl side of the amino acids glycine and alanine.What products result from treatment of a peptide with the primary structure shown below with elastase? Pro-Gly-Phe-Ala

A)the individual amino acids proline,glycine,phenylalanine,and alanine
B)Pro-Gly,phenylalanine,and alanine
C)proline,Gly-Phe,and alanine
D)Pro-Gly,and Phe-Ala
E)proline,glycine,and Phe-Ala

Question 19

Which of the following correctly describes pepsinogen?

A)It is the inactive form of the enzyme pepsin.
B)It is the cofactor for the enzyme pepsin.
C)It is the inhibitor of the enzyme pepsin.
D)It is an isoenzyme of pepsin.
E)It is the name of the reaction catalyzed by pepsin.

Question 20

Which of the following best describes the type of binding between an irreversible inhibitor and an enzyme?

A)weak
B)non-covalent
C)hydrogen bonding
D)hydrophobic interactions
E)very tight

Question 21

Which of the following is a medical use of enzymes?

A)enzyme assays to diagnose damage or disease to a particular organ or tissues
B)injection of enzymes to counteract blood clots
C)enzyme replacement therapy for missing or malfunctioning enzymes
D)analytical reagents in the clinic laboratory
E)All of the choices are correct.

Question 22

The graph shows how the rate of an enzyme-catalyzed reaction depends on the variable x.Which of the following quantities could x most likely represent?

A)enzyme concentration
B)pH
C)energy
D)substrate concentration
E)progress of reaction

Question 23

For enzyme-catalyzed reactions,what happens as the concentration of the substrate is increased?

A)The rate continues to increase as substrate concentration increases.
B)The rate increases until it reaches a maximum,constant value.
C)The rate increases until it reaches a maximum,then the rate decreases.
D)The rate decreases with increasing concentration of the substrate.
E)The rate decreases until it reaches a minimum,constant value.

Question 24

An enzyme catalyzes the removal of an amino group from one substrate and its addition to another compound.To what class of enzymes does it belong?

A)kinase
B)hydrolase
C)transferase
D)oxidoreductase
E)lyase

Question 25

What is the water-soluble vitamin from which NAD⁺ is made?

A)riboflavin (B₂)
B)niacin (B₃)
C)pyridoxine (B₆)
D)cyanocobalamine (B₁₂)
E)riboflavin (B₂)and niacin (B₃)are correct.

Question 26

Which of the following is NOT a class of enzymes?

A)isomerases
B)transferases
C)carnases
D)lyases
E)ligases

Question 27

To which class of enzymes does an enzyme belong if it catalyzes the rearrangement of functional groups within a molecule?

A)oxidoreductases
B)lyases
C)ligases
D)isomerases
E)lyases and ligases are correct.

Question 28

Lactase is an enzyme that catalyzes the following reaction.Which statement describing this reaction is FALSE?

A)Lactose is the substrate in this reaction.
B)Glucose is a product in this reaction.
C)Galactose is a cofactor in this reaction.
D)This reaction occurs in the active site of lactase.
E)Lactase is a hydrolase enzyme.

Question 29

What parameter of a reaction does an enzyme alter?

A)product structure
B)activation energy
C)pH
D)temperature
E)concentration

Question 30

Which class of enzymes catalyzes reactions involving the formation of double bonds?

A)elastases
B)oxidoreductases
C)lyases
D)catalases
E)isomerases

Question 31

To which class of enzymes would you assign an enzyme that carries out the dehydrogenation of its substrate?

A)oxidoreductases
B)transferases
C)lyases
D)hydrolases
E)All of the choices are correct.

Question 32

What type of specificity is displayed by an enzyme that is able to catalyze a reaction of D-glucose,but not L-glucose?

A)absolute specificity
B)stereospecificity
C)group specificity
D)optical specificity
E)sugar specificity

Question 33

What class of enzymes catalyzes the following reaction?

A)hydrogenase
B)catalase
C)isomerase
D)elastase
E)lipase

Question 34

Carboxypetidase A is a highly folded,globular protein that functions as a protease enzyme.Which of the following is a likely assumption about the amino acid residues that exist on the exterior of this folded protein?

A)The majority of these amino acids have disulfide bonds between cysteine residues.
B)The majority of these amino acids are hydrophilic in nature.
C)The majority of these residues are glycine.
D)None of these residues is serine.
E)The majority of these residues are nonpolar in nature.

Question 35

What is the effect of an enzyme on the equilibrium constant for the reaction it catalyzes?

A)It increases the equilibrium constant.
B)It decreases the equilibrium constant.
C)It may increase or decrease the equilibrium constant,depending upon the specific reaction.
D)It makes the equilibrium constant numerically equal to the reaction rate.
E)It has no effect on the equilibrium constant.

Question 36

Phenylketonuria (PKU)is an inherited disease caused by the inability to produce a properly working form of the enzyme phenylalanine hydroxylase.This enzyme catalyzes the conversion of the amino acid phenylalanine to the amino acid tyrosine by adding a hydroxyl group to the para position on the ring.Based on this information,what is the structure of tyrosine (Tyr)?

A)

B)

C)

D)

E)

Question 37

What portion of an enzyme is in direct contact with the substrate?

A)the inert site
B)the alpha site
C)the beta site
D)the delta site
E)the active site

Question 38

At extremes of pH,an enzyme will lose its biologically active conformation.What term describes the state of the enzyme under these conditions?

A)denatured
B)acidic
C)basic
D)buffered
E)noncovalent

Question 39

What is the classification of an enzyme that catalyzes the joining of two molecules?

A)kinase
B)ligase
C)oxidoreductase
D)transferase
E)hydrolase

Question 40

What is the first step in an enzyme-catalyzed reaction?

A)catalysis of enzyme
B)dimerizing the substrate
C)ionization of enzyme
D)decrease of pH
E)formation of an enzyme-substrate complex

Question 41

What type of enzyme regulation occurs when the final product of a pathway shuts off the entire pathway for its own synthesis?

A)irreversible inhibition
B)competitive inhibition
C)feedback inhibition
D)poisoning
E)noncompetitive inhibition

Question 42

Which statement concerning an enzyme is true?

A)An enzyme increases the size of the equilibrium constant of the reaction it catalyzes.
B)An enzyme decreases the size of the equilibrium constant of the reaction it catalyzes.
C)An enzyme shifts the equilibrium so that more product is formed when equilibrium is reached.
D)An enzyme increases the rate of a chemical reaction by lowering the activation energy.
E)An enzyme slows down reactions that occur too rapidly to be effective in the body.

Question 43

Many enzymes are regulated by having more than one binding site.What is the term used to describe these enzymes?

A)allosteric enzymes
B)lipases
C)proenzymes
D)lyases
E)isomerases

Question 44

In 1956,Christian de Duve discovered organelles in the cytoplasm of certain cells that have hydrolytic enzymes that destroy bacteria and viruses.What are these organelles called?

A)lysosomes
B)mitochondria
C)endosomes
D)ribosomes
E)nucleosomes

Question 45

Some enzymes require an additional nonprotein prosthetic group in order to function.What is the protein part of this combination called?

A)substrate
B)apoenzyme
C)effector
D)cofactor
E)holoenzyme

Question 46

The arrival of a nerve impulse at the end plate of the nerve axon results in an influx of what ion?

A)calcium
B)sodium
C)potassium
D)bicarbonate
E)phosphate

Question 47

The graph shows how the rate of an enzyme-catalyzed reaction depends on the variable x.Which of the following quantities could x most likely represent?

A)enzyme concentration
B)energy
C)temperature
D)substrate concentration
E)progress of reaction

Question 48

A holoenzyme is a functional enzyme composed of what two parts?

A)apoenzyme and cofactor
B)amino acid and NAD⁺
C)substrate and catalyst
D)transferase and ligase
E)substrate and inhibitor

Question 49

The enzyme hexokinase catalyzes the phosphorylation of glucose according to the reaction shown below.Glucosamine is a competitive inhibitor of hexokinase.Which of the following best describes the inhibition by glucosamine?

A)Glucosamine stabilizes the active site of the enzyme,preventing glucose-6-phosphate from being released.
B)Glucosamine reacts with glucose,preventing it from binding to the active site of the enzyme.
C)Glucosamine binds to the active site of the enzyme,preventing glucose from binding.
D)Glucosamine binds to the surface of the enzyme,causing a change in the shape of both the enzyme and the active site,preventing glucose from binding.
E)Glucosamine reacts with glucose-6-phosphate,preventing it from being released from the active site.

Question 50

HIV protease inhibitors block the activity of enzymes responsible for which of the following?

A)viral replication
B)digestion
C)oxygen transport
D)antibiotic activity
E)pain production

Question 51

What is the function of a lyase enzyme?

A)to catalyze redox reactions
B)to catalyze the transfer of a functional group from one molecule to another
C)to catalyze hydrolysis reactions
D)to catalyze the addition of a group to a double bond or the removal of a group to form a double bond
E)to catalyze the formation or cleavage of a C-C,C-S,C-O,or C-N bond

Question 52

Most cellular enzymes work optimally at what pH?

A)2
B)5
C)7
D)9
E)12

Question 53

A second binding site on an allosteric enzyme has the ability to bind to a molecule that alters the shape of the active site.What is this second site called?

A)structural analog binding site
B)effector binding site
C)feedback binding site
D)coenzyme binding site
E)cofactor binding site

Question 54

Of the following types of molecular interactions,which is NOT likely to be involved in the binding of an enzyme to a substrate?

A)covalent linkages
B)hydrogen bonds
C)van der Waals attractions
D)polar-polar attractions
E)ionic attractions

Question 55

What term refers to an organic molecule that binds transiently to an enzyme and participates in the reaction by either accepting or donating a chemical group?

A)apoenzyme
B)cofactor
C)effector
D)coenzyme
E)analog

Question 56

The penicillin class of antibiotics is inhibitors of an enzyme responsible for the formation of bacterial cell walls.The penicillin covalently binds to a serine residue in the active site of the enzyme,as depicted below.What type of bond is formed between the penicillin and the active site?

A)hydrogen bond
B)ionic bond
C)glycosidic linkage
D)ester bond
E)acetal bond

Question 57

Some enzymes require an additional nonprotein prosthetic group in order to function.What is the nonprotein part of this combination called?

A)apoenzyme
B)effector
C)mineral
D)cofactor
E)vitamin

Question 58

The enzyme fumarase is a lyase enzyme that catalyzes the hydration of fumarate to give malate.What is the structure of malate?

A)

B)

C)

D)

E)

Question 59

Which of the following is true for an enzyme catalyzed reaction?

A)The rate of the reaction will increase indefinitely with an increase in the substrate concentration.
B)The rate of the reaction will increase with an increase in the substrate concentration until it reaches a maximum rate.
C)The rate of the reaction will decrease as the substrate concentration increases.
D)The rate of the reaction is unaffected by substrate concentration.
E)The rate of the reaction decreases as the amount of enzyme available increases.

Question 60

What is the term for a molecule that is similar in structure and charge distribution to the substrate in an enzyme-catalyzed reaction?

A)effector
B)transition state
C)structural analog
D)irreversible inhibitor
E)noncompetitive inhibitor

Question 61

The presence of an enzyme will alter the relative ratio of product to reactant for a biochemical reaction.

Question 62

Chymotrypsin catalyzes the hydrolysis of dietary carbohydrates.

Question 63

Irreversible inhibitors bind very tightly,and sometimes covalently,to enzymes.

Question 64

The presence of an enzyme catalyst will affect the time taken for a reaction to reach equilibrium.

Question 65

The vitamin biotin is a component of a coenzyme.

Question 66

Which of the following describes the function of the enzyme cis-trans isomerase?

A)It breaks the double bond in an unsaturated fatty acid.
B)It converts pentose sugars to hexose sugars.
C)It converts between isomers on a disubstituted benzene ring.
D)It converts between the boat and chair conformations of a cyclohexane.
E)It breaks and re-forms a double bond to change the arrangement of the groups around a double bond.

Question 67

Binding of a negative effector converts an active site on an enzyme into the active configuration.

Question 68

The rates of enzyme-catalyzed reactions increase with increasing pH.

Question 69

Many enzymes are destroyed if the temperature rises significantly above 37ºC.

Question 70

Which of the following will NOT destroy an enzyme by denaturation?

A)increase in temperature above 37°C (body temperature)
B)decrease in temperature below 37°C
C)significant increase in pH
D)significant decrease in pH
E)All of the choices will destroy an enzyme.

Question 71

A proenzyme is an inactive form of an enzyme.

Question 72

Arsenic is an example of an irreversible enzyme inhibitor.

Question 73

Isomerases rearrange the functional groups within a molecule.

Question 74

Hydrochloric acid in the stomach is partially responsible for activating pepsinogen.