Chapter 8

As ATP begins to build up in a cell, metabolism slows down. How does this happen?

ATP acts as an allosteric inhibitor to many of the enzymes involved in metabolism, thus slowing their function.

Which of the following correctly states the relationship between anabolic and catabolic pathways? A. The flow of energy between catabolic and anabolic pathways is reversible. B. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. C. Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. D. Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways. E. Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules.

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

At low temperatures, a particular enzyme catalyzes a reaction, but at a slow rate. At high temperatures, the enzyme is completely inactive. What statement best explains the difference in how temperature affects the function of this enzyme?

At low temperatures, there is not enough free energy for the enzyme to function at a high rate, and at high temperatures, the enzyme is denatured, leaving it nonfunctional.

Which of the following statements correctly describes cofactors and coenzymes? A. Both are nonprotein enzyme helpers; but most coenzymes are metal ions, and most cofactors are organic molecules. B. Both cofactors and coenzymes act as allosteric inhibitors to various enzymes. C. Neither cofactors nor coenzymes assist enzyme function. D. Cofactors that are metal ions activate enzymes, but coenzymes deactivate them. E. Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.

Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.

How does ATP drive mechanical work inside a cell?

By binding to motor proteins

How does ATP drive transport work inside a cell?

By phosphorylating a transport protein

Which of the following statements is correct regarding competitive and noncompetitive enzyme inhibitors? A. Inhibitors always bind irreversibly to an enzyme. B. Competitive inhibitors do not bind directly to the active site of an enzyme while noncompetitive inhibitors do. C. Only competitive inhibitors affect enzyme function. D. Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site. E. Neither type of inhibitor affects enzyme function.

Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site.

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

Energy can be freely transformed among different forms as long as the total energy is conserved.

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously?

Energy input into the organism must be occurring to drive the decrease in entropy.

Which of the following statements about enzyme function is correct? A. Enzymes can greatly speed up reactions, but they cannot change the activation energy because they cannot change the net energy output. B. Enzymes can change the equilibrium point of reactions, but they cannot speed up reactions because they cannot change the net energy output. C. Enzymes can greatly speed up reactions, but they cannot change the net energy output because they cannot change the activation energy. D. Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output. E. None of the listed responses is correct.

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.

Which of the following statements about enzymes is true? A. All of the listed responses are correct. B. Enzymes increase the rate of a reaction by raising the activation energy for reactions. C. Enzymes speed up the rate of the reaction without changing the ΔG for the reaction. D. The more heat that is added to a reaction, the faster the enzymes will function. E. Enzymes react with their substrate (form chemical bonds), forming an enzyme-substrate complex, which irreversibly alters the enzyme.

Enzymes speed up the rate of the reaction without changing the ΔG for the reaction.

The primary manner in which cells manage their energy resources in order to do work is called energy coupling. Which of the following statements accurately defines energy coupling? A. Chemical reactions in cells are always at equilibrium. B. Endergonic and exergonic reactions occur independently of each other. C. Exergonic reactions drive endergonic reactions. D. Endergonic reactions drive exergonic reactions. E. Anabolic reactions drive catabolic reactions.

Exergonic reactions drive endergonic reactions.

Which of the following reactions would be endergonic? A. HCl → H+ + Cl B. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O C. ATP → ADP + Pi D. Glucose + fructose → sucrose E. All of the listed responses are correct.

Glucose + fructose → sucrose

Which of the following statements is correct regarding kinetic and potential energy? A. Chemical energy is a type of kinetic energy, and thermal energy is a type of potential energy. B. Kinetic energy is associated with the relative motion of objects, and potential energy is the energy that matter possesses because of its location or structure. C. None of the listed responses is correct. D. Potential energy is related to the relative motion of objects, and kinetic energy is the energy that matter possesses because of its location or structure. E. Potential energy cannot be converted to kinetic energy.

Kinetic energy is associated with the relative motion of objects, and potential energy is the energy that matter possesses because of its location or structure.

Which of the following is true regarding metabolic pathways? A. Metabolic pathways are not important to a cell's ability to function. B. Metabolic pathways consist of only anabolic pathways. C. Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme. D. Each reaction in the pathway is catalyzed by the same enzyme. E. Metabolic pathways consist of a single chemical reaction.

Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme.

What would the value of ΔS be for a chemical reaction in which a molecule is broken down into smaller components?

Positive

Which of these statements about enzyme inhibitors is true? A. The action of inhibitors may be reversible or irreversible. B. A noncompetitive inhibitor does not change the shape of the active site. C. A competitive inhibitor binds to the enzyme at a place that is separate from the active site. D. Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory. E. When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.

The action of inhibitors may be reversible or irreversible.

Which of the following is changed by the presence of an enzyme in a reaction? A. The sign of ΔG B. The magnitude of ΔG C. The G value for the reactants D. The activation energy E. The G value for the products

The activation energy

Which of the following is an example of the second law of thermodynamics as it applies to biological reactions? A. None of the listed responses is correct. B. All of the listed responses are correct. C. Cellular respiration releases some energy as heat. D. The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water. E. All types of cellular respiration produce ATP.

The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.

Which of the following statements is correct regarding ATP? A. ATP cannot transfer energy to other molecules. B. The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups. C. ATP molecules do not release free energy when hydrolyzed. D. The energy in an ATP molecule is released from the ribose group. E. The energy in an ATP molecule is released from the adenine group.

The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups.

At low pH, a particular enzyme catalyzes a reaction at a high rate. At neutral pH, the enzyme is completely inactive. What statement best explains the difference in how pH affects the function of this enzyme?

The enzyme is adapted for low pH but is denatured at neutral pH, leaving it nonfunctional.

What best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis that may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of __________.

allosteric regulation

ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________.

feedback inhibition

Enzyme activity is affected by pH because __________.

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

An exergonic (spontaneous) reaction is a chemical reaction that __________.

releases energy when proceeding in the forward direction

An exergonic reaction __________ free energy, and an endergonic reaction __________ free energy.

releases; absorbs

In general, the hydrolysis of ATP drives cellular work by __________.

releasing free energy that can be coupled to other reactions

Which of the following statements about the active site of an enzyme is correct? A. The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme. B. The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits. C. The active site has a fixed structure (shape). D. Coenzymes are rarely found in the active site of an enzyme. E. The structure of the active site is not affected by changes in temperature.

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.