Biology Chapter 8 Practice Test
Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) TΔS ΔS ΔG ΔH All of these values reveal the direction in which a reaction will go.
ΔG
Which of the following statements about allosteric proteins is/are true? (see book section: Concept 8.5: Regulation of enzyme activity helps control metabolism) They exist in active and inactive conformations. They are acted on by inhibitors. They are sensitive to environmental conditions. All of the first three listed responses are correct. None of the first three listed responses is correct.
All of the first three listed responses are correct.
Which of the following statements about enzymes is INCORRECT? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) Enzymes can be used to accelerate both anabolic and catabolic reactions. Most enzymes are proteins. An enzyme is consumed during the reaction it catalyzes. An enzyme lowers the activation energy of a chemical reaction. An enzyme is very specific in terms of the substrate to which it binds.
An enzyme is consumed during the reaction it catalyzes.
Which of the following metabolic processes can occur without a net influx of energy from some other process? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O amino acids → protein 6 CO2 + 6 H2O → C6H12O6 + 6 O2 ADP + (p) i → ATP + H20 glucose + fructose → sucrose
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Which of the following correctly states the relationship between anabolic and catabolic pathways? (see book section: Concept 8.1: An organism's metabolism transforms matter and energy, subject to the laws of thermodynamics) A. The flow of energy between catabolic and anabolic pathways is reversible. B. Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. C. Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways. D. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. E. Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules.
D. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.
Which of the following states the relevance of the first law of thermodynamics to biology? (see book section: Concept 8.1: An organism's metabolism transforms matter and energy, subject to the laws of thermodynamics) Energy can be freely transformed among different forms as long as the total energy is conserved. Energy is destroyed as glucose is broken down during cellular respiration Because living things consume energy, the total energy of the universe is constantly decreasing. Living organisms must increase the entropy of their surroundings. Photosynthetic organisms produce energy in sugars from sunlight.
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? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) The entropy of the organism's environment must also be decreasing. The first law of thermodynamics is being violated. In this situation, the second law of thermodynamics must not apply. Heat is being used by the organism as a source of energy. Energy input into the organism must be occurring to drive the decrease in entropy.
Energy input into the organism must be occurring to drive the decrease in entropy.
Which of the following statements about enzyme function is correct? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output. Enzymes can greatly speed up reactions, but they cannot change the activation energy because they cannot change the net energy output. Enzymes can greatly speed up reactions, but they cannot change the net energy output because they cannot change the activation energy. Enzymes can change the equilibrium point of reactions, but they cannot speed up reactions because they cannot change the net energy output. 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/are true? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) The more heat that is added to a reaction, the faster the enzymes will function. Enzymes speed up the rate of the reaction without changing the DG for the reaction. Enzymes increase the rate of a reaction by raising the activation energy for reactions. Enzymes react with their substrate (form chemical bonds), forming an enzyme-substrate complex, which irreversibly alters the enzyme. All of the listed responses are correct
Enzymes speed up the rate of the reaction without changing the DG for the reaction.
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? (see book section: Concept 8.5: Regulation of enzyme activity helps control metabolism) High levels of ATP result in allosteric activation of catabolic pathways. High levels of ADP result in allosteric inhibition of anabolic pathways. High levels of ATP result in allosteric activation of anabolic pathways. High levels of ADP result in allosteric inhibition of catabolic pathways. High levels of ADP result in allosteric activation of catabolic pathways.
High levels of ADP result in allosteric activation of catabolic pathways.
When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations? (see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) In the cell, the hydrolysis of ATP is coupled to other endergonic reactions. The amount of heat released by a reaction has nothing to do with the free energy change of the reaction. Cells have the ability to store heat; this cannot happen in a test tube. In cells, ATP is hydrolyzed to ADP and Pi, but in the test tube it is hydrolyzed to carbon dioxide and water. Cells are less efficient at energy metabolism than reactions that are optimized in a test tube.
In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.
What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously and see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) The more negative the ΔG, the faster the reaction is. Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction. The sign does not matter, but the larger the magnitude of ΔG, the faster the reaction. The sign does not matter, but the smaller the magnitude of ΔG, the faster the reaction. The sign determines whether the reaction is spontaneous, and the magnitude determines the speed.
Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction.
Which of the following environments or actions would NOT affect the rate of an enzyme reaction? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) pH substrate concentration heating the enzyme cooling the enzyme None of the listed responses is correct.
None of the listed responses is correct.
If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur? Additional substrate will be formed. The free energy of the system will change. The reaction will change from endergonic to exergonic. Nothing; the reaction will stay at equilibrium. Additional product will be formed.
Nothing; the reaction will stay at equilibrium.
Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? (see book section: Concept 8.1: An organism's metabolism transforms matter and energy, subject to the laws of thermodynamics) Organisms acquire energy from, and lose energy to, their surroundings. Heat produced by the organism is conserved in the organism and not lost to the environment. Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy. The metabolism of an organism is isolated from its surroundings. All of the listed responses are correct.
Organisms acquire energy from, and lose energy to, their surroundings.
Succinylcholine is structurally almost identical to acetylcholine. If succinylcholine is added to a mixture that contains acetylcholine and the enzyme that hydrolyzes acetylcholine (but not succinylcholine), the rate of acetylcholine hydrolysis is decreased. Subsequent addition of more acetylcholine restores the original rate of acetylcholine hydrolysis. Which of the following correctly explains this observation? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) The active site must have the wrong configuration to permit succinylcholine binding. The presence of succinylcholine changes the conditions in the solution, resulting in a denaturation of the enzyme. Succinylcholine must be an allosteric regulator for this enzyme. Succinylcholine must be a competitive inhibitor with acetylcholine. Succinylcholine must be a noncompetitive inhibitor.
Succinylcholine must be a competitive inhibitor with acetylcholine.
Which of these statements about enzyme inhibitors is true? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback. Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory. A noncompetitive inhibitor does not change the shape of the active site. A competitive inhibitor binds to the enzyme at a place that is separate from the active site. The action of competitive inhibitors may be reversible or irreversible.
The action of competitive inhibitors may be reversible or irreversible.
Which of the following statements about the active site of an enzyme is correct? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) The active site has a fixed structure (shape). The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits. The structure of the active site is not affected by changes in temperature. Coenzymes are rarely found in the active site of an enzyme. The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme.
The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.
Which of the following is an example of the second law of thermodynamics as it applies to biological reactions? (see book section: Concept 8.1: An organism's metabolism transforms matter and energy, subject to the laws of thermodynamics) The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water. All types of cellular respiration produce ATP. Cellular respiration releases some energy as heat. The first and second choices are correct. The first, second, and third choices are correct.
The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.
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? (see book section: Concept 8.5: Regulation of enzyme activity helps control metabolism) The allosteric inhibitor binds to the substrate and prevents it from binding at the active site. The allosteric inhibitor binds to the active site, preventing the substrate from binding. The allosteric inhibitor lowers the temperature of the active site. The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site. The allosteric inhibitor causes free energy change of the reaction to increase.
The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.
According to the second law of thermodynamics, which of the following is true? (see book section: Concept 8.1: An organism's metabolism transforms matter and energy, subject to the laws of thermodynamics) All reactions produce some heat. Energy conversions increase the order in the universe. The entropy of the universe is constantly decreasing. The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists. The total amount of energy in the universe is constant.
The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists.
What is meant by the "induced fit" of an enzyme? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) The shape of the active site is nearly perfect for specifically binding the enzyme's substrate or substrates. The enzyme changes its shape slightly as the substrate binds to it. The substrate can be altered so that it is induced to fit into the enzyme's active site. The presence of the substrate in solution induces the enzyme to slightly change its structure. The enzyme structure is altered so that it can be induced to fit many different types of substrate.
The enzyme changes its shape slightly as the substrate binds to it.
Which of the following statements correctly describe(s) the role or roles of heat in biological reactions? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) Heat from the environment is necessary for substrates to get over the activation energy barrier. The kinetic energy of the substrates is increased as the amount of heat in the system is increased. Increasing the amount of heat in a system will always increase the rate of enzyme-catalyzed reactions. The first and second choices are correct. The second and third choices are correct.
The first and second choices are correct.
Above a certain substrate concentration, the rate of an enzyme-catalyzed reaction drops as the enzymes become saturated. Which of the following would lead to a faster conversion of substrate into product under these saturated conditions? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) an increase in concentration of enzyme increasing the temperature by a few degrees increasing the substrate concentration The first and second listed responses are correct. The first, second, and third listed responses are correct.
The first and second listed responses are correct.
Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend(s) to keep these pathways away from equilibrium? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) the continuous removal of the products of a pathway to be used in other reactions an input of free energy from outside the pathway an input of heat from the environment The first and second listed responses are correct. The first, second, and third listed responses are correct.
The first and second listed responses are correct.
Which of the following best characterizes the role of ATP in cellular metabolism? (see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) The DG associated with its hydrolysis is positive. The charge on the phosphate group of ATP tends to make the molecule very water-soluble. It is catabolized to carbon dioxide and water. The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate. The release of free energy during the hydrolysis of ATP heats the surrounding environment.
The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.
Molecules A and B contain 110 kcal/mol of free energy, and molecules B and C contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) The conversion of A and B to C and D is spontaneous. The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants. The entropy in the products, C and D, is higher than in the reactants, A and B. A and B will be converted to C and D with a net release of energy. The conversion of A and B to C and D is exergonic; the products are less organized than the reactants.
The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants.
Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell AGAINST the ion's concentration gradient? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously and see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) Neither ATP hydrolysis nor active transport is spontaneous. The hydrolysis of ATP is endergonic, and the active transport is exergonic. ATP is acting as a transport protein to facilitate the movement of the ion across the plasma membrane. This is an example of energy coupling. Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system.
This is an example of energy coupling.
Consider the growth of a farmer's crop over a season. Which of the following correctly states a limitation imposed by the first or second law of thermodynamics? (see book section: Concept 8.1: An organism's metabolism transforms matter and energy, subject to the laws of thermodynamics) To obey the first law, the crops must represent an open system. The process of photosynthesis produces energy that the plant uses to grow. The entropy of the universe must decrease to account for the increased entropy associated with plant growth. Growth of the crops must occur spontaneously. All of the listed responses are correct.
To obey the first law, the crops must represent an open system.
From the equation ΔG = ΔH - TΔS it is clear that __________. (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) increasing the temperature of a system will increase the probability of spontaneous change increasing the entropy of a system will increase the probability of spontaneous change a decrease in the system's total energy will increase the probability of spontaneous change a decrease in the system's total energy will increase the probability of spontaneous change, and increasing the entropy of a system will increase the probability of spontaneous change a decrease in the system's total energy will increase the probability of spontaneous change, increasing the entropy of a system will increase the probability of spontaneous change, and increasing the temperature of a system will increase the probability of spontaneous change
a decrease in the system's total energy will increase the probability of spontaneous change, increasing the entropy of a system will increase the probability of spontaneous change, and increasing the temperature of a system will increase the probability of spontaneous change
Which of the following has the most free energy per molecule? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) a starch molecule a sugar molecule a fatty acid molecule a cholesterol molecule an amino acid molecule
a starch molecule
If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to heat the solution to 90°C. add a noncompetitive inhibitor. add more substrate. add an allosteric inhibitor. add more of the enzyme.
add more of the enzyme.
The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule outside the active site is an example of __________. (see book section: Concept 8.5: Regulation of enzyme activity helps control metabolism) competitive inhibition feedback inhibition cooperativity noncompetitive inhibition allosteric activation
allosteric activation
How do enzymes lower activation energy? (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) by increasing reactivity of products by locally concentrating the reactants by harnessing heat energy to drive the breakage of bonds between atoms The first two responses are correct. The second and third choices are correct.
by locally concentrating the reactants
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _______ is to _______. free energy; entropy exergonic; endergonic entropy; enthalpy exergonic; spontaneous work; energy
exergonic; endergonic
Which of the following reactions would be endergonic? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) ATP → ADP + Pi HCl → H+ + Cl- glucose + fructose → sucrose C6H12O6 + 6 O2 → 6 CO2 + 6 H2O All of the listed responses are correct.
glucose + fructose → sucrose
Enzyme activity is affected by pH because __________. (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier most substrates do not function well at high or low pH low pH will denature all enzymes changes in pH can cause loss of cofactors from the enzyme
high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site
The free energy derived from the hydrolysis of ATP can be used to perform many kinds of cellular work. Which of the following is an example of the cellular work involved in the production of electrochemical gradients? (see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) the beating of cilia the chemical synthesis of ATP proton movement against a gradient of protons facilitated diffusion chromosome movement on microtubules
proton movement against a gradient of protons
An exergonic (spontaneous) reaction is a chemical reaction that __________. (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) is common in anabolic pathways leads to a decrease in the entropy of the universe occurs only when an enzyme or other catalyst is present releases energy when proceeding in the forward direction cannot occur outside of a living cell
releases energy when proceeding in the forward direction
In general, the hydrolysis of ATP drives cellular work by __________. (see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) releasing free energy that can be coupled to other reactions releasing heat acting as a catalyst changing to ADP and phosphate lowering the activation energy of the reaction
releasing free energy that can be coupled to other reactions
Most cells cannot harness heat to perform work because cells do not have much heat; they are relatively cool. heat can never be used to do work. temperature is usually uniform throughout a cell. heat is not a form of energy. heat must remain constant during work.
temperature is usually uniform throughout a cell.
Which of the following is changed by the presence of an enzyme in a reaction? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously and see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) the G value for the reactants the magnitude of ΔG the G value for the products the activation energy the sign of ΔG
the activation energy
Which of the following determines the sign of ΔG for a reaction? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) the free energy of the reactants the enzyme catalyzing the reaction's having a low affinity for the products the enzyme catalyzing the reaction's having a high affinity (strength of binding) for the reactants the free energy of the products the free energy of the reactants and the free energy of the products
the free energy of the reactants and the free energy of the products
The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways? (see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) the hydrolysis of ATP the conversion of glucose + fructose to make sucrose the formation of ATP from ADP + Pi the contraction of a muscle cell the active transport of a phosphate ion into the cell
the hydrolysis of ATP
Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because __________. (see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions) the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP the bonds between the phosphate groups are unusually strong and breaking them releases free energy the phosphate groups are polar and are attracted to the water in the cell's interior the valence electrons in the phosphorus atom have less energy on average than those of other atoms they are hydrogen bonds, which are only about 10% as strong as covalent bonds
the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP
A chemical reaction is designated as exergonic rather than endergonic when __________. (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously and see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) the products are less complex than the reactants the potential energy of the products is less than the potential energy of the reactants activation energy is required it absorbs more energy activation energy exceeds net energy release
the potential energy of the products is less than the potential energy of the reactants
Some bacteria are metabolically active in hot springs because their enzymes are completely insensitive to temperature. they use molecules other than proteins or RNAs as their main catalysts. high temperatures make catalysis unnecessary. they are able to maintain a lower internal temperature. their enzymes have high optimal temperatures.
their enzymes have high optimal temperatures.
A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that __________. (see book section: Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers) the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme the enzyme was denatured there is too little activation energy available the hydrogen bonds that define the structure of the enzyme's active site are unstable the substrate becomes a competitive inhibitor at lower temperature
there is too little activation energy available
If, during a process, the system becomes more ordered, then __________. (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) ΔH is negative ΔG is negative ΔS is negative ΔH is positive ΔG is positive
ΔS is negative
When one molecule is broken down into six component molecules, which of the following will always be true? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously) ΔG is positive. An input of free energy is needed. ΔS is positive. ΔS is negative. ΔH is negative.
ΔS is positive.