Quiz 6

During a laboratory experiment you discover that an enzyme-catalyzed reaction has a delta G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the delta G for the new reaction? a. +40 kcal/mole b. +20 kcal/mole c. -20 kcal/mole d. -40 kcal/mole

-20 kcal/mole

How can one increase the rate of a chemical reaction? a. Increase the entropy of the reactants. b. Increase the activation energy needed. c. Add a catalyst d. Cool the reactants.

add a catalyst

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. add a noncompetitive inhibitor. c. add more substrate. d. heat the solution to 90°C.

add more of the enzyme

Kinases are enzymes that catalyze phosphorylation (the addition of a phosphate group) whereas phosphatases are enzymes that catalyze the removal of phosphate groups. A cell can use these enzymes like on-off switches for the activities of various proteins. Which of the following is probably involved? a. a change in the optimal temperature at which a reaction will occur b. changes in a protein's charge leading to cleavage c. changes in a protein's charge leading to conformational changes d. a change in the optimal pH at which a reaction will occur

changes in a proteins charge leading to conformational changes

What does an enzyme do?

lower the energy activation barrier necessary for the reaction to occur

Firefly luciferase catalyzes the reaction: 1) luciferase + ATP -> adenyl-luciferin + pyrophosphate The next reaction occurs spontaneously: 2) adenyl-luciferin + O2 -> oxyluciferin +H2O + CO2 + AMP + light What is the role of luciferase? a. Luciferase lowers the transition energy of the reaction. b. Luciferase alters the equilibrium point of the reaction. c. Luciferase makes the ∆G of the reaction more negative. d. Luciferase makes the reaction irreversible.

luciferase lowers the transition energy of the reaction

Binding of an allosteric regulator to the enzyme it regulates a. is irreversible. b. is at the enzyme's active site. c. may occur via covalent bonds. d. may occur via ionic bonds

may occur via ionic bonds

A noncompetitive inhibitor for a particular enzyme a. may be "out competed" for binding at the enzyme's binding site by adding a higher concentration of substrate molecules. b. will have a 3-dimensional structure that is similar to that of the enzyme's substrate. c. will bind to the enzyme's active site, preventing binding of substrate molecules. d. None of these answers are correct

none of these answers are correct

A solution of protein at room temperature does not readily decompose to form a solution of amino acids because a. Proteins cannot be hydrolyzed in the presence of so much water. b. Protein hydrolysis is nonspontaneous. c. The hydrolysis of proteins to amino acids is endergonic. d. The activation energy barrier cannot be surmounted.

the activation energy barrier cannot be surmounted

A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because a. Starch hydrolysis is nonspontaneous. b. Starch cannot be hydrolyzed in the presence of so much water. c. The activation energy barrier cannot be surmounted. d. The hydrolysis of starch to sugar is endergonic.

the activation energy barrier cannot be surmounted

Hair is extremely flammable, so why doesn't your hair spontaneously burst into flame? a. Since your hair is generally a mess, burning it would result in a decrease in the total entropy of the universe, which would be a violation of the second law of thermodynamics. b. Burning hair is an endergonic reaction that requires energy from fire to drive it. c. Burning hair is an exergonic reaction that requires energy from fire to drive it. d. The molecules in your hair lack sufficient energy at room temperature to overcome the activation energy barrier for this reaction.

the molecules in your hair lack sufficient energy at room temperature to overcome the activation energy barrier for this reaction

In a particular reversible reaction, "A" and "B" may be converted to "C" and "D", or "C" and "D" may be converted to "A" and "B". The direction of this reversible reaction will be determined by a. whether the enzyme that catalyzes the reaction catalyzes the forward or reverse reactions b. the relative concentrations of "A" and "B" versus "C" and "D" c. Both "a" and "b" are correct. d. None of these answers are correct.

the relative concentrations of A and B versus C and D

When does feedback inhibition occur?

when an end product of a metabolic pathway binds to/inhibits one of the enzymes that catalyzes an early step in that pathway

For the reaction depicted in the figure below, the activation energy barrier for converting C and D to A and B via the enzyme catalyzed reaction is represented by a. arrow C b. arrow A c. arrow E d. arrow B

arrow A

Which of the following statements about ATP and ADP is TRUE? a. ATP acts as an allosteric activator of many enzymes in catabolic pathways while ADP acts as an allosteric inhibitor of many enzymes in catabolic pathways. b. ATP acts as an allosteric inhibitor of many enzymes in catabolic pathways while ADP acts as an allosteric activator of many enzymes in catabolic pathways. c. ATP and ADP act as allosteric inhibitors of many enzymes in anabolic pathways. d. ATP acts as an allosteric inhibitor of many enzymes in anabolic pathways while ADP acts as an allosteric activator of many enzymes in anabolic pathways.

ATP acts as an allosteric inhibitor of many enzymes in catabolic pathways while ADP acts as an allosteric activator of many enzymes in catabolic pathways

Which of the following metabolic processes can occur without a net influx of energy from some other process? a. ADP + Pi → ATP + H2O b. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O c. amino acids → protein d. 6 CO2 + 6 H2O → C6H12O6 + 6 O2

C6H12O6+6O2→6CO2+6H2O

Which of the following is likely to lead to an increase in the concentration of ATP in a cell? a. an increased amino acid concentration b. an increased flux of cofactor molecules c. a decrease in a cell's anabolic activity d. a decrease in a cell's catabolic activity

a decrease in a cells anabolic activity

What is the result of an enzyme?

a greater percentage of the substrate molecules will have sufficient energy to surmount the energy activation barrier (to achieve their highest-energy transition state), allowing the reaction to proceed more quickly.

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's a. free-energy content b. activation energy barrier c. endothermic level d. entropy

activation energy barrier

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 substrate. b. add a noncompetitive inhibitor. c. add more of the enzyme. d. heat the solution to 90°C.

add more of the enzyme

An allosteric regulator a. may decrease the activity level of the enzymes it regulates b. usually acts on multi-subunit enzymes c. All of these answers are correct. d. may increase the activity level of the enzymes it regulates

all of these answers are correct

Different enzymes may lower activation energy barriers by a. providing an environment that is conducive to the reaction. b. stretching substrate molecules towards their transition-state form. c. All of these answers are correct. d. binding different substrate molecules in a way that brings the substrate molecules close together in the correct orientation for a reaction to occur.

all of these answers are correct

Enzyme cofactors a. are needed for some enzymes to be active. b. are not protein molecules. c. All of these answers are correct. d. include vitamins.

all of these answers are correct

The enzyme phosphofructokinase catalyzes the conversion of fructose-6-phosphate and adenosine triphosphate (ATP) to fructose 1,6-bisphosphate and adenosine diphosphate (ADP). Adenosine monophosphate (AMP) activates the enzyme phosphofructokinase (PFK) by binding at a site distinct from the substrate-binding site. This is an example of a. allosteric activation b. activation by an enzyme cofactor c. cooperative activation d. the coupling of exergonic and endergonic reactions

allosteric activation

Which of the following is likely to lead to an increase in the concentration of ATP in a cell? a. an increased flux of cofactor molecules b. an increased amino acid concentration c. an increase in a cell's anabolic activity d. an increase in a cell's catabolic activity

an increase in a cell's catabolic activity

Sucrose is a disaccharide composed of the monosaccharides glucose and fructose. The hydrolysis of sucrose results in a. none of these answers is correct b. breaking of the bond between glucose and fructose and forming new bonds using the atoms from water. c. production of water from the sugar as bonds are broken between the sugar monomers d. bringing glucose and fructose together to form sucrose

breaking of the bond between glucose and fructose and forming new bonds using the atoms from water

How does a noncompetitive inhibitor decrease the rate of an enzyme reaction? a. by changing the free energy change of the reaction b. by acting as a coenzyme for the reaction c. by binding at the active site of the enzyme d. by changing the shape of the enzyme

by changing the shape of the enzyme

Which of the following is NOT a method that cells use to regulate enzyme activities? a. allosteric regulation b. noncompetitive inhibition c. cessation of all enzyme formation d. compartmentalization of enzymes in specific organelles

cessation of all enzyme formation

Vioxx and other prescription nonsteroidal anti-inflammatory drugs (NSAIDs) are potent inhibitors of the cyclooxygenase-2 (COX-2) enzyme. High substrate concentrations reduce the efficacy of inhibition by these drugs. These drugs are a. allosteric regulators b. feedback inhibitors c. competitive inhibitors d. noncompetitive inhibitors

competitive inhibitors

Which of the following statements about enzymes is TRUE? a. Enzymes alter the activation energy barrier for a reaction. b. Enzymes alter ∆G for a reaction. c. Enzymes alter ∆S for a reaction. d. Enzymes alter ∆H for a reaction.

enzymes alter the activation energy barrier for a reason

Which of the following terms best describes the reaction described in the figure below? a. allosteric b. endergonic c. anabolic d. exergonic

exergonic

Which of the following statements is TRUE? a. Inhibition of anabolic enzymes by ATP is an example of feedback inhibition. b. Inhibition of catabolic enzymes by ADP is an example of feedback inhibition. c. Inhibition of catabolic enzymes by ATP is an example of feedback inhibition. d. All of these answers are correct.

inhibition of catabolic enzymes by ATP is an example of feedback inhibition

The active site of an enzyme is the region that a. binds the products of the catalytic reaction b. is involved in the catalytic reaction of the enzyme c. is inhibited by the presence of a coenzyme or cofactor d. binds allosteric regulators of the enzyme

is involved in the catalytic reaction of the enzyme

How quickly do spontaneous reactions occur? a. Extremely quickly b. Very quickly c. It depends on the reaction. Some spontaneous reactions almost never occur. d. Somewhat quickly

it depends on the reaction. some spontaneous reactions almost never occur

Which of the following statements about substrate molecules in their transition state is FALSE? a. Energy is needed to move molecules from their normal to their transition states. b. Molecules in their transition states have increased stability. c. Molecules in their transition states have higher energies than when they are not in their transition states. d. Molecules in their transition states are contorted into unusual shapes

molecules in their transition states have increased stability

The oxidation of glucose to CO2 and H2O is highly exergonic: ∆G = -636 kcal/mol. Why doesn't glucose spontaneously combust? a. The glucose molecules lack the activation energy at room temperature. b. CO2 has higher energy than glucose. c. There is too much CO2 in the air. d. The water molecules quench the reaction.

the glucose molecules lack the activation energy at room temperature

Some bacteria are metabolically active in hot springs because a. they are able to maintain a lower internal temperature. b. their enzymes have high optimal temperatures. c. high temperatures make catalysis unnecessary. d. their enzymes are completely insensitive to temperature.

their enzymes have high optimal temperatures

Which of the following are TRUE for anabolic pathways? a. They consume energy to build up polymers from monomers b. They release energy as they degrade polymers to monomers c. They are usually highly spontaneous chemical reactions d. They do not depend on enzymes

they consume energy to build up polymers from monomers

Which of the following is an example of cooperativity? a. binding of an ATP molecule along with one of the substrate molecules in an active site b. the function of a polypeptide at one site affected by binding of a molecule at another of its active sites c. the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway. d. a substrate molecule binding at one unit of a tetramer allowing faster substrate binding at each of the other three subunits.

a substrate molecule binding at one unit of a tetramer allowing faster substrate binding at each of the other three subunits

Which of the following statements describes enzyme cooperativity? a. A substrate molecule binds to an active site and inhibits cooperation between enzymes in a metabolic pathway. b. A multi-enzyme complex contains all the enzymes of a metabolic pathway. c. The reaction of several substrate molecules can be catalyzed simultaneously by the same enzyme. d. A substrate molecule bound to the active site of one subunit alters the conformation of that subunit and of the other subunits in a multi-subunit enzyme in such a way that the other subunits are able to bind substrate molecules more easily.

a substrate molecule bound to the active site of one subunit alters the conformation of that subunit and of the other subunits in a multi-subunit enzyme in such a way that the other subunits are able to bind substrate molecules more easily

How does a noncompetitive inhibitor decrease the rate of an enzyme reaction? a. by changing the shape of the enzyme b. by binding at the active site of the enzyme c. by acting as a coenzyme for the reaction d. by changing the free energy change of the reaction

by changing the shape of the enzyme

A competitive inhibitor for a particular enzyme a. will compete with the enzyme's substrate for binding to the enzyme's active site b. will have a 3-dimensional structure that is similar to that of the enzyme's substrate c. will be more effective the higher its concentration d. All of these answers are correct.

all of these answers are correct

A competitive inhibitor for a particular enzyme a. will have a 3-dimensional structure that is similar to that of the enzyme's substrate b. will be more effective the higher its concentration c. All of these answers are correct. d. will compete with the enzyme's substrate for binding to the enzyme's active site

all of these answers are correct

Different enzymes may lower energy activation barriers by a. forming a covalent bond with a substrate molecule b. providing an acidic environment for the reaction c. All of these answers are correct. d. providing a basic environment for the reaction

all of these answers are correct

If ATP levels decrease and ADP levels increase a. The rates of many catabolic reactions will increase due to increased allosteric activation by ADP. b. The rates of many anabolic reactions will decrease due to decreased allosteric activation by ATP. c. The rates of many catabolic reactions will increase due to decreased allosteric inhibition by ATP. d. All of these answers are correct.

all of these answers are correct

If ATP levels increase and ADP levels decrease a. All of these answers are correct. b. The rates of many anabolic reactions will increase due to increased allosteric activation by ATP. c. The rates of many catabolic reactions will decrease due to increased allosteric inhibition by ATP. d. The rates of many catabolic reactions will decrease due to decreased allosteric activation by ADP.

all of these answers are correct

If ATP levels increase and ADP levels decrease a. The rates of many anabolic reactions will increase due to decreased allosteric inhibition by ADP. b. The rates of many catabolic reactions will decrease due to increased allosteric inhibition by ATP. c. The rates of many anabolic reactions will increase due to increased allosteric activation by ATP. d. All of these answers are correct.

all of these answers are correct

Which of the following statements comparing allosteric regulators and non-competitive inhibitors is FALSE? a. Non-competitive inhibitors always inhibit (decrease) the activity levels of the enzymes they regulate. b. Both allosteric regulators and non-competitive inhibitors bind at sites that are distinct from the active site(s) they regulate. c. Inhibition by allosteric inhibitors is reversible. d. Allosteric regulators always inhibit (decrease) the activity levels of the enzymes they regulate

allosteric regulators always inhibit the activity levels of the enzymes they regulate

Which of the following statements comparing allosteric regulators and non-competitive inhibitors is TRUE? a. Allosteric regulators may increase or decrease an enzyme's activity level. b. Only non-competitive inhibitors bind at a site that is distinct from the active site(s) they are regulating. c. Inhibition by allosteric regulators is irreversible. d. Only allosteric regulators bind at a site that is distinct from the active site(s) they are regulating

allosteric regulators may increase or decrease an enzyme's activity level

In contrast to non-competitive inhibitors, competitive inhibitors of enzyme activity a. act allosterically. b. cause enzymes to denature. c. can NOT have their effects reversed by addition of more substrate. d. always utilize an enzyme's active site.

always utilize an enzymes active site

Why do scientists sometimes heat a solution to get a reaction to occur at a higher rate? a. Applying heat raises the average energy levels of the reactant molecules, so a greater percentage of the reactant molecules will have sufficient energy to overcome the activation energy barrier. b. Applying heat causes more disorder in both the reactant and product molecules. c. Applying heat causes more disorder in the product molecules, raising their entropy level. d. Applying heat causes more disorder in the reactant molecules, raising their entropy level.

applying heat raises the average energy levels of the reactant molecules, so a greater percentage of the reactant molecules will have sufficient energy to overcome the activation energy barrier.

For the reaction depicted in the figure below, the activation energy barrier for converting C and D to A and B via the non-catalyzed reaction is represented by a. arrow A b. arrow C c. arrow E d. arrow B

arrow E, activation energy barrier is the energy needed for molecules to achieve their highest energy transition state

Wood is extremely flammable, so why don't trees spontaneously burst into flame? a. Burning wood is an exergonic reaction that requires energy from fire to drive it. b. The chemical bonds in wood have more potential energy than the chemical bonds in ash. c. At room temperature, the molecules in wood do not have sufficient energy to overcome the activation energy barrier necessary for this reaction to occur. d. Burning wood is an endergonic reaction that requires energy from fire to drive it.

at room temperature, the molecules in wood do not have sufficient energy to overcome the activation energy barrier necessary for this reaction to occur

How does a noncompetitive inhibitor decrease the rate of an enzyme reaction? a. by changing the free energy of the reaction b. by increasing the activation energy barrier of the reaction c. by changing the free energy of the reactants d. by changing the free energy of the products

by increasing the activation energy barrier of the reaction

When you have a severe fever, what may be a grave consequence if this is not controlled? a. binding of enzymes to inappropriate substrates b. changes in the folding of enzymes c. destruction of your enzyme's primary structure d. removal of amine groups from your proteins

changes in the folding of enzymes

Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? a. insufficient cofactors b. competitive inhibition c. denaturization of the enzyme d. allosteric inhibition

competitive inhibition

Which of the following statements regarding enzymes is FALSE? a. Enzyme function is dependent on the three-dimensional structure or conformation of the enzyme. b. Enzymes alter the free energy change (ΔG) of the reactions which they catalyze. c. Enzyme function is dependent on the pH and temperature of the reaction environment. d. Enzyme activity can be inhibited if the enzyme is bound by a noncompetitive inhibitor.

enzymes alter the free energy change (ΔG) of the reactions which they catalyze

Which of the following statements about enzymes is FALSE? a. Enzymes are not used up by the reactions they catalyze b. Proteins may act as enzymes c. RNA molecules may act as enzymes d. Enzymes increase the free energy of the reactants

enzymes increase the free energy of the reactants

Which of the following statements regarding enzymes is TRUE? a. Enzymes change the direction of chemical reactions. b. Enzymes are permanently altered by the reactions they catalyze. c. Enzymes increase the rate of a reaction. d. Enzymes decrease the free energy of a reaction.

enzymes increase the rate of a reaction

Which of the following is the best explanation for how enzymes speed up the rates of reactions? a. Enzymes increase the energy of the reactant molecules. b. Enzymes increase the enthalpy of the reactant molecules. c. Enzymes lower the energy required for reactant molecules to reach their transition state. Enzymes do not alter the free or total energies of the reactant or product molecules. d. Enzymes lower the free energy change of the reaction.

enzymes lower the energy required for reactant molecules to reach their transition state enzymes do not alter the free or total energies of the reactant or product molecules

Which of the following is the best explanation for how enzymes speed up the rates of reactions? a. Enzymes lower the free energy change of the reaction. b. Enzymes increase the energy of the reactant molecules. c. Enzymes lower the energy required for reactant molecules to reach their transition state. Enzymes do not alter the free or total energies of the reactant or product molecules. d. Enzymes increase the enthalpy of the reactant molecules.

enzymes lower the energy required for reactant molecules to reach their transition state. Enzymes do not alter the free or total energies of the reactant or product molecules.

A series of enzymes catalyzes the series of reactions shown below. 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. Substance A functions in X -> Y -> Z -> A a. catabolic inhibition b. feedback inhibition c. noncooperative inhibition d. metabolic inhibition

feedback inhhibition

The mechanism by which the end product of a metabolic pathway inhibits an enzyme that catalyzes an earlier step in the pathway is known as a. metabolic inhibition b. allosteric inhibition c. feedback inhibition d. noncooperative inhibition

feedback inhibition

Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. What role does malonic acid play in this reaction? a. It is a competitive inhibitor. b. It replaces the usual enzyme. c. It blocks the binding of fumarate. d. It is a noncompetitive inhibitor.

it is a competitive inhibitor

Feedback inhibition is used by cells to a. slow down the rate at which organisms consume food. b. keep from producing unnecessarily high levels of different products. c. decrease the free energy change of undesirable reactions. d. slow down the rate at which organisms excrete waste products.

keep from producing unnecessarily high levels of different products

If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur? a. Additional product will be formed. b. Nothing; the reaction will stay at equilibrium. c. The free energy of the system will change. d. The reaction will change from endergonic to exergonic.

nothing; the reaction will stay at equilibrium

You notice that many of the anabolic reactions in a cell have speeded up. Upon further characterization of the cell, you are NOT surprised to find that a. both the ATP and ADP levels in the cell are low. b. the ATP levels in the cell are low and the ADP levels are high. c. the ATP levels in the cell are high and the ADP levels are low. d. both the ATP and ADP levels in the cell are high.

the ATP levels in the cell are high and the ADP levels are low

You notice that many of the catabolic reactions in a cell have speeded up. Upon further characterization of the cell, you are NOT surprised to find that a. the ATP levels in the cell are high and the ADP levels are low. b. the ATP levels in the cell are low and the ADP levels are high. c. both the ATP and ADP levels in the cell are low. d. both the ATP and ADP levels in the cell are high

the ATP levels in the cell are low and the ADP levels are high

Wood does not burst into flame on its own. Yet, once you start a campfire, the wood continues to burn. What is going on? a. The burnt part of the wood releases ash and smoke, raising the entropy of the products of the reaction. b. The combustion of wood is an endergonic process. Once you start the wood burning, heat is released by the burning wood. That heat increases the energy of other molecules in the wood, so that they now have sufficient energy to overcome the activation energy barrier and begin to burn as well. c. The burnt part of the wood releases ash and smoke, raising the entropy of the system. d. The combustion of wood is an exergonic process. Once you start the wood burning, heat is released by the burning wood. That heat increases the energy of other molecules in the wood, so that they now have sufficient energy to overcome the activation energy barrier and begin to burn as well.

the combustion of wood is an exergonic process. Once you start the wood burning, heat is released by the burning wood. That heat increases the energy of other molecules in the wood, so that they now have sufficient energy to overcome the activation energy barrier and begin to burn as well.