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