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Enzyme Practice Problems
These problems have been adapted from Mr. Buckely. We thank him for his hard work.
Choose the answer which BEST completes the following statements or answers the
following questions. Circle the number of the answer which is correct.
1. An enzymatic reaction that occurs at 5. In negative feedback mechanisms,
20 C would be expected to double its when excess metabolic end products fill
rate at a minimum temperature of allosteric enzyme sites
(1.) 21 C (2.) 30 C (3.) 40 C (4.) 10 C (1.) more enzymes are created
(2.) the metabolic reaction is halted
2. A substrate can not bind to an (3.) they behave as
enzyme if the enzyme has activating modulators
(1.) an attached cofactor (4.) metabolic activity is increased
(2.) a competitive inhibitor in its active (5.) the enzymes are denatured
site
(3.) an activating modulator in its 6. According to the induced-fit
allosteric site hypothesis, the active site of an enzyme
(4.) an attached coenzyme (1.) is rigid and inflexible
(5.) all of the previous (2.) is precisely tailored to fit a substrate
perfectly
3. Noncompetitive inhibitors render the (3.) may change its shape to fit any
enzyme helpless by substrate
(1.) altering their shape, making their (4.) binds to any substrate
active site inoperable (5.) fits a specific substrate
(2.) binding to their proposed substrate imperfectly, creating a stressed
(3.) filling their active site situation
(4.) denaturing their proposed
substrate 7. Enzymes accelerate biochemical
(5.) destroying their allosteric sites reactions by
(1.) raising the energy of activation
4. Under what conditions will an (2.) altering the direction of the
allosteric enzyme bind to a substrate? reaction
(1.) when an inhibitor binds to its active (3.) raising cellular temperatures
site (4.) changing equilibrium
(2.) when an activating modulator binds concentrations
to its allosteric site (5.) lowering activation energy
(3.) when an activating modulator binds
to its active site 8. Cyanide bonds easily to the metallic
(4.) whenever their is sufficient portion of cytochrome molecules
substrate (respiratory enzymes). Which concept
(5.) when any modulator joins its active does this most directly illustrate?
site (1.) steric hindrance
(2.) competitive inhibition
(3.) induced fit
(4.) noncompetitive inhibition
(5.) entropy 11. The part of an enzyme that is used
to break down or construct molecules is
Base your answers to questions 9 and known as the active
10 below on the reading (1.) structure (2.) complex (3.)
passage that follows and your site (4.) zone
knowledge of biology.
A student ground 1 gram of fresh 12. When enzymes are heated above a
liver in a mortar, placed the ground liver certain temperature, what process do
in a test tube, and added 1 ml of they undergo?
peroxide. The gas that was generated (1.) Disintegration (2.) Desiccation (3.)
was collected. A glowing splint Petrification (4.) Denaturation
burst into flames when placed in the
gas. The student then repeated 13. The molecules that enzymes
the procedure, using one gram of boiled combine with and convert into other
liver and one gram of liver treated with molecules are (1.) Bile Salts (2.)
a strong acid. When peroxide was Catalysts (3.) Indicators (4.)
added to each sample of liver, no gas Products (5.)Substrates
was generated.
14. Enzymes have a distinct advantage
9. The gas that was generated was most over nonbiological catalysts because
likely they:
(1.) oxygen (1.) Are made of protein (2.) Are very
(2.) nitrogen efficient, specific, and sensitive to
(3.) carbon dioxide control
(4.) hydrogen (3.) Are all allosteric (4.) Can not be
(5.) ammonia denatured by heating
(6.) water vapor
15. Most coenzymes may be included in
10. If the substance in the liver that classes of foodstuffs known as:
acted on the peroxide was an enzyme, it (1.) Minerals (2.) Carbohydrates (3.)
could Fats (4.) Vitamins (5.) Metallic ions
(1.) be recovered from the living tissue
that had not been boiled or treated with 16. Which statement about enzyme
acid after the reaction ceased catalyzed reactions is NOT true?
(2.) not be recovered because it was (1.) enzymes form complexes with
consumed while engaging in its catalytic their substrates.
reaction (2.) enzymes lower the activation
activities energy for chemical reactions.
(3.) not be recovered because there is (3.) enzymes change the heat of
no enzyme in liver that catalyzes the reaction for chemical reactions.
breakdown of peroxide (4.) many enzymes change shape
(4.) not be recovered because grinding slightly when substrate binds.
would break up the molecule (5.) reactions occur at the "active
(5.) be recovered only before the site" of enzymes, where a
peroxide was added precise 3D orientation of amino
acids is an important feature (2.) a competitive inhibitor in its active
of catalysis. site
(3.) an activating modulator in its
17. Enzymes: allosteric site
(1.) are composed primarily of (4.) an attached coenzyme
polypeptides, which are polymers of (5.) all of the previous
amino acids.
(2.) can bind prosthetic groups such as 21. Competitive inhibitors render the
metal ions that participate in enzyme enzyme helpless by
reactions. (1.) lowering its activation energy
(3.) have defined structures. (2.) binding to their proposed substrate
(4.) bind their substrates at active sites. (3.) filling their active site
(5.) all of the previous statements are (4.) denaturing their proposed
true. substrate
(5.) destroying their allosteric sites
18. In the graph below showing
reaction rate vs. substrate 22. Noncompetitive inhibitors render
concentration, the reason that the curve the enzyme helpless by
reaches a plateau, and does not (1.) altering their shape, making their
increase any further at high substrate active site inoperable
concentration is that: (2.) binding to their proposed substrate
(3.) filling their active site
(4.) denaturing their proposed
substrate
(5.) destroying their allosteric sites
23. In negative feedback mechanisms,
when excess metabolic end products fill
(1.) the active site is saturated with allosteric enzyme sites
substrate (1.) more enzymes are created
(2.) there is a competitive inhibitor (2.) the metabolic reaction is halted
present (3.) they behave as activating
(3.) there is a non-competitive inhibitor modulators
present (4.) metabolic activity is increased
(4.) the allosteric enzyme is locked in an (5.) the enzymes are denatured
inactive conformation
19. An enzymatic reaction that 24. According to the induced-fit
occurs at 20 C would be expected to hypothesis, the active site of
quadruple its rate at a minimum an enzyme
temperature of (1.) is rigid and inflexible
(1.) 21 C (2.) 30 C (3.) 40 C (4.) 10 (2.) is precisely tailored to fit a substrate
C perfectly
(3.) may change its shape to fit any
20. A substrate cannot bind to an substrate
enzyme is because the enzyme has (4.) binds to any substrate
(1.) an attached cofactor
(5.) fits a specific substrate molecules (respiratory enzymes). This
imperfectly, creating a stressed reaction tends to be irreversible. Which
situation concept does this most directly
illustrate?
25. Activation energy is (1.) steric hindrance
(1.) energy that must be added to get a (2.) competitive inhibition
reaction started, which is recovered as (3.) induced fit
the reaction proceeds (4.) noncompetitive inhibition
(2.) difference in energy between (5.) entropy
reactants and products
(3.) energy that is lost as heat 29. An enzyme
(4.) free energy (1.) is a source of energy for endergonic
(5.) equal to the entropy times the reactions
absolute temperature (2.) is an organic catalyst
(3.) increases the EA of a reaction
26. In the presence of alcohol (4.) is a inorganic catalyst
dehydrogenase, the rate of reduction of (5.) can bind to nearly any molecule
acetaldehyde to ethanol increases as
you increase the concentration of 30. What name is given to the
acetaldehyde. Eventually the rate of the reactants in an enzymatically catalyzed
reaction reaches a maximum, where reaction?
further increases in the concentration of (1.) EA
acetaldehyde have no effect. Why? (2.) products
(1.) all of the alcohol dehydrogenase (3.) active sites
molecules are bound to acetaldehyde (4.) reactors
molecules (2.) at high concentrations of (5.) substrate
acetaldehyde, the activation energy of 31. As a result of its involvement in a
the reaction decreases reaction, an enzyme
(3.) the enzyme is no longer specific for (1.) loses a phosphate group
acetaldehyde (2.) permanently alters its shape.
(4.) at high concentrations of (3.) loses energy
acetaldehyde, the change in free energy (4.) is unchanged
of the reaction decreases (5.) is used up
27. The result of a(n) __________ 32. What will sulfuric acid (H2SO4) do
reaction is that energy is released. to most enzymes?
Energy must be added for a(n) (1.) It is the substrate on which
__________ reaction to proceed. catalase acts.
(1.) enzyme catalyzed, non-spontaneous (2.) It binds with hydrogen peroxide
(2.) exergonic, endergonic during titration.
(3.) endergonic, spontaneous (3.) It accelerates the reaction
(4.) catalytic, non-catalytic between enzyme and substrate.
(5.) oxidative, hydrolysis (4.) It blocks the active site of the
enzyme.
28. Many heavy metals bond easily to (5.) It denatures the enzyme by
the metallic portion of cytochrome altering the active site.
acetylcholine hydrolysis is
33. The inactive form of an enzyme, decreased. Subsequent addition of
such as pepsinogen is referred to as more acetylcholine restores the original
(1.) a coenzyme rate of acetylcholine hydrolysis. Which
(2.) a zymogen statement correctly explains this
(3.) an allosteric enzyme observation?
(4.) a cofactor (1.) Succinylcholine must be a
competitive inhibitor with
34. The binding of an allosteric acetylcholine. (2.) Succinylcholine must
inhibitor to an enzyme causes the rate be an allosteric regulator for this
of product formation by the enzyme to enzyme.
decrease. Which best explains why this (3.) The active site must have the wrong
decrease occurs? configuration to permit succinylcholine
(1.) The allosteric inhibitor binds to the binding.
active site, preventing the substrate (4.) Succinylcholine must be a non-
from binding. competitive inhibitor.
(2.) The allosteric inhibitor causes free (5.) The activation energy barrier for
energy change of the reaction to succinylcholine hydrolysis is higher than
increase. for acetylcholine hydrolysis.
(3.) The allosteric inhibitor causes a
structural change in the enzyme that 36. Enzyme activity is affected by pH
prevents the substrate from binding at because
the active site. (1.) most substrates don't function well
(4.) The allosteric inhibitor lowers the at high or low pH
temperature of the active site. (2.) high or low pH may disrupt
(5.) The allosteric inhibitor binds to hydrogen bonding or ionic interactions
the substrate and prevents it from and thus change the shape of the active
binding at the active site. site
(3.) low pH will denature all enzymes
35. Succinylcholine is structurally (4.) changes in pH can cause loss of
almost identical to acetylcholine. If cofactors from the enzyme
succinylcholine is added to a mixture (5.) the binding of hydrogen ions to the
that contains acetylcholine and the enzyme absorbs energy and thus there
enzyme that hydrolyzes acetylcholine may not be enough energy to overcome
(but not succinylcholine), the rate of the activation energy barrier
Correctly complete the following statements.
1. _______________ is the energy needed to start
a chemical reaction.
2. The substrate bonds to a specific area on the enzyme
molecule known as the enzyme's _______________.
3. Compounds similar in shape to an enzyme's substrate,
that can compete with the substrate molecules by
binding with the active site of the enzyme are said
to be _______________.
4. ____________________ enzymes often change their shape when a
molecule binds to a part of the enzyme away from the active site.
5. An inactive form of an enzyme is called a(n) _____________________.
Don’t forget to do the essay questions below.
Essays:
1. Compare the lock and key theory of enzyme-substrate interaction,
to the induced fit concept of enzyme function.
2. Discuss HOW the following factors influence the activity of MOST
human enzymes and EXPLAIN WHY they have this influence:
a.) increased substrate concentration in a fixed amount of enzyme
b.) pH shifts
c.) temperature shifts including 0 C, 20 C, 37 C, and 60 C
d.) competitive inhibition
e.) allosteric inhibition