An important group of peripheral membrane proteins are enzymes such
as the phospholipases that cleave the head groups of phospholipids.
What properties must these enzymes exhibit?
A) resistance to degradation B) independence from
cofactor interaction C) water solubility D) lipid
solubility E) membrane-spanning domains
Water Solubility
Which curve(s) on the graphs may represent the temperature and pH
profiles of an enzyme taken from a bacterium that lives in a mildly
alkaline hot springs at temperatures of 70�C or higher?
A) curves 1 and 5 B) curves 2 and 4 C)
curves 2 and 5 D) curves 3 and 4 E) curves 3 and
5
Curves 3 and 5
Succinate dehydrogenase catalyzes the conversion of succinate to
fumarate. The reaction is inhibited by malonic acid, which resembles
succinate but cannot be acted upon by succinate dehydrogenase.
Increasing the ratio of succinate to malonic acid reduces the
inhibitory effect of malonic acid.
What is malonic acid's role with respect to succinate dehydrogenase?
A) It is a competitive inhibitor. B) It blocks the
binding of fumarate. C) It is a noncompetitive
inhibitor. D) It is able to bind to succinate. E) It
is an allosteric regulator.
Competitive Inhibitor
In experimental tests of enzyme evolution, where a gene encoding an
enzyme is subjected to multiple cycles of random mutagenesis and
selection for altered substrate specificity, the resulting enzyme had
multiple amino acid changes associated with altered substrate
specificity. Where in the enzyme were these amino acid changes located?
A) only in the active site B) only in the active
site or near the active site C) in or near the active site
and at surface sites away from the active site D) only at
surface sites away from the active site E) only in the
hydrophobic interior of the folded protein
in or near the active site and at surface sites away from the active site
A series of enzymes catalyze the reaction X ? Y ? Z ? A. Product A
binds to the enzyme that converts X to Y at a position remote from its
active site. This binding decreases the activity of the enzyme.
What is substance X?
A) a coenzyme B) an allosteric inhibitor
C) a substrate D) an intermediate E) the
product
A substrate
Which of the following statements is true about enzyme-catalyzed reactions?
A) The reaction is faster than the same reaction.
B) The free energy change of the reaction is opposite from the
reaction that occurs in the absence of the enzyme. C) The
reaction always goes in the direction toward chemical
equilibrium. D) Enzyme-catalyzed reactions require energy
to activate the enzyme. E) Enzyme-catalyzed reactions
release more free energy than noncatalyzed reactions
The reaction is faster than the same reaction in the absence of the enzyme.
How might an amino acid change at a site distant from the active site
of the enzyme alter the enzyme's substrate specificity?
A) by changing the enzyme's stability B) by
changing the enzyme's location in the cell C) by changing
the shape of the protein D) by changing the enzyme's pH
optimum E) an amino acid change away from the active site
cannot alter the enzyme's substrate specificity
by changing the shape of the protein
Zinc, an essential trace element for most organisms, is present in
the active site of the enzyme carboxypeptidase. The zinc most likely
functions as a(n)
A) competitive inhibitor of the enzyme. B)
noncompetitive inhibitor of the enzyme. C) allosteric
activator of the enzyme. D) cofactor necessary for enzyme
activity. E) coenzyme derived from a vitamin.
cofactor necessary for enzyme activity
When ATP releases some energy, it also releases inorganic phosphate.
What purpose does this serve (if any) in the cell?
A) The phosphate is released as an excretory waste.
B) The phosphate can only be used to regenerate more ATP.
C) The phosphate can be added to water and excreted as a
liquid. D) The phosphate may be incorporated into any
molecule that contains phosphate. E) It enters the nucleus
to affect gene expression.
The phosphate may be incorporated into any molecule that contains phosphate.
A solution of starch at room temperature does not readily decompose
to form a solution of simple sugars because
A) the starch solution has less free energy than the sugar
solution. B) the hydrolysis of starch to sugar is
endergonic. C) the activation energy barrier for this
reaction cannot be surmounted. D) starch cannot be
hydrolyzed in the presence of so much water. E) starch
hydrolysis is nonspontaneous
the activation energy barrier for this reaction cannot be surmounted.
Chemical equilibrium is relatively rare in living cells. Which of the
following could be an example of a reaction at chemical equilibrium in
a cell?
A) a reaction in which the free energy at equilibrium is
higher than the energy content at any point away from
equilibrium B) a chemical reaction in which the entropy
change in the reaction is just balanced by an opposite entropy
change in the cell's surroundings C) an endergonic reaction
in an active metabolic pathway where the energy for that reaction is
supplied only by heat from the environment D) a chemical
reaction in which both the reactants and products are not being
produced or used in any active metabolic pathway E) no
possibility of having chemical equilibrium in any living cell
a chemical reaction in which both the reactants and products are not
being produced or used in any active metabolic pathway
Which of the following statements regarding enzymes is true?
A) Enzymes increase the rate of a reaction by making the
reaction more exergonic. B) Enzymes increase the rate of a
reaction by lowering the activation energy barrier. C)
Enzymes increase the rate of a reaction by reducing the rate of
reverse reactions. D) Enzymes change the equilibrium point
of the reactions they catalyze. E) Enzymes make the rate of
a reaction independent of substrate concentrations.
Enzymes increase the rate of a reaction by lowering the activation
energy barrier.
For the hydrolysis of ATP to ADP + Pi, the free energy change is -7.3
kcal/mol under standard conditions (1 M concentration of both
reactants and products). In the cellular environment, however, the
free energy change is about -13 kcal/mol. What can we conclude about
the free energy change for the formation of ATP from ADP and Pi under
cellular conditions?
A) It is +7.3 kcal/mol. B) It is less than +7.3
kcal/mol. C) It is about +13 kcal/mol. D) It is
greater than +13 kcal/mol. E) The information given is
insufficient to deduce the free energy change.
It is about +13 kcal/mol.
According to the induced fit hypothesis of enzyme catalysis, which of
the following is correct?
A) The binding of the substrate depends on the shape of the
active site. B) Some enzymes change their structure when
activators bind to the enzyme. C) A competitive inhibitor
can outcompete the substrate for the active site. D) The
binding of the substrate changes the shape of the enzyme's active
site. E) The active site creates a microenvironment ideal for
the reaction.
The binding of the substrate changes the shape of the enzyme's active site.
ncreasing the substrate concentration in an enzymatic reaction could
overcome which of the following?
A) denaturization of the enzyme B) allosteric
inhibition C) competitive inhibition D) saturation
of the enzyme activity E) insufficient cofactors
competitive inhibition
During a laboratory experiment, you discover that an enzyme-catalyzed
reaction has a ?G of -20 kcal/mol. If you double the amount of enzyme
in the reaction, what will be the ?G for the new reaction?
kcal/mo-20 l
If an enzyme in solution is saturated with substrate, the most
effective way to obtain a faster yield of products is to
A) add more of the enzyme. B) heat the solution to
90�C. C) add more substrate. D) add an allosteric
inhibitor. E) add a noncompetitive inhibitor.
add more of the enzyme.
How do cells use the ATP cycle shown in the figure?
A) Cells use the cycle to recycle ADP and phosphate.
B) Cells use the cycle to recycle energy released by ATP
hydrolysis. C) Cells use the cycle to recycle ADP, phosphate,
and the energy released by ATP hydrolysis. D) Cells use the
cycle to generate or consume water molecules as needed. E)
Cells use the cycle primarily to generate heat.
Cells use the cycle to recycle ADP and phosphate.
Which of the following best describes enthalpy (H)?
A) the total kinetic energy of a system B) the heat
content of a chemical system C) the system's entropy
D) the cell's energy equilibrium E) the condition of a
cell that is not able to react
the heat content of a chemical system
Allosteric enzyme regulation is usually associated with
A) lack of cooperativity. B) feedback
inhibition. C) activating activity. D) an enzyme
with more than one subunit. E) the need for cofactors.
an enzyme with more than one subunit.
Some bacteria are metabolically active in hot springs because
A) they are able to maintain a lower internal
temperature. B) high temperatures make catalysis
unnecessary. C) their enzymes have high optimal
temperatures. D) their enzymes are completely insensitive to
temperature. E) they use molecules other than proteins or
RNAs as their main catalysts.
their enzymes have high optimal temperatures.
A chemical reaction that has a positive ?G is correctly described as
A) endergonic. B) endothermic. C)
enthalpic. D) spontaneous. E) exothermic.
Endergonic
Why is ATP an important molecule in metabolism?
A) Its hydrolysis provides an input of free energy for
exergonic reactions. B) It provides energy coupling between
exergonic and endergonic reactions. C) Its terminal
phosphate group contains a strong covalent bond that, when
hydrolyzed, releases free energy. D) Its terminal phosphate
bond has higher energy than the other two. E) It is one of
the four building blocks for DNA synthesis.
It provides energy coupling between exergonic and endergonic reactions.
A series of enzymes catalyze the reaction X ? Y ? Z ? A. Product A
binds to the enzyme that converts X to Y at a position remote from its
active site. This binding decreases the activity of the enzyme.
With respect to the enzyme that converts X to Y, substance A
functions as
A) a coenzyme. B) an allosteric inhibitor.
C) the substrate. D) an intermediate. E) a
competitive inhibitor.
an allosteric inhibitor.
Mutations that result in single amino acid substitutions in an enzyme
A) can have no effect on the activity or properties of the
enzyme. B) will almost always destroy the activity of the
enzyme. C) will often cause a change in the substrate
specificity of the enzyme. D) may affect the
physicochemical properties of the enzyme such as its optimal
temperature and pH. E) may, in rare cases, cause the enzyme
to run reactions in reverse.
may affect the physicochemical properties of the enzyme such as its
optimal temperature and pH.
Which of the following statements is true about enzyme-catalyzed reactions?
A) The reaction is faster than the same reaction in the
absence of the enzyme. B) The free energy change of the
reaction is opposite from the reaction that occurs in the absence of
the enzyme. C) The reaction always goes in the direction
toward chemical equilibrium. D) Enzyme-catalyzed reactions
require energy to activate the enzyme. E) Enzyme-catalyzed
reactions release more free energy than noncatalyzed reactions.
The reaction is faster than the same reaction in the absence of the enzyme.
What is the difference (if any) between the structure of ATP and the
structure of the precursor of the A nucleotide in RNA?
A) The sugar molecule is different. B) The
nitrogen-containing base is different. C) The number of
phosphates is three instead of one. D) The number of
phosphates is three instead of two. E) There is no
difference.
There is no difference.
Which of the following metabolic processes can occur without a net
influx of energy from some other process?
A) ADP + Pi ? ATP + H?O B) C?H??O? + 6 O? ? 6 CO? + 6
H?O C) 6 CO? + 6 H?O ? C?H??O? + 6 O? D) amino acids
? protein E) glucose + fructose ? sucrose
C?H??O? + 6 O? ? 6 CO? + 6 H?O
Some of the drugs used to treat HIV patients are competitive
inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the
high mutation rate of HIV means that the virus rapidly acquires
mutations with amino acid changes that make them resistant to these
competitive inhibitors. Where in the reverse transcriptase enzyme
would such amino acid changes most likely occur in drug-resistant viruses?
A) in or near the active site B) at an allosteric
site C) at a cofactor binding site D) in regions of
the protein that determine packaging into the virus capsid
E) such mutations could occur anywhere with equal
probability
in or near the active site
When chemical, transport, or mechanical work is done by an organism,
what happens to the heat generated?
A) It is used to power yet more cellular work. B) It
is used to store energy as more ATP. C) It is used to
generate ADP from nucleotide precursors. D) It is lost to
the environment. E) It is transported to specific organs
such as the brain.
It is lost to the environment.
Which of the following statements describes enzyme cooperativity?
A) A multienzyme complex contains all the enzymes of a
metabolic pathway. B) A product of a pathway serves as a
competitive inhibitor of an early enzyme in the pathway. C)
A substrate molecule bound to an active site of one subunit promotes
substrate binding to the active site of other subunits. D)
Several substrate molecules can be catalyzed by the same
enzyme. E) A substrate binds to an active site and inhibits
cooperation between enzymes in a pathway.
A substrate molecule bound to an active site of one subunit promotes
substrate binding to the active site of other subunits.
Which of the following statements is true concerning catabolic pathways?
A) They combine molecules into more energy-rich
molecules. B) They supply energy, primarily in the form of
ATP, for the cell's work. C) They are endergonic.
D) They are spontaneous and do not need enzyme catalysis.
E) They build up complex molecules such as protein from simpler
compounds.
They supply energy, primarily in the form of ATP, for the cell's work
The active site of an enzyme is the region that
A) binds allosteric regulators of the enzyme. B) is
involved in the catalytic reaction of the enzyme. C) binds
noncompetitive inhibitors of the enzyme. D) is inhibited by
the presence of a coenzyme or a cofactor.
is involved in the catalytic reaction of the enzyme.
Protein kinases are enzymes that transfer the terminal phosphate from
ATP to an amino acid residue on the target protein. Many are located
on the plasma membrane as integral membrane proteins or peripheral
membrane proteins. What purpose may be served by their plasma membrane localization?
A) ATP is more abundant near the plasma membrane. B)
They can more readily encounter and phosphorylate other membrane
proteins. C) Membrane localization lowers the activation
energy of the phosphorylation reaction. D) They flip back
and forth across the membrane to access target proteins on either
side. E) They require phospholipids as a cofactor.
They can more readily encounter and phosphorylate other membrane proteins.