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.
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.
3) The formation of an enzyme-substrate complex is the ________ step in enzyme action.
A) first
B) second
C) third
D) fourth
E) last
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.
2
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.
6) Most enzymes are
A) fluid-mosaic proteins.
B) induced proteins.
C) substrate proteins.
D) fibrous proteins.
E) globular proteins.
7) In any reaction catalyzed by an enzyme, the reacting molecule is called the
A) substrate.
B) cofactor.
C) coenzyme.
D) isozyme.
E) allostere.
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.
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.
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.
E) hyperspecificity.
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.
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.
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.
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.
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.
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
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.
5
18) Creatine kinase can be used in the diagnosis of
A) hepatitis.
B) rickets.
C) heart attack.
D) prostatitis.
E) cancer.
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
20) To what main class of enzymes does the enzyme that catalyzes the following reaction belong?
O OH
|
CH3 C COO– → CH3 C HCOO–
A) oxidoreductase
B) transferase
C) hydrolase
D) lyase
E) isomerase
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
22) The hydrolysis of ester bonds in triglycerides is catalyzed by a(n)
A) lipase.
B) lyase.
C) isomerase.
D) hydrolase.
E) oxidoreductase.
23) The optimum temperature for sucrase activity is 37 °C. The hydrolysis of sucrose is slowest at which
temperature in the choices below?
A) 0 °C
B) 10 °C
C) 20 °C
D) 25 °C
E) 45 °C
24) “Physiological conditions” for reactions within the body are approximately
A) pH 3 and 37 °C.
B) pH 7 and 37 °C.
C) pH 7 and 37 °F.
D) pH 8 and 273 °C.
E) pH 7 and 273 K.
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.
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.
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.
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.
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.
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.
31) Pepsinogen is an example of a(n)
A) coenzyme.
B) cofactor.
C) isoenzyme.
D) allosteric enzyme.
E) zymogen.
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.
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.
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.
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.
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.
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.
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.
39) Some insecticides kill insects by inhibiting the enzyme
A) alcohol dehydrogenase.
B) acetylcholinesterase.
C) creatine kinase.
D) lipase.
E) penicillinase.
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.
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.
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.
43) Pepsinogen is an example of a(n)
A) coenzyme.
B) cofactor.
C) isoenzyme.
D) allosteric enzyme.
E) zymogen.
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.
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.