Chapter 6 Energy ATP Enzymes
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.
A
In addition to regulating enzymes with activators and inhibitors, cells also regulate enzyme activity by A) restricting enzymes to specific organelles or membranes. B) limiting the availability of substrates. C) covalently bonding enzymes into large aggregates. D) secreting enzymes out of the cell.
A
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 enzyme that determine packaging into the virus capsid
A
What is the role of malonic acid with respect to succinate dehydrogenase? A) It is a noncompetitive inhibitor. B) It is a competitive inhibitor. C) It blocks the binding of fumarate. D) It is an allosteric regulator.
A
Which of the following is a statement of the first law of thermodynamics? A) Energy cannot be created or destroyed. B) The entropy of the universe is decreasing. C) The entropy of the universe is constant. D) Energy cannot be transferred or transformed.
A
) 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 chemical reaction in which the free energy at equilibrium is higher than the free-energy content at any point away from equilibrium B) a chemical reaction in which neither the reactants nor the products are being produced or used in any other active metabolic pathway at that time in the cell C) an endergonic reaction in an active metabolic pathway in which the energy for that reaction is supplied only by heat from the environment D) Chemical equilibrium is not possible under any circumstances in a living cell.
B
) Which of the following is true for all exergonic reactions? A) The products have more total energy than the reactants. B) The reaction proceeds with a net release of free energy. C) The reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted to reactants. D) A net input of energy from the surroundings is required for the reaction to proceed.
B
A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases, although they don't often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then which of the following is the most likely mechanism by which the muscle cell ATPase maintains intracellular calcium concentrations? A) The ATPase pumps calcium from the outside of the cell into the SR against the concentration gradient. B) The ATPase pumps calcium from the cytosol into the SR against the concentration gradient. C) The ATPase transfers ℗i to calcium ions so that they may diffuse into the SR. D) The ATPase opens a calcium ion channel that allows calcium ions to diffuse back into the SR along the concentration gradient
B
A severe fever can result in death if not brought under control because A) it may destroy the primary structure of cellular enzymes. B) it may alter the tertiary structure of cellular enzymes. C) it may increase the rate of cellular chemical reactions. D) it may result in binding inappropriate substrates by cellular enzymes.
B
ATP hydrolysis in a test tube releases only about half as much energy as ATP hydrolysis in the cell. Which of the following is the best explanation for this observation? A) Cells maintain higher internal pressure, which speeds up the reaction rate. B) ATP hydrolysis in a test tube occurs under standard conditions; in the cell, reactant and product concentrations differ from standard conditions. C) ATP hydrolysis in a cell produces different products than ATP hydrolysis in a test tube. D) ATP hydrolysis in cells is catalyzed by enzymes, which releases more energy than the uncatalyzed reaction in a test tube.
B
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ________ is to ________. A) exergonic; spontaneous B) exergonic; endergonic C) free energy; entropy D) work; energy
B
Hydrolysis of ATP releases energy, which results in the production of ADP and inorganic phosphate. What is commonly the ultimate fate of inorganic phosphate produced in the cytosol? A) It is secreted as waste. B) It is combined with ADP to regenerate ATP. C) It is phosphorylated. D) It is hydrolyzed to release additional energy.
B
The active site of an enzyme is the region that A) binds allosteric regulators of the enzyme. B) binds substrates for the enzyme. C) binds noncompetitive inhibitors of the enzyme. D) is inhibited by the presence of a coenzyme or a cofactor.
B
The ∆G for a particular enzyme-catalyzed reaction is -20 kcal/mol. If the amount of enzyme in the reaction is doubled, what will be the ∆G for the new reaction? A) -40 kcal/mol B) -20 kcal/mol C) 0 kcal/mol D) +20 kcal/mol E) +40 kcal/mol
B
The ∆G for a particular enzyme-catalyzed reaction is -20 kcal/mol. If the enzyme is removed, what will be the ∆G for the noncatalyzed reaction? A) -40 kcal/mol B) -20 kcal/mol C) 0 kcal/mol D) +20 kcal/mol E) +40 kcal/mol
B
Under a particular set of conditions in the lab, the enzyme in a chemical reaction is saturated. Which of the following alterations to the reaction will increase the rate at which substrate is converted to product? A) increasing the concentration of substrate in the reaction B) increasing the amount of enzyme in the reaction C) increasing the volume of the reaction without increasing the amount of substrate or enzyme D) decreasing the concentration of product in the reaction
B
Which of the following is an example of cooperativity? A) binding of an ATP molecule along with another substrate in an active site B) binding of a molecule to one subunit of a tetramer, which promotes faster binding to each of the other three subunits C) the product of one enzyme in a metabolic pathway serving as the substrate for the next enzyme in the pathway D) binding of the end product of a metabolic pathway to the enzyme that catalyzes the first step in the pathway
B
Which of the following metabolic processes can occur without a net influx of energy from some other process? A) ADP + <IMG/>i → ATP + H2O B) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O C) 6 CO2 + 6 H2O → C6H12O6 + 6 O2 D) amino acids → protein
B
Which of the following reactions tend to require an input of energy? A) exergonic B) dehydration C) hydrolysis D) catabolic
B
Which of the following statements about enzyme-catalyzed reactions is true? A) The free-energy change of the reaction is greater than when the same reaction occurs in the absence of an enzyme. B) The rate of the reaction is greater than when the same reaction occurs in the absence of an enzyme. C) Enzymes always drive reactions toward chemical equilibrium. D) Energy from ATP is required to activate the enzyme before it can catalyze the reaction.
B
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.
B
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.
B
A mutation that results in a single amino acid substitution in the active site of an enzyme A) may alter the ability of a noncompetitive inhibitor to bind to the enzyme. B) may alter the ability of an allosteric regulator to alter enzyme activity. C) may change the substrate specificity of the enzyme. D) may alter the ∆G for the reaction catalyzed by the enzyme.
C
A noncompetitive inhibitor decreases the rate of an enzymatic reaction by A) binding to the active site of the enzyme. B) changing the ∆G for the reaction. C) changing the shape of the enzyme active site. D) decreasing the activation energy required for the reaction.
C
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 easily be surmounted at room temperature. D) starch cannot be hydrolyzed in the presence of so much water. E) starch hydrolysis is nonspontaneous.
C
ATP is an example of which of the following? A) a pentose sugar B) a DNA nucleotide C) an RNA nucleotide D) an amino acid with three phosphate groups attached
C
An aminoacyl-tRNA synthetase is the enzyme that catalyzes the attachment of a particular amino acid to its corresponding tRNA. This reaction requires energy from ATP. The enzyme initially binds the amino acid and ATP, but it is unable to bind the tRNA. Which of the following would be a likely mechanism by which the enzyme ultimately binds the tRNA and attaches the amino acid? A) Transfer of the ATP to the tRNA opens the active site to allow the tRNA to bind. B) Hydrolysis of ATP activates the amino acid, which is released, opening up the active site to allow binding of the tRNA. C) Hydrolysis of ATP phosphorylates the amino acid and results in a conformational change in the active site, which allows the tRNA to bind. D) Alteration in the conformation of the tRNA allows it to bind to the active site along with the amino acid and ATP.
C
For the hydrolysis of ATP to ADP + ℗i, the free-energy change is -7.3 kcal/mol under standard conditions (1 Mconcentration 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 ℗i 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 about +26 kcal/mol.
C
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? A) denaturation of the enzyme B) allosteric inhibition C) competitive inhibition D) saturation of the enzyme activity
C
Most cells cannot harness heat to perform work because A) heat does not involve a transfer of energy. B) cells do not have much heat; they are relatively cool. C) temperature is usually uniform throughout a cell. D) heat can never be used to do work
C
Please use the following information to answer the question(s) below. 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. 2) Based on this information, which of the following is correct? A) Succinate dehydrogenase is the enzyme, and fumarate is the substrate. B) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate. C) Succinate is the substrate, and fumarate is the product. D) Fumarate is the product, and malonic acid is a noncompetitive inhibitor. E) Malonic acid is the product, and fumarate is a competitive inhibitor.
C
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.
C
The cellular process of synthesizing large molecules from smaller ones is defined as A) catalysis. B) metabolism. C) anabolism. D) dehydration. E) catabolism
C
The induced fit model of enzyme activity suggests which of the following? A) The binding of substrate depends on the conformation of the active site. B) The binding of an activator alter the conformation of the active site to bind products more tightly. C) The binding of substrate changes the conformation of the active site to bind substrate more tightly. D) The binding of a competitive inhibitor changes the shape of the active site to bind substrate less tightly.
C
Which of the following is true for anabolic pathways? A) They do not depend on enzymes. B) They are usually spontaneous chemical reactions. C) They consume energy to build polymers from monomers. D) They release energy as they degrade polymers to monomers
C
) Hydrolysis of ATP releases energy, which results in the production of ADP and inorganic phosphate. What is commonly the immediate fate of the inorganic phosphate in the cell? A) It is secreted as waste. B) It is phosphorylated. C) It is hydrolyzed to release additional energy. D) It is used to form a phosphorylated intermediate.
D
A mutation that results in a single amino acid substitution in a region of the enzyme outside of the active site A) may alter the ability of a competitive inhibitor to bind to the enzyme. B) will almost always destroy the activity of the enzyme. C) will often change the substrate specificity of the enzyme. D) may alter the optimal pH for the enzyme
D
Alteration of an amino acid at a site distant from the active site of an enzyme may alter the substrate specificity of the enzyme by A) changing the optimum pH for the enzyme. B) changing the intracellular location of the enzyme. C) changing the binding site for an allosteric regulator. D) changing the conformation of the enzyme
D
Cooperativity is a form of allosteric activation in which A) the product of a metabolic pathway serves as a competitive inhibitor of an early enzyme in the pathway. B) all of the enzymes in a metabolic pathway are contained within a single multienzyme complex. C) completion of one step in a metabolic pathway is required before a subsequent step can occur. D) binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits.
D
If an enzyme is added to a solution in which its substrate and product are in equilibrium, what will occur? A) Additional product will be formed. B) The reaction will change from endergonic to exergonic. C) The free energy of the system will change. D) Nothing; the reaction will stay at equilibrium
D
In experimental tests of enzyme evolution, a gene encoding an enzyme was subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity. The resulting enzyme had altered substrate specificity and multiple amino acid changes. Where in the enzyme would you expect these amino acid changes to be located? A) only in or near the active site B) only in the hydrophobic interior of the folded protein C) only at surface sites distant from the active site D) in or near the active site and at surface sites distant from the active site
D
In most exergonic reactions, the reactants capable of interacting to form products typically must first overcome a thermodynamic barrier known as the A) entropy of the reaction. B) energy conservation of the reaction. C) chemical equilibrium of the reaction. D) activation energy of the reaction.
D
Increasing the enzyme concentration in an enzymatic reaction could overcome which of the following? A) denaturation of the enzyme B) allosteric inhibition C) competitive inhibition D) saturation of the enzyme activity
D
Please use the following information to answer the question(s) below. A series of enzymes catalyze the reactions illustrated in the following metabolic pathway: 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) an intermediate D) a substrate
D
The mechanism by which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as A) metabolic inhibition. B) noncooperative inhibition. C) irreversible inhibition. D) feedback inhibition.
D
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 in the form of ATP. C) It is used to synthesize ADP. D) It is released to the environment.
D
Which of the following describes the critical role that ATP plays in cellular metabolism? A) The terminal phosphate group of ATP is attached by a particularly strong covalent bond that releases extra energy when broken. B) It is one of the four building blocks for RNA synthesis. C) Hydrolysis of ATP provides energy to drive exergonic reactions in the cell. D) ATP serves as an energy shuttle in the cell, coupling exergonic and endergonic reactions.
D
Which of the following is an exergonic reaction? A) synthesis of ATP from ADP and ℗i B) a dehydration reaction between two monosaccharides to produce a disaccharide C) formation of a peptide bond D) hydrolysis of glycogen to release glucose monomers
D
Which of the following is true of enzymes? A) Nonprotein cofactors alter the substrate specificity of enzymes. B) Enzyme function is increased if the 3-D structure or conformation of an enzyme is altered. C) Enzyme function is independent of physical and chemical environmental factors such as pH and temperature. D) Enzymes increase the rate of chemical reaction by lowering activation energy barriers. E) Enzymes increase the rate of chemical reaction by providing activation energy to the substrate.
D
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.
D
1) The cellular process of breaking down large molecules into smaller ones is defined as A) catalysis. B) metabolism. C) anabolism. D) dehydration. E) catabolism.
E
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.
E
