Chapter 8 Flashcards
laws derived from studies of physical properties of energy and how energy interacts with matter
laws of thermodynamics
energy available for performing work
free energy
reaction in which simple molecules are linked to form more complex molecules; requires input of energy
anabolic reaction
catabolic reaction
reaction in which molecules are broken down into simpler molecules; energy is released
systems biology
study of an organism as an integrated interacting system of genes, proteins, and biochemical reactions
total energy of a system
enthalpy
noncompetitive inhibitor
molecule that inhibits enzyme activity by binding to a site on an enzyme that is not the enzyme’s active site
exergonic reaction
reaction in which energy is released; ΔG is negative
reaction in which energy is released; ΔG is negative
exergonic reaction
enthalpy
total energy of a system
chemical equilibrium
state in a reversible reaction where no net change is present in concentrations of products/reactants
bioluminescence
production of light by an organism through biochemical reactions
anabolic reaction
reaction in which simple molecules are linked to form more complex molecules; requires input of energy
competitive inhibitor
molecule that bonds to the active site of an enzyme in order to inhibit the activity of the enzyme
endergonic reaction
reaction requiring energy; ΔG is positive
substrate
molecule(s) that bind to an enzyme during reaction catalysis
laws of thermodynamics
laws derived from studies of physical properties of energy and how energy interacts with matter
allosteric regulation
binding of an activator/inhibitor to a site other than the active site to regulate the activity of a protein
induced fit
due to the binding of a substrate, a change in an enzyme’s shape resulting in exposing the active site
free energy
energy available for performing work
state in a reversible reaction where no net change is present in concentrations of products/reactants
chemical equilibrium
molecule that inhibits enzyme activity by binding to a site on an enzyme that is not the enzyme’s active site
noncompetitive inhibitor
Which of the ofllowing is an example of an exergonic reaction?
A. The beating cilia of a protozoan
B. Cellular respiration
C. Phagocytosis
D. Receptor-mediated endocytosis
E. The Na+-K+ pump
B
A reaction that has a neghative ΔG
A. necessarily proceeds more rapidly than a reaction with a less negative ΔG.
B. is spontaneous.
C. cannot be used to drive a reaction with a positive ΔG.
D. is endergonic.
E. must have a negative change in enthalpy.
B
Enzymes are highly sensitive to pH and temperature because
A. changes in the environment raise their activation energy.
B. changes in temperature and pH readily break their hydrogen bonds.
C. of their 3D structure and side chains.
D. at extreme temperatures and pH levels, coenzymes add chemical groups to the substrate.
E. extremes of temperature and pH level change the ionization rate.
C
Which of the following statements about enzymes is false?
A. An enzyme changes shape when it binds to a substrate.
B. Enzymes lower the activation energy.
C. Enzymes are highly specific.
D. An enzyme may orient substrates, induce strain, or temperarily add chemical groups.
E. Most enzymes are much smaller than their substrates.
E
Allosteric Enzymes: Allosteric enzymes with multiple active sites differ from nonallosteric enzymes in that
A. allosteric enzymes are sensitive to inhibitors.
B. the dependence of allosteric enzyme activity on substrate concentration is sigmoid.
C. the activity of allosteric enzymes does not approach a maximum at high substrate concentration.
D. allosteric enzymes are made up of a single polypeptide chain.
E. nonallosteric enzymes regulate metabolism.
B
Enzyme Inhibitors: Which statement about enzyme inhibitors and inhibition is false?
A. Irreversible inhibitors can react with a functional group at an active site.
B. Noncompetitive inhibitors usually act by binding to the active site.
C. The extent of inhibition by a competitive inhibitor is dependent on the substrate concentration.
D. Irreversible inhibition of enzyme activity is rare in cells.
E. The structure of a competitive inhibitor of an enzyme resembles that of its substrate.
B
Enzyme Kinetics: Which of the following statements about the relationships shown in the graph is false?
A. The rate of an uncatalyzed reaction is determined by the concentration of the reactants.
B. In a catalyzed reaction, the reaction rate increases in a near linear fashion with substrate concentration at low substrate concentration.
C. The active site of an enzyme would be saturated with substrate at low substrate concentrations.
D. The maximum rate of enzyme-catalyzed reactions is a measure of the enzyme’s catalytic efficiency.
E. To obtain a curve as seen for the catalyzed reaction, the concentration of enzyme must be lower than substrate.
C
Water held back by a dam represents what kind of energy?
A. Hydroelectric
B. Irrigation
C. Potential
D. Kinetic
E. At times, all of the above
C
Enzyme Activity: Which of the following statements about the two reactions shown on the graph is false?
A. The catalyzed reaction has a lower ΔG.
B. The catalyzed reaction has a lower energy of activation.
C. The reaction will occur at a slower rate in the absence of a catalyst.
D. The products formed in the catalyzed and uncatalyzed reactions are identical.
E. The catalyzed reaction will reach equilibrium faster than the uncatalyzed reaction.
A
Reaction Rate vs. Thermodynamics: The rate of a chemical reaction depends on
A. ΔG.
B. enthalpy and entropy changes.
C. the activation energy.
D. the equilibrium concentrations of reactants and products.
E. whether the reaction is spontaneous or nonspontaneous.
C
activation energy
energy barrier existing to block tendency of the occurrence of a chemical reaction
Coupled Reactions II: ATP hydrolysis may be written as: ATP + H2O → ADP + Pi (reaction 1) and the phosphorylation of glucose by Pi: glucose + Pi → glucose 6-phosphate + H2O (reaction 2). Which statement about these two reactions is false?
A. Reaction 1 is exergonic.
B. The sum of reactions 1 and 2 is: ATP + glucose → ADP + glucose 6-phosphate (reaction 3).
C. Reaction 3 is endergonic.
D. Reaction 2 is endergonic.
E. Reaction 3 has a negative ΔG.
C
study of an organism as an integrated interacting system of genes, proteins, and biochemical reactions
systems biology
Coupled Reactions I: Complete the following sentence concerning the two coupled reactions shown here: ADP + Pi → ATP is an _______ reaction, ATP → ADP + Pi is an _______ reaction, and the conversion of ADP + Pi to ATP _______ energy.
A. exergonic; endergonic; releases
B. exergonic; endergonic; requires
C. endergonic; exergonic; releases
D. endergonic; exergonic; requires
E. exergonic; endergonic; does not involve
D
reaction in which molecules are broken down into simpler molecules; energy is released
catabolic reaction
ATP: This figure shows the molecule adenosine triphosphate, ATP. Which of the following statements regarding ATP is false
A. ATP is a monomer used in RNA synthesis.
B. Most of the energy stored in ATP is present in the P—O bonds.
C. The energy required to overcome the repulsion of adjacent phosphate groups during ATP formation is part of the source of ATP’s potential energy.
D. The hydrolysis of ATP is an exergonic reaction.
E. ATP is always hydrolyzed to ADP and Pi in cells.
E
Enzymes: This figure diagrammatically illustrates a generalized enzyme-catalyzed reaction. Which of the following statements regarding enzyme-catalyzed reactions is false?
A. Most enzymes are highly specific for a narrow range of substrates (reactants).
B. Enzymes remain chemically unchanged at the end of the catalytic cycle.
C. The enzyme–substrate complex (ES) can be held together via hydrogen bonding.
D. Enzymes do not chemically interact with the substrates, but can change their shape (induced fit).
E. Some enzymes can interact with more than one substrate at a time.
D
If ΔG for a reaction is positive, the reaction
A. is spontaneous.
B. could drive an energy-requiring process.
C. will necessarily have a positive ΔH.
D. will proceed quickly.
E. is endergonic.
E
pH and Enzymes: This figure shows the effect of pH on the activity of the enzymes pepsin, chymotrypsin, and arginase. Each enzyme has a different substrate. Consider a solution (solution 1) with equal concentrations of all three substrates for the three enzymes along with another solution (solution 2) containing all three enzymes. The fastest way to obtain a solution containing only pepsin substrate (removing the substrates for chymotrypsin and arginase) from solution 1 is to adjust the pH of solution 1 to _______ and add the enzyme solution (solution 2).
A. 2
B. 5
C. 7
D. 8
E. 10
D
Phosphorylation of ADP to ATP is endergonic, whereas the hydrolysis of ATP to ADP is exergonic. In cells, these reactions are:
A. in equilibrium.
B. endergonic overall.
C. kinetic.
D. balanced.
E. coupled.
E
An active site is
A. the part of the substrate that binds with an enzyme.
B. the part of the enzyme that binds with a substrate.C
C. the site where energy is added to an enzyme catalyst.
D. the site where enzymes are found in cells.
E. none of the above
B
Enzymes catalyze a reaction by ______ the substrates.
A. orienting
B. inducing strain in
C. adding chemical groups to
D. adding charges to
E. All of the above
E
A noncompetitive inhyibitor inhibits binding of a substrate to an enzyme by:
A. binding to the substrate.
B. binding to the active site.
C. lowering the activation energy.
D. increasing the ΔG of the reaction.
E. changing the shape of the active site.
E
Free Energy of Reactions II: Which of the following statements about the reaction shown in the accompanying figure is correct?
A. It has a negative ΔG.
B. It releases energy.
C. It is exergonic.
D. Given that ΔH for this reaction is zero, ΔS must be negative.
E. The amount of usable energy increases.
D
Free Energy of Reactions I: Select the pair of terms below that applies to the chemical reaction shown.
A. ΔG negative, exergonic
B. ΔG negative, endergonic
C. ΔG negative, equilibrium
D. ΔG positive, endergonic
E. ΔG positive, exergonic
A
Laws of Thermodynamics: The accompanying diagram represents the first law of thermodynamics. Which of the following statements regarding the first law of thermodynamics is false?
A. The total amount of energy before a transformation equals the total amount of energy after a transformation.
B. Energy is neither created nor destroyed during the energy transformation shown.
C. The energy transformation shown produces energy within a system.
D. The energy transformation shown can involve the conversion of potential energy into kinetic energy.
E. The energy transformation shown can involve the conversion of kinetic energy into potential energy.
C
Chemical Equilibrium: At the end of a chemical reaction (equilibrium) in which glucose 1-phosphate is converted to glucose 6-phosphate, there is 0.019 M glucose 6-phosphate and 0.001 M glucose 1-phosphate. The initial concentration of glucose 1-phosphate was 0.02 M and that of glucose 6-phosphate, 0. This reaction
A. is endergonic.
B. has a ΔG of zero at equilibrium.
C. has a positive ΔG.
D. runs (proceeds) to the left from the initial condition to equilibrium.
E. has a positive ΔH.
B
This figure shows the molecule adenosine triphosphate, ATP. Which of the following statements regardging ATP is false?
A. ATP is a monomer used in RNA synthesis.
B. Most of the energy stored in ATP is present in the P–O bonds.
C. The energy required to overcome the repulsion of adjacent phospate groups during ATP formation is part of the source ATP’s potential energy.
D. The hydrolysis of ATP is an exergonic reaction.
E. ATP holds most of its energy int he ribose sugar.
E
How does the second law of thermodynamics apply to organisms?
A. As energy transformations occur, free energy increases and unusable energy decreases.
B. To maintain order, life requries a constant input of energy.
C. The potential energy of ATP is converted to kinetic energy such as muscle contractions.
D. Reactions occur only with an input of energy.
E. It does not apply to organisms; the complexity of orgamisms contracics the second law.
B
Feedback Inhibition: The regulation of biochemical pathways in cells often occurs by _______ mechanisms, with the end product of the pathway acting as a(n) _______ of the enzyme that catalyzes the first step of the pathway.
A. irreversible; dead-end inhibitor
B. allosteric; competitive inhibitor
C. competitive; competitive inhibitor
D. allosteric; activator
E. allosteric; noncompetitive inhibitor
E
ATP can phosphorylate many different molecules. This means that ATP can
A. receive phosphate groups from those molecules.
B. donate phosphate groups to those molecules.
C. convert those molecules to phosphate groups.
D. receive the energy from those molecules.
E. all of the above
B
Which statement about thermodynamics is true?
A. Free energy is used up in an exergonic reaction.
B. Free energy cannot be used to do work.
C. The total amount of energy can change after a chemical transformation.
D. Free energy can be kinetic but not potential energy.
E. Entropy has a tendency to increase.
E
In a chemical reaction,
A. the rate depends on the value of ΔG.
B. the rate depends on the activation energy.
C. the entropy change depends on the activation energy.
D. the activation energy depends on the value of ΔG.
E. the change in free energy depends on the activation energy.
B
energy barrier existing to block tendency of the occurrence of a chemical reaction
activation energy
The molecule ATP is
A. a component of most proteins.
B. high in energy because of the presence of adenine.
C. required for many energy-transforming biochemical reactions.
D. a catalyst.
E. used in some exergonic reactions to provide energy.
C
natural disorder
entropy
In an enzyme-catalyzed reaction,
A. a substrate does not change.
B. the rate decreases as substrate concentration increases.
C. the enzyme can be permanently changed.
D. strain may be added to a substrate.
E. the rate is not affected by substrate concentration.
D
production of light by an organism through biochemical reactions
bioluminescence
Which statement about enzymes is not true?
A. They usually consist of proteins.
B. They change the rate of the catalyzed reaction.
C. They change the ΔG of the reaction.
D. They are sensitive to heat.
E. They are sensitive to pH.
C
molecule that bonds to the active site of an enzyme in order to inhibit the activity of the enzyme
competitive inhibitor
The active site of an enzyme
A. never changes shape.
B. forms no chemical bonds with substrates.
C. determines, by its structure, the specificity of the enzyme.
D. looks like a lump projecting from the surface of the enzyme.
E. changes the ΔG of the reaction.
C
due to the binding of a substrate, a change in an enzyme’s shape resulting in exposing the active site
induced fit
Coenzymes differ from enzymes in that coenzymes are
A. only active outside the cell.
B. polymers of amino acids.
C. smaller molecules, such as vitamins.
D. specific for one reaction.
E. always carriers of high-energy phosphate.
C
reaction requiring energy; ΔG is positive
endergonic reaction
Which statement about enzyme inhibitors is not true?
A. A competitive inhibitor binds the active site of the enzyme.
B. An allosteric inhibitor binds a site on the active form of the enzyme.
C. A noncompetitive inhibitor binds a site other than the active site.
D. Noncompetitive inhibition cannot be completely overcome by the addition of more substrate.
E. Competitive inhibition can be completely overcome by the addition of more substrate.
B
Which statement about temperature effects is not true?
A. Raising the temperature may reduce the activity of an enzyme.
B. Raising the temperature may increase the activity of an enzyme.
C. Raising the temperature may denature an enzyme.
D. Some enzymes are stable at the boiling point of water.
E. All enzymes have the same optimal temperature.
E
Which statement about the feedback inhibition of enzymes is not true?
A. It is usually exerted through allosteric effects.
B. It is directed at the enzyme that catalyzes the commitment step in a metabolic pathway.
C. It affects the rate of reaction, not the concentration of enzyme.
D. It acts by permanently modifying the active site.
E. It is an example of reversible inhibition.
D
molecule(s) that bind to an enzyme during reaction catalysis
substrate
binding of an activator/inhibitor to a site other than the active site to regulate the activity of a protein
allosteric regulation
entropy
natural disorder
