BIO 111 - Chapter 6 Mastering Biology

Which of the following statements regarding enzymes is true? A. Enzymes increase the rate of a reaction by lowering the activation energy barrier. B. Enzymes change the equilibrium point of the reactions they catalyze. C. Enzymes increase the rate of a reaction by making the reaction more exergonic. D. Enzymes increase the rate of a reaction by reducing the rate of reverse reactions.

A. Enzymes increase the rate of a reaction by lowering the activation energy barrier.

Which of the following statements concerning catabolic pathways is true? A. They provide energy that can be used to drive cellular work. B. They are endergonic. C. They build up complex molecules such as protein from simpler compounds. D. They combine molecules into larger, more energy-rich molecules. Submit

A. They provide energy that can be used to drive cellular work.

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 substrate B. an intermediate C. a coenzyme D. an allosteric inhibitor

A. a substrate

The cellular process of breaking down large molecules into smaller ones is defined as A. catabolism B. metabolism C. catalysis D. dehydration E. anabolism

A. catabolism

Which of the following statements is a logical consequence of the second law of thermodynamics? A. Every energy transfer requires activation energy from the environment. B. Every chemical reaction must increase the total entropy of the universe. C. If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe. D. 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. E. Energy can be transferred or transformed, but it cannot be created or destroyed.

B. Every chemical reaction must increase the total entropy of the universe.

Which of the following is an example of potential rather than kinetic energy? A. water rushing over Niagara Falls B. a molecule of glucose C. light flashes emitted by a firefly D. the muscle contractions of a person mowing grass Submit

B. a molecule of glucose

A catabolic pathway may be which of the following? A. a set of coupled reactions that are endergonic B. a set of reactions that release energy that can be used to drive cellular work C. a set of reactions that form covalent bonds between molecules to store free energy D. a set of reactions that combine monomers into larger, more energy-rich polymers

B. a set of reactions that release energy that can be used to drive cellular work

In most exergonic reactions, the reactants capable of interacting to form products typically must first overcome a thermodynamic barrier known as the A. chemical equilibrium of the reaction. B. activation energy of the reaction. C. entropy of the reaction. D. energy conservation of the reaction.

B. activation energy of the reaction.

Which of the following types of reactions would decrease the entropy within a cell? A. digestion B. anabolic reactions C. catabolic reactions D. diffusion E. hydrolysis

B. anabolic reactions

The cellular process of synthesizing large molecules from smaller ones is defined as A. metabolism B. anabolism C. catalysis D. dehydration E. catabolism

B. anabolism

A chemical reaction that has a positive ΔG is best described as A. entropic B. endergonic C. exergonic D. spontaneous

B. endergonic

Which of the following tend(s) to release energy? A. dehydration reactions B. hydrolysis reactions C. formation of water from hydrogen and hydroxyl ions D. endergonic reactions Submit

B. hydrolysis reactions

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 change the substrate specificity of the enzyme. C. may alter the G for the reaction catalyzed by the enzyme. D. may alter the ability of an allosteric regulator to alter enzyme activity. Submit

B. may change the substrate specificity of the enzyme.

The active site of an enzyme is the region that A. binds noncompetitive inhibitors of the enzyme. B. binds allosteric regulators of the enzyme. C. binds substrates for the enzyme. D. is inhibited by the presence of a coenzyme or a cofactor.

C. binds substrates for the enzyme.

Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? A. denaturation of the enzyme B. saturation of the enzyme activity C. competitive inhibition D. allosteric inhibition

C. competitive inhibition

The mechanism by which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as A. irreversible inhibition. B. noncooperative inhibition. C. metabolic inhibition. D. feedback inhibition.

D. feedback inhibition.

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. ATP hydrolysis in a cell produces different products than ATP hydrolysis in a test tube. B. ATP hydrolysis in cells is catalyzed by enzymes, which releases more energy than the uncatalyzed reaction in a test tube. C. Cells maintain higher internal pressure, which speeds up the reaction rate. D. ATP hydrolysis in a test tube occurs under standard conditions; in the cell, reactant and product concentrations differ from standard conditions.

D. ATP hydrolysis in a test tube occurs under standard conditions; in the cell, reactant and product concentrations differ from standard conditions.

The reaction proceeds with a net release of free energy. A. It is used to store energy in the form of ATP. B. It is used to power yet more cellular work. C. It is used to synthesize ADP. D. It is released to the environment.

D. It is released to the environment.

Which of the following is true for all exergonic reactions? A. The products have more total energy than the reactants. B. A net input of energy from the surroundings is required for the reaction to proceed. 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. The reaction proceeds with a net release of free energy. Submit

D. The reaction proceeds with a net release of free energy.

A system at chemical equilibrium A. releases energy at a steady rate. B. consumes energy at a steady rate. C. consumes or releases energy at a steady rate, depending on whether it is exergonic or endergonic. D. can do no work. Submit

D. can do no work. Submit

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. at an allosteric site B. at a cofactor binding site C. in regions of the enzyme that determine packaging into the virus capsid D. in or near the active site

D. in or near the active site

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. With respect to the enzyme that converts X to Y, substance A functions as A. a competitive inhibitor. B. the substrate. C. a coenzyme. D. an intermediate. E. an allosteric inhibitor.

E. an allosteric inhibitor.