enzyme review

inactive precursor of an enzyme

Zymogen

In which of the following pairs of terms do the two terms have the same meaning? a. holoenzyme and conjugated enzyme b. coenzyme and simple enzyme c. apoenzyme and cofactor d. more than one correct response e. no correct response

a

(1) A substrate is the substance upon which an enzyme "acts." (2) Competitive enzyme inhibition is a reversible process. (3) Vitamin C is necessary for the formation of the structural protein collagen.

a. All three statements are true.

(1) All of the B vitamins are water-soluble. (2) The induced-fit model for enzyme action allows for small changes in active-site geometry. (3) Noncompetitive enzyme inhibitors bind to an enzyme at sites other than the active site.

a. All three statements are true.

(1) The enzyme lactase catalyzes the hydrolysis of lactose. (2) The spent form of vitamin E is regenerated by vitamin C. (3) All coenzymes are cofactors but not all cofactors are coenzymes.

a. All three statements are true.

component of all conjugated enzymes

apoenzyme/cofactor

(1) Activation of a zymogen produces a proteolytic enzyme. (2) An enzyme-substrate complex is the final product in most enzyme-catalyzed reactions. (3) Three forms of vitamin A are active in the human body.

b. Two of the three statements are true.

(1) An apoenzyme, by itself, has no biochemical activity. (2) Urease is an example of an enzyme with absolute specificity. (3) All enzymes have names that end in -ase.

b. Two of the three statements are true.

An enzyme active site is the location in an enzyme where substrate molecules a. are made unreactive b. become catalysts c. undergo change d. more than one correct response e. no correct response

c

In which of the following pairs of substances are both members of the pair zymogens? a. pepsin and pepsinogen b. proelastase and elastase c. prothrombin and pepsinogen d. more than one correct response e. no correct response

c

Which of the following B vitamins has a structure in which a metal atom is present? a. folate b. biotin c. vitamin B12 d. more than one correct response e. no correct response

c

(1) The primary function of vitamin D in the body is that of an antioxidant. (2) Holoenzymes are conjugated enzymes. (3) An increase in enzyme activity is always associated with an increase in the temperature of an enzyme-containing system.

c. Only one of the statements is true.

component of some conjugated enzymes

coenzyme

Which of the following binds to an enzyme at its active site? a. irreversible inhibitor b. reversible competitive inhibitor c. reversible noncompetitive inhibitor d. more than one correct response e. no correct response

d

Which of the following could be a component of a conjugated enzyme? a. coenzyme b. cofactor c. apoenzyme d. more than one correct response e. no correct response

d

Which of the following is not a water-soluble vitamin? a. vitamin C b. vitamin A c. vitamin D d. more than one correct response e. no correct response

d

Which of the following statements about a competitive inhibitor is correct? a. It must resemble the substrate in general shape. b. Its effect can be diminished by increasing substrate concentration. c. It simultaneously occupies the active site along with the normal substrate. d. More than one correct response. e. No correct response.

d

Which of the following statements concerning sources for B vitamins is correct? a. Most fruits are poor sources. b. Most vegetables are good sources. c. Meat and dairy products are good sources. d. More than one correct response. e. No correct response.

d

(1) The active site of an enzyme always contains one or more metal atoms. (2) The water-soluble vitamins are the B vitamins and vitamins A and C. (3) An enzyme's turnover number is the rate at which it is degraded and resynthesized within the human body.

d. None of the statements are true.

has both protein and nonprotein parts

holoenzyme

The final product of a series of enzyme-catalyzed reactions causes the enzyme that catalyzes the first reaction of the series to be inhibited. This is an example of a. positive regulator control b. substrate control c. feedback control d. competitive control

C

What is the function of enzymes within living systems? a. structural elements b. neurotransmitters c. catalysts d. hormones

C

A plot of enzyme activity (y-axis) versus pH (x-axis) with other variables constant is a a. straight line with an upward slope b. line with an upward slope and a long flat top c. line with an upward slope followed by a downward slope d. straight horizontal line

C

An enzyme active site is the location in the enzyme where: a. The actual catalysis occurs. b. The side groups of the protein interact with the catalyst. c. The catalyst creates the substrate molecules. d. The substrate molecules are created.

A

The protein portion of a conjugated enzyme is called a(n). a. apoenzyme b. coenzyme c. holoenzyme d. cofactor

A

Vitamins C and E are important, respectively, in a. bone formation and antioxidant activity b. bone formation and proper use of calcium and phosphorus c. vision and blood clotting d. vision and proper use of calcium and phosphorus

A

Which of the following is always present in both conjugated enzymes and simple enzymes? a. Protein b. a vitamin c. a cofactor d. a coenzyme

A

Enzymes have names that a. always end with -ise b. always end with -in c. can end with either -ase or -in d. can end with either -ase or -ogen

C

Which of the following statements concerning a competitive enzyme inhibitor is correct? a. It resembles the substrate in charge distribution. b. It forms a strong covalent bond to an amino acid side-chain group at a site other than the active site. c. Its effect is never reversible. d. Its effect can be overcome by increasing the inhibitor concentration.

A

A plot of enzyme activity (y-axis) versus substrate concentration (x-axis) with other variables constant is a a. straight line with an upward slope b. line with an upward slope and a long flat top c. line with an upward slope followed by a downward slope d. straight horizontal line

B

The major function for B vitamins within the human body is as a. antioxidants b. components of coenzymes c. regulators of cell differentiation d. regulators of calcium ion and phosphate ion concentrations in blood

B

The number of known vitamins is a. 10 b. 13 c. 15 d. 20

B

Which of the following enzyme properties is explained by the lock-and-key model for enzyme action? a. high turnover rate b. absolute specificity c. susceptibility to denaturation d. susceptibility to deactivation

B

An enzyme that catalyzes the oxidation of only one kind of alcohol would be described as showing a. group specificity b. stereochemical specificity c. linkage specificity d. absolute specificity

D

In which of the following is the pairing between enzyme type and enzyme function incorrect? a. carbohydrases - hydrolysis of glycosidic bonds in carbohydrates b. oxidase - oxidation of a substrate c. mutase - conversion of one structural isomer into another d. hydrogenase - removal of water from substrate

D

In which of the following pairs of vitamins are both members of the pair water-soluble? a. vitamin E and thiamin b. vitamin A and vitamin K c. vitamin E and vitamin B6 d. niacin and pantothenic acid =

D

Which of the following binds to an enzyme at a location other than the active site? a. substrate b. irreversible inhibitor c. reversible competitive inhibitor d. reversible noncompetitive inhibitor

D

Which of the following statements concerning enzyme active sites is incorrect? a. They generally involve only a small portion of the enzyme. b. Noncompetitive inhibitors can change active site shape. c. The lock-and-key model of enzyme activity assumes that an active site has a fixed, rigid geometrical conformation. d. More than one correct response. e. No correct response.

e

Which of the following statements concerning the effect of temperature change on an enzyme-catalyzed reaction is incorrect? a. An increase in temperature can stop the reaction by denaturing the enzyme. b. An increase in temperature can increase the reaction rate by increasing the speed at which molecules move. c. An increase in temperature to the optimum temperature maximizes reaction rate. d. More than one correct response. e. No correct response.

e

Conversion of a D isomer to the L isomer

isomerase

Removal of CO2 from a substrate

lyase

Introduction of a double bond by removal of hydrogen from a substrate

oxidoreductase

Transfer of a phosphate group between substances

transferase

Transfer of an amino group between substrates

transferase