Chapter 8 Mastering Biology

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _______ is to _______. 1) free energy; entropy 2) exergonic; spontaneous 3) work; energy 4) exergonic; endergonic 5) entropy; enthalpy

4

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 of malonic acid. Select the correct identification of the molecules described in the reaction. 1) Succinate is the substrate, and fumarate is the product in the reaction. 2) Fumarate is the product, and malonic acid is a noncompetitive inhibitor in the reaction. 3) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate in the reaction. 4) Succinate dehydrogenase is the enzyme, and fumarate is the substrate in the reaction.

1

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's 1) activation energy. 2) free-energy content. 3) equilibrium point. 4) entropy. 5) endothermic level.

1

The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation? 1) The compound is a competitive inhibitor. 2) The compound forms a covalent bond with one of the amino acid residues needed for enzyme activity. 3) The compound reduces disulfide bonds, causing the enzyme molecules to partially unfold. 4) The compound is a negative allosteric regulator. 5) The compound causes a cofactor to be lost from the enzyme.

1

What is the free energy change (ΔG) of the hydrolysis of ATP to ADP? 1) The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi may vary considerably with variations in pH, temperature, atmospheric pressure, and concentrations of reactants and products. 2) The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is constant at -7.3 kcal/mole. 3) The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is approximately -7.3 kcal/mole, but it varies from species to species

1

Which of the following is most similar in structure to ATP? 1) an RNA nucleotide 2) a pentose sugar 3) a DNA nucleotide 4) a phospholipid 5) an amino acid with three phosphate groups attached

1

Which of the following statements is representative of the second law of thermodynamics? 1) Cells require a continuous input of energy to maintain their high level of organization. 2) Heat represents a form of energy that can be used by most organisms to do work. 3) Every energy transformation by a cell decreases the entropy of the universe. 4) Conversion of energy from one form to another is always accompanied by some gain of free energy. 5) Without an input of energy, organisms would tend toward decreasing entropy.

1

Which of the following would increase the rate of the reverse reaction? 1) increasing the concentration of ammonia 2) decreasing the temperature 3) increasing the concentration of nitrogen

1

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) 1) cofactor necessary for enzyme activity. 2) noncompetitive inhibitor of the enzyme. 3) competitive inhibitor of the enzyme. 4) coenzyme derived from a vitamin. 5) allosteric activator of the enzyme.

1

Select the highest energy form of adenosine from the following images. 1) The figure shows the structure which consists of adenine, ribose molecule, and 3 phosphate residues attached to ribose molecule. 2) The figure shows the structure which consists of adenine, ribose molecule, and 2 phosphate residues attached to ribose molecule. 3) The figure shows the structure which consists of adenine, ribose molecule, and a phosphate residue attached to the ribose molecule. 4) The figure shows the structure which consists of adenine and ribose molecules. 5) The figure shows the structure which consists of ribose molecule and 3 phosphate residues.

1 (ATP)

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 A as it binds to the enzyme? 1) an intermediate 2) a substrate 3) an allosteric inhibitor 4) a coenzyme 5) the product

2

A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because 1) starch cannot be hydrolyzed in the presence of so much water. 2) the activation energy barrier for this reaction cannot easily be surmounted at room temperature. 3) the starch solution has less free energy than the sugar solution. 4) the hydrolysis of starch to sugar is endergonic. 5) starch hydrolysis is nonspontaneous.

2

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously? 1) Heat is being used by the organism as a source of energy. 2) Energy input into the organism must be occurring to drive the decrease in entropy. 3) The entropy of the organism's environment must also be decreasing. 4) In this situation, the second law of thermodynamics must not apply. 5) The first law of thermodynamics is being violated.

2

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? 1) It is a noncompetitive inhibitor. 2) It is a competitive inhibitor. 3) It is able to bind to succinate. 4) It is an allosteric regulator. 5) It blocks the binding of fumarate.

2

The Haber process is typically carried out at a temperature of approximately 500∘C. What would happen to the rate of the forward reaction if the temperature were lowered to 100∘C? 1) increase 2) decrease

2

The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs? 1) The allosteric inhibitor lowers the temperature of the active site. 2) The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site. 3) The allosteric inhibitor causes free energy change of the reaction to increase. 4) The allosteric inhibitor binds to the active site, preventing the substrate from binding. 5) The allosteric inhibitor binds to the substrate and prevents it from binding at the active site.

2

What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased? 1) increase 2) decrease

2

Which of the following is true of metabolism in its entirety in all organisms? 1) Metabolism depends on a constant supply of energy from food. 2) Metabolism consists of all the energy transformation reactions in an organism. 3) Metabolism manages the increase of entropy in an organism. 4) Metabolism depends on an organism's adequate hydration. 5) Metabolism uses all of an organism's resources.

2

Which of the following statements about feedback regulation of a metabolic pathway is correct? 1) Accumulation of the product of the pathway increases further formation of that product. 2) The final product of a metabolic pathway is usually the compound that regulates the pathway. 3) The compound that regulates the pathway acts as a competitive inhibitor or a positive allosteric regulator. 4) The enzyme that is regulated by feedback inhibition is usually the last enzyme in the metabolic pathway. 5) The products of the pathway become the reactants for a different reaction, and thus products are unable to accumulate.

2

Which of the following statements regarding enzymes is true? 1) Enzymes make the rate of a reaction independent of substrate concentrations. 2) Enzymes increase the rate of a reaction by lowering the activation energy barrier. 3) Enzymes increase the rate of a reaction by making the reaction more exergonic. 4) Enzymes increase the rate of a reaction by reducing the rate of reverse reactions. 5) Enzymes change the equilibrium point of the reactions they catalyze.

2

Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction? 1) Increase the pH. 2) Increase the temperature. 3) Increase the enzyme concentration. 4) Increase the substrate concentration.

3

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the G for the new reaction? 1) +20 kcal/mol 2) 0 kcal/mol 3) -20 kcal/mol 4) -40 kcal/mol 5) +40 kcal/mol

3

How does an enzyme increase the rate of the chemical reaction it catalyzes? 1) An enzyme reduces the free-energy change (ΔG) of the reaction it catalyzes. 2) An enzyme's active site binds only the reactants, and not the products of a reaction, pushing the equilibrium for the reaction far to the right. 3) An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes.

3

If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur? 1) The free energy of the system will change. 2) Additional product will be formed. 3) Nothing; the reaction will stay at equilibrium. 4) Additional substrate will be formed. 5) The reaction will change from endergonic to exergonic.

3

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. Based on this information, which of the following is correct? 1) Malonic acid is the product, and fumarate is a competitive inhibitor. 2) Succinate dehydrogenase is the enzyme, and fumarate is the substrate. 3) Succinate is the substrate, and fumarate is the product. 4) Fumarate is the product, and malonic acid is a noncompetitive inhibitor. 5) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate.

3

Under most conditions, the supply of energy by catabolic pathways is regulated by the demand for energy by anabolic pathways. Considering the role of ATP formation and hydrolysis in energy coupling of anabolic and catabolic pathways, which of the following statements is most likely to be true? 1) High levels of ATP act as an allosteric activator of catabolic pathways. 2) High levels of ADP act as an allosteric inhibitor of anabolic pathways. 3) High levels of ADP act as an allosteric activator of catabolic pathways 4) High levels of ATP act as an allosteric activator of anabolic pathways. 5) High levels of ADP act as an allosteric inhibitor of catabolic pathways.

3

Which of the following is (are) true for anabolic pathways? 1) They consume energy to decrease the entropy of the organism and its environment. 2) They do not depend on enzymes. 3) They consume energy to build up polymers from monomers. 4) They are usually highly spontaneous chemical reactions. 5) They release energy as they degrade polymers to monomers.

3

Which of the following reactions would be endergonic? 1) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O 2) HCl → H+ + Cl- 3) glucose + fructose → sucrose 4) ATP → ADP + Pi 5) All of the listed responses are correct.

3

Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown? 1) P0 binds E4 and activates it. 2) P2 binds E2 and activates it. 3) P4 binds E1 and deactivates it. 4) P3 binds E2 and activates it 5) P4 binds E3 and deactivates it.

3

Which of the following statements is true concerning catabolic pathways? 1) They are endergonic. 2) They are spontaneous and do not need enzyme catalysis. 3) They supply energy, primarily in the form of ATP, for the cell's work. 4) They build up complex molecules such as protein from simpler compounds. 5) They combine molecules into more energy-rich molecules.

3

Which of these is ATP? 1) The figure shows the molecule, which consists of three phosphate groups, deoxyribose, and nitrogenous base guanine. 2) The figure shows the molecule, which consists of two phosphate groups, ribose, and nitrogenous base adenine. 3) The figure shows the molecule, which consists of three phosphate groups, ribose, and nitrogenous base adenine. 4) The figure shows the molecule, which consists of three phosphate groups, ribose, and nitrogenous base thymine. 5) The figure shows the molecule, which consists of three phosphate groups, deoxyribose, and nitrogenous base adenine.

3

Which statement about the binding of enzymes and substrates is correct? 1) Substrate molecules bind to the active site of the enzyme only by weak bonds, such as hydrogen bonds or hydrophobic attraction. 2) Substrate molecules fit into the active site of an enzyme like a key fits into a lock. 3) When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.

3

Why is ATP an important molecule in metabolism? 1) Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free energy. 2) It is one of the four building blocks for DNA synthesis. 3) It provides energy coupling between exergonic and endergonic reactions. 4) Its terminal phosphate bond has higher energy than the other two. 5) Its hydrolysis provides an input of free energy for exergonic reactions.

3

Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy? 1) the heat released from a living organism: potential energy 2) the energy related to the height of a bird above the ground: kinetic energy 3) the energy associated with a gradient of ions across a membrane: kinetic energy 4) the covalent bonds of a sugar molecule: potential energy 5) the motion of individual molecules: potential energy

4

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to 1) add an allosteric inhibitor. 2) heat the solution to 90°C. 3) add a noncompetitive inhibitor. 4) add more of the enzyme. 5) add more substrate.

4

Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? 1) Heat produced by the organism is conserved in the organism and not lost to the environment. 2) Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy. 3) The metabolism of an organism is isolated from its surroundings. 4) Organisms acquire energy from, and lose energy to, their surroundings. 5) All of the listed responses are correct.

4

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? 1) They flip back and forth across the membrane to access target proteins on either side. 2) They require phospholipids as a cofactor. 3) ATP is more abundant near the plasma membrane. 4) They can more readily encounter and phosphorylate other membrane proteins. 5) Membrane localization lowers the activation energy of the phosphorylation reaction.

4

The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as 1) allosteric inhibition. 2) noncooperative inhibition. 3) metabolic inhibition. 4) feedback inhibition. 5) reversible inhibition.

4

Which of the following correctly states the relationship between anabolic and catabolic pathways? 1) Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. 2) Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules. 3) Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways. 4) Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. 5) The flow of energy between catabolic and anabolic pathways is reversible.

4

Which of the following is true for all exergonic reactions? 1) The products have more total energy than the reactants. 2) The reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted to reactants. 3) The reactions are rapid. 4) The reaction proceeds with a net release of free energy. 5) A net input of energy from the surroundings is required for the reactions to proceed.

4

Which of the following states the relevance of the first law of thermodynamics to biology? 1) Photosynthetic organisms produce energy in sugars from sunlight. 2) Energy is destroyed as glucose is broken down during cellular respiration 3) The total energy taken in by an organism must be greater than the total energy stored or released by the organism. 4) Energy can be freely transformed among different forms as long as the total energy is conserved. 5) Living organisms must increase the entropy of their surroundings.

4

Which term most precisely describes the cellular process of breaking down large molecules into smaller ones? 1) catalysis 2) metabolism 3) anabolism 4) catabolism 5) dehydration

4

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 1) a coenzyme. 2) the substrate. 3) a competitive inhibitor. 4) an intermediate. 5) an allosteric inhibitor.

5

Enzyme activity is affected by pH because _____. 1) most substrates don't function well at high or low pH 2) the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier 3) low pH will denature all enzymes 4) changes in pH can cause loss of cofactors from the enzyme 5) high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

5

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? 1) Living organisms do not obey the second law of thermodynamics, which states that entropy must increase with time. 2) Living organisms do not follow the laws of thermodynamics. 3) Living organisms are able to transform energy into entropy. 4) 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. 5) As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.

5

When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell? 1) It is added to water and excreted as a liquid. 2) It is secreted as waste. 3) It enters the nucleus and affects gene expression. 4) It is used only to regenerate more ATP. 5) It may be used to form a phosphorylated intermediate.

5

Which of the following environments or actions would not affect the rate of an enzyme reaction? 1) substrate concentration 2) cooling the enzyme 3) pH 4) heating the enzyme 5) None of the listed responses is correct.

5

Which of the following has the most free energy per molecule? 1) a sugar molecule 2) a fatty acid molecule 3) an amino acid molecule 4) a cholesterol molecule 5) a starch molecule

5

Which of the following statements about equilibrium of chemical reactions is correct? 1) The equilibrium point of a reaction represents the least stable configuration for that reaction. 2) The equilibrium point is where the system has the highest free energy 3) Most reactions in a living cell are close to equilibrium. 4) Reactions can only go in the direction toward equilibrium. 5) A reaction that is at equilibrium is not capable of doing any work.

5

Which of the following would be unlikely to contribute to the substrate specificity of an enzyme? 1) A hydrophobic group on the substrate interacts with several hydrophobic amino acids on the enzyme. 2) A positive charge on the substrate is attracted to a negative charge in the active site of the enzyme. 3) A similar shape exists between a pocket on the surface of the enzyme and a functional group on the substrate. 4) The enzyme has the ability to change its configuration in response to the substrate binding. 5) The enzyme has an allosteric regulatory site.

5