Deck 6: An Introduction to Metabolism

Question 1

Which of the following reactions release energy?

A)endergonic reactions
B)dehydration reactions
C)hydrolysis reactions
D)formation of water from hydrogen and hydroxyl ions

Answer 1

C

Question 2

Which of the following is the most comprehensive definition of metabolism in living organisms?

A)Metabolism depends on a constant supply of energy from food.
B)Metabolism manages the increase of entropy in an organism.
C)Metabolism refers to the sum of all biochemical pathways involved in synthesis of macromolecules.
D)Metabolism consists of all the energy transformation reactions in an organism.

Answer 2

D

Question 3

Which of the following statements is a logical consequence of the second law of thermodynamics?

A)If the entropy of a system increases,there must be a corresponding decrease in the entropy of the universe.
B)If there is an increase in the energy of a system,there must be a corresponding decrease in the energy of the rest of the universe.
C)Every energy transfer requires activation energy from the environment.
D)Every chemical reaction must increase the total entropy of the universe.

Answer 3

D

Question 4

ATP hydrolysis in a test tube releases only about half as much energy as ATP hydrolysis in the cell.Which of the following statements is the best explanation for this observation?

A)Cells maintain higher internal pressure,which speeds up the reaction rate.
B)Reactant and product concentrations in the cell are different from the standard conditions used in a test tube.
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.

Question 5

Which of the following statements best describes the critical role that ATP plays in cellular metabolism?

A)The covalent bond on the terminal phosphate of ATP is particularly strong,so it releases extra energy when hydrolyzed.
B)It is one of the four building nucleotides required for DNA synthesis.
C)ATP hydrolysis provides the energy used to power exergonic reactions in the cell.
D)ATP serves as an energy shuttle in the cell,coupling exergonic and endergonic reactions.

Question 6

Which of the following descriptions would be an example of potential energy?

A)the movement of a bicycle coasting down a hill
B)flood water rushing through a breach in a dam
C)a spark emitted by explosion of a firework
D)the chemical bonds in a molecule of sucrose

Question 7

The cellular process of synthesizing large molecules from smaller ones is defined as

A)catalysis.
B)metabolism.
C)anabolism.
D)dehydration.
E)catabolism.

Question 8

Which of the following reactions tend to require an input of energy?

A)exergonic
B)dehydration
C)hydrolysis
D)catabolic

Question 9

Anabolic pathways share which of the following characteristics?

A)They are not dependent on enzymes.
B)They are usually spontaneous chemical reactions that do not require an input of energy.
C)They consume energy to synthesize polymers from monomers.
D)They release energy as they degrade polymers to monomers.

Question 10

Energy transformations in organisms are always associated with

A)a decrease in the free energy of the organism.
B)an increase in the free energy of the universe.
C)an increase in the entropy of the organism.
D)an increase in the entropy of the universe.

Question 11

A chemical reaction that has a positive ΔG is best described as

A)endergonic.
B)at equilibrium.
C)spontaneous.
D)exergonic.

Question 12

The free-energy change for the hydrolysis of ATP to ADP + ℗_i,under standard conditions (1 M concentration of both reactants and products)is -7.3 kcal/mol.However,in the cytoplasm of the cell,the free-energy change is about -13 kcal/mol.Based on this observation,what would you predict the free-energy change for the reverse reaction (formation of ATP from ADP and ℗_i)would be under cellular conditions?

A)about +7.3 kcal/mol
B)less than +7.3 kcal/mol
C)about +13 kcal/mol
D)about +26 kcal/mol

Question 13

Based on the first law of thermodynamics,which of the following statements about a living organism is true?

A)The energy content of an organism is constant.
B)The organism ultimately must obtain all of the necessary energy for life from its environment.
C)The entropy of an organism decreases with time as the organism grows in complexity.
D)An organism grows by converting energy into organic matter.

Question 14

The cellular process of breaking down large molecules into smaller ones is defined as

A)catalysis.
B)metabolism.
C)anabolism.
D)dehydration.
E)catabolism.

Question 15

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.

Question 16

Which of the following statements about a system at chemical equilibrium is true?

A)The system consumes energy at a steady rate.
B)The system releases energy at a steady rate.
C)Over time,the system will spontaneously move away from equilibrium.
D)The system can do no work.

Question 17

Which of the following types of reactions would decrease the entropy within a cell?

A)anabolic reactions
B)hydrolysis
C)catabolic reactions
D)digestion

Question 18

Which of the following statements 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.

Question 19

Which of the following statements is representative of the second law of thermodynamics?

A)Conversion of energy from one form to another is always accompanied by some gain of free energy.
B)Heat represents a form of energy that can be used by most organisms to do work.
C)Without an input of energy,organisms would tend toward decreasing entropy.
D)Cells require a constant input of energy to maintain their high level of organization.

Question 20

Living organisms increase in complexity as they grow,resulting in a decrease in the entropy of an organism.How does this relate to the second law of thermodynamics?

A)Living organisms do not obey the second law of thermodynamics,which states that entropy must increase with time.
B)The complexity is actually associated with greater disorder than the level of disorder associated with the organism at early stages of development.
C)As a consequence of growing,organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.
D)Living organisms are able to transform energy into entropy.

Question 21

Hydrolysis of ATP releases energy,which ultimately results in the production of ADP and inorganic phosphate.What generally happens to the inorganic phosphate produced in the cytosol?

A)It is secreted as waste.
B)It is combined with ADP to regenerate ATP.
C)It is stored in the rough ER.
D)It is further broken down to release additional energy.

Question 22

Which of the following processes would be an example of a catabolic pathway?

A)combining small molecules into larger,more energy-rich molecules
B)providing energy that can be used to drive cellular work
C)any endergonic reaction in a cell
D)production of complex molecules such as protein from simpler compounds

Question 23

When chemical,transport,or mechanical work is performed by an organism,what happens to the heat that is 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.

Question 24

Which of the following statements best describes the induced fit model of enzyme activity?

A)The binding of substrate depends on the conformation of the active site.
B)The binding of an activator alters 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 so that it binds substrate less tightly.

Question 25

In addition to its critical role in cellular metabolism,ATP may also be described as 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

Question 26

A solution of starch at room temperature does not readily decompose to form a solution of glucose because

A)the starch solution has less free energy than a solution of glucose.
B)the hydrolysis of starch to glucose is endergonic.
C)the activation energy barrier for this reaction cannot easily be overcome at room temperature.
D)starch hydrolysis is nonspontaneous.

Question 27

A mutation that results in a single amino acid substitution in the active site of an enzyme may have which of the following consequences?

A)It may alter the ability of a noncompetitive inhibitor to bind to the enzyme.
B)It may alter the ability of an allosteric regulator to effect enzyme activity.
C)It may change the substrate specificity of the enzyme.
D)It may change the ∆G for the original reaction catalyzed by the enzyme.

Question 28

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

Question 29

What is the difference (if any)between the structure of ATP and the structure of the A nucleoside triphosphate used to make DNA?

A)The sugar molecule is different.
B)The nitrogen-containing base is different.
C)The number of phosphates is three in ATP instead of one in DNA.
D)There is no difference;they are the same molecule.

Question 30

Hydrolysis of ATP releases energy,which ultimately results in the production of ADP and inorganic phosphate.What is commonly the immediate fate of the phosphate released by ATP hydrolysis in the cell?

A)It is secreted as waste.
B)It diffuses through an ion channel into the Golgi apparatus,where it modifies secreted proteins.
C)It is attached to ADP to regenerate ATP.
D)It is attached to a substrate to form a phosphorylated intermediate.

Question 31

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)The activation energy required for the reaction to proceed is greater than when the same reaction occurs in the absence of an enzyme.
D)Energy from ATP is required to activate the enzyme before it can catalyze the reaction.

Question 32

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.

Question 33

In most exergonic reactions,before products can be formed,the reactants 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.

Question 34

A mutation that alters a single amino acid in a region of the enzyme outside of the active site may result in which of the following consequences?

A)It may alter the ability of a competitive inhibitor to bind to the enzyme.
B)It will generally inactivate the enzyme.
C)It will generally change the substrate specificity of the enzyme.
D)It may alter an allosteric site on the enzyme.

Question 35

Which of the following is an example of an anabolic pathway?

A)a set of reactions that combine monomers into larger,more energy-rich polymers
B)a set of coupled reactions that are exergonic
C)a set of reactions that break covalent bonds between molecules to release free energy
D)a set of reactions that release energy that can be used to drive cellular work

Question 36

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 blocked by the presence of a coenzyme or a cofactor.

Question 37

Which of the descriptions below is an example of 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

Question 38

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

Question 39

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.

Question 40

What is the difference (if any)between the structure of ATP and the structure of the A nucleoside triphosphate used to make RNA?

A)The sugar molecule is different.
B)The nitrogen-containing base is different.
C)The number of phosphates is three in ATP instead of one in RNA.
D)There is no difference;they are the same molecule.

Question 41

Which of the following statements is true of enzymes?

A)Required nonprotein cofactors generally alter the substrate specificity of enzymes.
B)Enzyme function is generally increased if the three-dimensional conformation of an enzyme is altered.
C)Enzyme function is generally independent of physical and chemical environmental factors such as pH and temperature.
D)Enzymes generally increase the rate of chemical reactions by lowering activation energy barriers.

Question 42

The activity of many cellular enzymes is regulated by activators and inhibitors.Enzyme activity is also regulated in eukaryotic cells by which of the following mechanisms?

A)compartmentalization and restricting enzymes to specific organelles or membranes
B)limiting the availability of substrates
C)changing the primary structure of enzymes
D)secreting enzymes out of the cell

Question 43

Figure 6.1
Which of the following is the most correct interpretation of Figure 6.1?

A)Inorganic phosphate is created from organic phosphate.
B)Energy from catabolism can be used directly for performing cellular work.
C)ADP + ℗_i are a set of molecules that store energy for catabolism.
D)ATP is a molecule that acts as an intermediary to store energy for cellular work.

Question 44

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 with altered substrate specificity had multiple amino acid changes.Where in the enzyme might these amino acid changes be located?

A)only in or near the active site
B)only in the hydrophobic interior of the folded protein
C)only on surface sites distant from the active site
D)in or near the active site,in the hydrophobic interior,and/or at surface sites distant from the active site

Question 45

The mechanism by which the end product of a metabolic pathway inhibits an enzyme that catalyzes an earlier step in the pathway is most precisely described as

A)competitive inhibition.
B)cooperativity inhibition.
C)irreversible inhibition.
D)feedback inhibition.

Question 46

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.

Question 47

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 at this point.Which of the following would be a likely next step in the reaction 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,which allows 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,followed by binding of a new amino acid.
C)Hydrolysis of ATP phosphorylates the amino acid,which results in a conformational change in the active site that 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.

Question 48

A mutation results in an amino acid substitution at a site distant from the active site of an enzyme.How might this amino acid change alter the active site and substrate specificity of the enzyme?

A)by changing the optimum temperature for the enzyme
B)by changing the intracellular location of the enzyme
C)by changing the binding site for an allosteric regulator
D)by changing the conformation of the enzyme

Question 49

In Figure 6.2,why does the reaction rate plateau at higher reactant concentrations?

A)Feedback inhibition by the product occurs at high reactant concentrations.
B)Most enzyme molecules are occupied by substrate at high reactant concentrations.
C)The reaction nears equilibrium at high reactant concentrations.
D)The activation energy for the reaction increases with reactant concentration.

Question 50

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 temperature of the reaction

Question 51

Cells use the ATP cycle shown in Figure 6.1 to perform which of the following processes?

A)recycle ADP and phosphate
B)recycle energy released by ATP hydrolysis
C)recycle the energy used for cellular work
D)move energy from ATP to ADP

Question 52

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.

Question 53

An enzyme-catalyzed reaction is conducted in a test tube with a fixed amount of enzyme.Increasing the enzyme concentration in the test tube may overcome the effect of which of the following conditions?

A)denaturation of the enzyme
B)presence of a fixed amount of an allosteric inhibitor
C)presence of a fixed amount of a competitive inhibitor
D)a saturated enzyme population

Question 54

Zinc,an essential trace element for most organisms,is required in the active site of the enzyme carboxypeptidase in order for the enzyme to function properly.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.

Question 55

For the enzyme-catalyzed reaction shown in Figure 6.2,which of these treatments will cause the greatest increase in the rate of the reaction if the initial reactant concentration is 1.0 micromolar?

A)doubling the activation energy needed
B)cooling the reaction by 10°C
C)doubling the concentration of the reactants to 2.0 micromolar,while reducing the concentration of enzyme by half
D)doubling the enzyme concentration

Question 56

Why might a severe fever result in death if it is not brought under control?

A)It may destroy the primary structure of cellular enzymes.
B)It may alter the tertiary and quaternary structures of cellular enzymes.
C)It may increase the rate of cellular chemical reactions.
D)It may result in consumption of excess ATP.

Question 57

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 an enzyme,which promotes faster binding to each of the other subunits of the enzyme
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

Question 58

Figure 6.3 Activity of various enzymes (a)at various temperatures and (b)at various pH.
Which curves on the graphs in Figure 6.3 may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot spring 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

Question 59

An enzyme-catalyzed reaction is conducted in a test tube with a fixed amount of enzyme.Increasing the substrate concentration in the test tube may overcome the effect of which of the following conditions?

A)denaturation of the enzyme
B)presence of a fixed amount of an allosteric inhibitor
C)presence of a fixed amount of a competitive inhibitor
D)a saturated enzyme population

Question 60

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

Question 61

Which of the following metabolic processes can occur without a net influx of energy from some other process?

A)ADP + _i → ATP + H₂O
B)C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O
C)6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
D)amino acids → protein

Question 62

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.

Question 63

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.Which of the following statements regarding the molecules involved in this reaction 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.

Question 64

Figure 6.3 Activity of various enzymes (a)at various temperatures and (b)at various pH.
Which temperature and pH profile curves on the graphs in Figure 6.3 were most likely generated from analysis of an enzyme from a human stomach,where conditions are strongly acidic?

A)curves 1 and 4
B)curves 1 and 5
C)curves 2 and 4
D)curves 2 and 5
E)curves 3 and 4

Question 65

Figure 6.4
Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction
A + B ↔ C + D.Which of the following changes in free-energy represents the difference between the free-energy content of the reactants and the free-energy content of the products?

A)a
B)b
C)c
D)d
E)e

Question 66

Figure 6.4
Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction A + B ↔ C + D.Which of the following changes in free-energy represents the overall ΔG for the reaction?

A)a
B)b
C)c
D)d
E)e

Question 67

Figure 6.4
Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction
A + B ↔ C + D.Which of the following changes in free-energy would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?

A)a
B)b
C)c
D)d
E)e

Question 68

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.

Question 69

Figure 6.4
Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction
A + B ↔ C + D.Which of the following represents change in free-energy for the reverse reaction,C + D → A + B?

A)a
B)b
C)c
D)d
E)e

Question 70

Figure 6.4
Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction
A + B ↔ C + D.Which of the following changes in free-energy represents the activation energy required for the enzyme-catalyzed reaction?

A)a
B)b
C)c
D)d
E)e

Question 71

Figure 6.4
Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction
A + B ↔ C + D.Which of the following changes in free-energy represents the activation energy required for a noncatalyzed reaction?

A)a
B)b
C)c
D)d
E)e

Question 72

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.The effect of malonic acid on the activity of succinate dehydrogenase suggests which of the following?

A)Malonic acid is a noncompetitive inhibitor.
B)Malonic acid is a competitive inhibitor.
C)Malonic acid blocks the binding of fumarate.
D)Malonic acid is an allosteric regulator.

Question 73

Figure 6.4
Figure 6.4 illustratesvarious aspects of the free-energy change (ΔG)for the reaction A + B ↔ C + D.Which of the following best describes the forward reaction?

A)endergonic,∆G > 0
B)exergonic,∆G < 0
C)endergonic,∆G < 0
D)exergonic,∆G > 0

Question 74

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 of A decreases the activity of the enzyme that converts X to Y.What is substance X?

A)a coenzyme
B)an allosteric inhibitor
C)an intermediate
D)a substrate

Question 75

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.

Question 76

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

Question 77

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.

Question 78

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.

Question 79

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 of A decreases the activity of the enzyme that converts X to Y.The product A functions as which of the following in terms of its effect on the enzyme that converts X to Y?

A)a coenzyme
B)an allosteric inhibitor
C)a substrate
D)a metabolic intermediate
E)a competitive inhibitor