Chapter 6

Which of the following types of reactions would decrease the entropy within a cell? a. catabolic reactions b. hydrolysis c. diffusion d. digestion e. anabolic reactions

anabolic reactions

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

anabolism

An enzyme is considered _____ because of its ability to recognize the shape of a particular molecule.

specific

In a catalyzed reaction, a reactant is often called a ___.

substrate

A substrate binds to an enzyme at the ___, where the reaction occurs.

active site

Which of the following is true of enzymes? A. Enzymes increase the rate of chemical reaction by lowering activation energy barriers. 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 providing activation energy to the substrate. E. Nonprotein cofactors alter the substrate specificity of enzymes.

A. Enzymes increase the rate of chemical reaction by lowering activation energy barriers.

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. What is the role of malonic acid with respect to succinate dehydrogenase? A. It is a competitive inhibitor. B. It is a noncompetitive inhibitor. C. It is an allosteric regulator. D. It blocks the binding of fumarate.

A. It is a competitive inhibitor.

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

A. feedback inhibition.

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. The rate of the reaction is greater than when the same reaction occurs in the absence of an enzyme.

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

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

A noncompetitive inhibitor decreases the rate of an enzymatic reaction by A. changing the G for the reaction. B. changing the shape of the enzyme active site. C. binding to the active site of the enzyme. D. decreasing the activation energy required for the reaction.

B. changing the shape of the enzyme active site.

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. coenzyme derived from a vitamin. B. cofactor necessary for enzyme activity. C. noncompetitive inhibitor of the enzyme. D. competitive inhibitor of the enzyme. E. allosteric activator of the enzyme.

B. cofactor necessary for enzyme activity.

Which of the following is an example of cooperativity? A. binding of an ATP molecule along with another substrate in an active site B. the product of one enzyme in a metabolic pathway serving as the substrate for the next enzyme in the pathway C. binding of a molecule to one subunit of a tetramer, which promotes faster binding to each of the other three subunits D. binding of the end product of a metabolic pathway to the enzyme that catalyzes the first step in the pathway

C. binding of a molecule to one subunit of a tetramer, which promotes faster binding to each of the other three subunits

The active site of an enzyme is the region that A. binds allosteric regulators of the enzyme. B. binds noncompetitive inhibitors 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.

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

C. may change the substrate specificity of the enzyme.

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 reducing the rate of reverse reactions. C. Enzymes change the equilibrium point of the reactions they catalyze. D. Enzymes increase the rate of a reaction by lowering the activation energy barrier.

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

Which of the following is true for all exergonic reactions? A. The reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted to reactants. B. The products have more total energy than the reactants. C. A net input of energy from the surroundings is required for the reaction to proceed. D. The reaction proceeds with a net release of free energy.

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

Some bacteria are metabolically active in hot springs because __________. A. they are able to maintain a lower internal temperature B. their enzymes are completely insensitive to temperature C. high temperatures make catalysis unnecessary D. their enzymes have high optimal temperatures

D. their enzymes have high optimal temperatures

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

catabolism

An enzyme is considered a ___ because it speeds up chemical reactions without being used up.

catalyst

a _____, such as a vitamin, binds to an enzyme and plays a role in catalysis

cofactor

When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) _____.

complex

An enzyme is ___ when it loses its native conformation and its biological activity.

denatured