chapter 8 multiple choice
A series of enzymes catalyze the reaction 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) an allosteric inhibitor B) a substrate
B (a substrate)
Anabolic pathways _____. A) are usually highly spontaneous chemical reactions B) consume energy to build up polymers from monomers C) release energy as they degrade polymers to monomers
B (consume energy to build up polymers from monomers)
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
B (exergonic; endergonic)
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity? A) localization of enzymes into specific organelles or membranes B) exporting enzymes out of the cell
B (exporting enzymes out of the cell)
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as _____. A) metabolic inhibition B) feedback inhibition C) allosteric inhibition
B (feedback inhibition)
You have isolated a previously unstudied protein, identified its complete structure in detail, and determined that it catalyzes the breakdown of a large substrate. You notice it has two binding sites. One of these is large, apparently the bonding site for the large substrate; the other is small, possibly a binding site for a regulatory molecule. What do these findings tell you about the mechanism of this protein? A) It is probably a structural protein that is involved in cell-to-cell adhesion. B) It is probably an enzyme that works through allosteric regulation.
B (it is probably an enzyme that works through allosteric regulation)
Why is ATP an important molecule in metabolism? A) Its hydrolysis provides an input of free energy for exergonic reactions. B) It provides energy coupling between exergonic and endergonic reactions. C) Its terminal phosphate group contains a strong covalent bond that, when
B (it provides energy coupling between exergonic and endergonic reactions)
Catabolic pathways _____. A) combine molecules into more energy-rich molecules B) supply energy, primarily in the form of ATP, for the cell's work C) are endergonic
B (supply energy, primarily in the form of ATP, for the cells work)
Most cells cannot harness heat to perform work because _____. A) heat is not a form of energy B) temperature is usually uniform throughout a cell C) heat can never be used to do work
B (temperature is usually uniform throughout a cell)
A series of enzymes catalyze the reaction 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) an allosteric inhibitor B) the substrate
A (an allosteric inhibitor)
Which of the following types of reactions would decrease the entropy within a cell? A) anabolic reactions B) hydrolysis C) digestion
A (anabolic reaction)
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones? A) catabolism (catabolic pathways) B) metabolism C) anabolism (anabolic pathways)
A (catabolism or catabolic pathway)
Which of the following involves a decrease in entropy? A) condensation reactions B) reactions that separate monomers C) depolymerization reactions
A (condensation reaction)
A chemical reaction that has a positive ΔG is best described as _____. A) endergonic B) enthalpic C) spontaneous
A (endergonic)
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.
A (energy cannot be created or destroyed)
Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellular eukaryotic organisms, _____. A) has occurred in accordance with the laws of thermodynamics B) has caused an increase in the entropy of the planet C) has been made possible by expending Earth's energy resources
A (has occurred in accordance with the laws of thermodynamics)
In solution, why do hydrolysis reactions occur more readily than condensation reactions? A) Hydrolysis increases entropy and is exergonic. B) Hydrolysis raises G, or Gibbs free energy. C) Hydrolysis decreases entropy and is exergonic. D) Hydrolysis increases entropy and is endergonic.
A (hydrolysis increases entropy and is exergonic)
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 malonic acid's role with respect to succinate dehydrogenase? Malonic acid _____. A) is a competitive inhibitor B) blocks the binding of fumarate
A (is a competitive inhibitor)
Biological systems use free energy based on empirical data that all organisms require a constant energy input. The first law of thermodynamics states that energy can be neither created nor destroyed. For living organisms, which of the following statements is an important consequence of this first law? A) The energy content of an organism is constant except for when its cells are dividing. B) The organism must ultimately obtain all the necessary energy for life from its environment.
B (the organism must ultimately obtain all the necessary energy for life from its environment)
For living organisms, which of the following is an important consequence of the first law of thermodynamics? 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.
B (the organism ultimately must obtain all of the necessary energy for life from its environment)
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.
B (the reaction proceeds with a net release of free energy)
Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by their plasma membrane localization? A) ATP is more abundant near the plasma membrane. B) They can more readily encounter and phosphorylate other membrane proteins.
B (they can more readily encounter and phosphorylate other membranes proteins)
Which of the following is an example of cooperativity? A) the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway B) one enzyme in a metabolic pathway passing its product to act as a substrate for the next enzyme in the pathway C) a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
C ( a molecule binding at one unit of a tetramer allowing faster binding at each of the other three)
The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are) correct? A) ΔS is the change in enthalpy, a measure of randomness. B) ΔH is the change in entropy, the energy available to do work. C) ΔG is the change in free energy.
C (Delta G is the change in free energy)
Which of the following is true of metabolism in its entirety in all organisms? A) Metabolism depends on a constant supply of energy from food. B) Metabolism uses all of an organism's resources. C) Metabolism consists of all the energy transformation reactions in an organism.
C (Metabolism consists of all the energy transformation reactions in an organism)
Which of the following is most similar in structure to ATP? A) a pentose sugar B) a DNA nucleotide C) an RNA nucleotide
C (RNA nucleotide)
Which of the following is an example of potential rather than kinetic energy? A) water rushing over Niagara Falls B) light flashes emitted by a firefly C) a molecule of glucose
C (a molecule of glucose)
Allosteric enzyme regulation is usually associated with _____. A) feedback inhibition B) activating activity C) an enzyme with more than one subunit D) the need for cofactors
C (an enzyme with more than one subunit)
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) Life obeys the second law of thermodynamics because the decrease in entropy as the organism grows is exactly balanced by an increase in the entropy of the universe. 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.
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.
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) Without an input of energy, organisms would tend toward decreasing entropy. C) Cells require a constant input of energy to maintain their high level of organization.
C (cells require a constant input of energy to maintain their high level of organization)
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 chemical reaction must increase the total entropy of the universe.
C (every chemical reaction must increase the total entropy of the universe)
In a biological reaction, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount of succinate molecules to those of malonic acid reduces the inhibitory effect if malonic acid. Select the correct identification of the molecules described in the reaction. A) Succinate dehydrogenase is the enzyme, and fumarate is the substrate in the reaction. B) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate in the reaction. C) Succinate is the substrate, and fumarate is the product in the reaction.
C (succinate is the substrate and fumarate is the product in the reaction)
Chemical equilibrium is relatively rare in living cells. An example of a reaction at chemical equilibrium in a cell would be _____. A) one in which the free energy at equilibrium is higher than the energy content at any point away from equilibrium B) one in which the entropy change in the reaction is just balanced by an opposite entropy change in the cell's surroundings C) an endergonic reaction in an active metabolic pathway where the energy for that reaction is supplied only by heat from the environment D) a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway at that time in the cell
D (a chemical reaction in which both the reactant and products are not being produced or used in any active metabolic pathway at that time in the cell)
A system at chemical equilibrium _____. A) consumes energy at a steady rate B) releases energy at a steady rate C) has zero kinetic energy D) can do no work
D (can do not work)
HIV is the virus that causes AIDS. In the mid-1990s, researchers discovered an enzyme in HIV called protease. Once the enzyme's structure was known, researchers began looking for drugs that would fit into the active site and block it. If this strategy for stopping HIV infections were successful, it would be an example of what phenomenon? A) vaccination B) denaturation C) allosteric regulation D) competitive inhibition
D (competitive inhibition)
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 as more ATP. C) It is used to generate ADP from nucleotide precursors. D) It is lost to the environment.
D (it is lost to the environment)
When 10,000 molecules of ATP are hydrolyzed to ADP and i in a test tube, about half as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation? A) Cells are open systems, but a test tube is an isolated system. B) Cells are less efficient at heat production than nonliving systems. C) The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes. D) Reactant and product concentrations in the test tube are different from those in the cell.
D (reactant and product concentrations in the test tube are different from those in the cell)
