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General, Organic, and Biological Chemistry, 4e (Timberlake)
Chapter 20 Enzymes and Vitamins
20.1 Multiple-Choice Questions
- 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.
Global Outcomes: GO
- Which of the following is NOT a step in the enzyme-catalyzed conversion of a substrate to
product?
A) The substrate changes its shape so it can bind at 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
1
- 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.
Global Outcomes: GO
- The enzymes that extract energy from biomolecules for our use are located in the
A) plasma.
B) cell mitochondria.
C) lymph.
D) urine.
E) lipoproteins.
Answer: B
Objective: 20.
Global Outcomes: GO
- Most enzymes are
A) fluid-mosaic proteins.
B) induced proteins.
C) substrate proteins.
D) fibrous proteins.
E) globular proteins.
Answer: E
Objective: 20.
Global Outcomes: GO
- 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.
Global Outcomes: GO
2
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
4
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- Creatine kinase can be used in the diagnosis of
A) hepatitis.
B) rickets.
C) heart attack.
D) prostatitis.
E) cancer.
Answer: C
Objective: 20.
Global Outcomes: GO
- 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.
Global Outcomes: GO
5
- 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
Answer: A
Objective: 20.
Global Outcomes: GO
- "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.
Answer: B
Objective: 20.
Global Outcomes: GO
- "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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
7
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
8
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- Some insecticides kill insects by inhibiting the enzyme
A) alcohol dehydrogenase.
B) acetylcholinesterase.
C) creatine kinase.
D) lipase.
E) penicillinase.
Answer: B
Objective: 20.
Global Outcomes: GO
- 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.
Global Outcomes: GO
10
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- Pepsinogen is an example of a(n)
A) coenzyme.
B) cofactor.
C) isoenzyme.
D) allosteric enzyme.
E) zymogen.
Answer: E
Objective: 20.
Global Outcomes: GO
- 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.
Global Outcomes: GO
11
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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
Objective: 20.
Global Outcomes: GO
13
20.2 Bimodal Questions
- A biological catalyst is called a(n) __________.
A) lipid
B) enzyme
C) cofactor
D) coenzyme
E) substrate
Answer: B
Objective: 20.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
14
- 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.
Global Outcomes: GO
- 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.
Global Outcomes: GO
20.3 Short Answer Questions
Indicate whether each of the following is fat soluble or water soluble.
- vitamin B 6
Answer: water soluble
Objective: 20.
Global Outcomes: GO
- vitamin A
Answer: fat soluble
Objective: 20.
Global Outcomes: GO
- pantothenic acid
Answer: water soluble
Objective: 20.
Global Outcomes: GO
- ascorbic acid
Answer: water soluble
Objective: 20.
Global Outcomes: GO
16
- vitamin E
Answer: fat soluble
Objective: 20.
Global Outcomes: GO
- vitamin K
Answer: fat soluble
Objective: 20.
Global Outcomes: GO
- niacin
Answer: water soluble
Objective: 20.
Global Outcomes: GO
- folic acid
Answer: water soluble
Objective: 20.
Global Outcomes: GO
- vitamin D
Answer: fat soluble
Objective: 20.
Global Outcomes: GO
- riboflavin
Answer: water soluble
Objective: 20.
Global Outcomes: GO
20.4 True/False Questions
- Enzymes always require a cofactor.
Answer: FALSE
Objective: 20.
Global Outcomes: GO
- Alanine transaminase is an example of a transferase enzyme.
Answer: TRUE
Objective: 20.
Global Outcomes: GO
- Pyruvate carboxylase is an example of a ligase enzyme.
Answer: TRUE
Objective: 20.
Global Outcomes: GO
17
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.
- energy of the substrate
Answer: A
Objective: 20.
Global Outcomes: GO
- energy of the product
Answer: D
Objective: 20.
Global Outcomes: GO
- activation energy without the enzyme
Answer: B
Objective: 20.
Global Outcomes: GO
- activation energy with the enzyme
Answer: C
Objective: 20.
Global Outcomes: GO
19
Match the correct term in enzyme action with each description.
A) cofactor
B) lock-and-key theory
C) enzyme-substrate complex
D) active site
E) coenzyme
- the temporary combination of an enzyme with the compound on which it acts
Objective: 20.1, 20.
Global Outcomes: GO
- an organic compound that is sometimes needed to complete an enzyme
Objective: 20.1, 20.
Global Outcomes: GO
- the portion of an enzyme molecule where catalytic activity occurs
Objective: 20.1, 20.
Global Outcomes: GO
- an inorganic substance such as Mg
required by some enzymes for activity
Objective: 20.1, 20.
Global Outcomes: GO
- one theory that accounts for the unusual specificity of an enzyme
Objective: 20.1, 20.
Global Outcomes: GO
Answers: 5) C 6) E 7) D 8) A 9) B
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