Campbell Biology Chapter 8 review
The study of energy flow through a living organism defines... a. metabolism b. catabolism c. anabolism d. bioernergetics e. none of the above are correct
bioernergetics
Which of the following is the most correct interpretation of the figure? a. Inorganic phosphate is created from organic phosphate b. Energy from catabolism can be used directly for performing cellular work c. ADP + Pi are a set of molecules that store energy for catabolism d. ATP is a molecule that acts as an intermediary to store energy for cellular work e. Pi acts as a shuttle molecule to move energy from ATP to ADP
ATP is a molecule that acts as an intermediary to store energy for cellular work
How can one increase the rate of a chemical reaction? a. Increase the activation energy needed b. Cool the reactants c. Decrease the concentration of the reactants d. Add a catalyst e. Increase the entropy of the reactants
Add a catalyst
Which of the following statements about allosteric proteins is/are true? a. They are acted on by inhibitors b. They exist in active and inactive conformations c. They are sensitive to environmental conditions d. All of the first three listed responses are correct e. 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? a. An enzyme lowers the activation energy of a chemical reaction b. Enzymes can be used to accelerate both anabolic and catabolic reactions c. An enzyme is consumed during the reaction it catalyzes d. An enzyme is very specific in terms of the substrate to which it binds e. Most enzymes are proteins
An enzyme is consumed during the reaction it catalyzes If enzymes were consumed during the reaction they catalyzed, they would not be able to act as a catalyst. This statement is incorrect.
Which of the following correctly states the relationship between anabolic and catabolic pathways? a. Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways b. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways c. The flow of energy between catabolic and anabolic pathways is reversible d. Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules e. Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways
Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways The synthesis of complex molecules in anabolic pathways requires an input of energy from catabolic pathways.
Which of the following metabolic processes can occur without a net influx of energy from some other process? a. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O b. 6 CO2 + 6 H2O → C6H12O6 + 6 O2 c. amino acids → protein d. ADP + i → ATP + H2O e. glucose + fructose → sucrose
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Which of the following states the relevance of the first law of thermodynamics to biology? a. Energy is destroyed as glucose is broken down during cellular respiration b. Photosynthetic organisms produce energy in sugars from sunlight c. Living organisms must increase the entropy of their surroundings d. Energy can be freely transformed among different forms as long as the total energy is conserved e. Because living things consume energy, the total energy of the universe is constantly decreasing
Energy can be freely transformed among different forms as long as the total energy is conserved The first law of thermodynamics states that energy can be transformed but can be neither created nor destroyed.
If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously? a. The entropy of the organism's environment must also be decreasing b. The first law of thermodynamics is being violated c. In this situation, the second law of thermodynamics must not apply d. Heat is being used by the organism as a source of energy e. 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 If the entropy is decreasing, this would tend to make the free energy change associated with this positive. Thus, an input of energy would be required to make this decrease in entropy occur.
Which of the following statements about enzyme function is correct? a. Enzymes can greatly speed up reactions, but they cannot change the net energy output because they cannot change the activation energy 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 change the equilibrium point of reactions, but they cannot speed up reactions because they cannot change the net energy output 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 Enzymes lower the activation energy barrier of a reaction but do not change the free energy of the products.
Which of the following statements about enzymes is/are true? a. Enzymes react with their substrate (form chemical bonds), forming an enzyme-substrate complex, which irreversibly alters the enzyme b. Enzymes increase the rate of a reaction by raising the activation energy for reactions c. The more heat that is added to a reaction, the faster the enzymes will function d. Enzymes speed up the rate of the reaction without changing the ΔG for the reaction e. All of the listed responses are correct
Enzymes speed up the rate of the reaction without changing the ΔG for the reaction Enzymes speed up reactions by lowering the activation energy barrier for the reaction. Enzymes cannot change the DG for the reaction.
Living organisms would be examples of isolated systems. a. True b. False
False
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 ADP result in allosteric inhibition of anabolic pathways b. High levels of ATP result in allosteric activation of anabolic pathways c. High levels of ADP result in allosteric inhibition of catabolic pathways d. High levels of ATP result in allosteric activation of catabolic pathways e. High levels of ADP result in allosteric activation of catabolic pathways
High levels of ATP 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? a. Cells are less efficient at energy metabolism than reactions that are optimized in a test tube b. In the cell, the hydrolysis of ATP is coupled to other endergonic reactions c. Cells have the ability to store heat; this cannot happen 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 cells, ATP is hydrolyzed to ADP and Pi, but in the test tube it is hydrolyzed to carbon dioxide and water
In the cell, the hydrolysis of ATP is coupled to other endergonic reactions The coupling of ATP to other endergonic processes in cells means that less of the free energy is released as heat. When ATP is hydrolyzed without this coupling, all of the energy is released as heat.
It is possible to transform kinetic energy into potential energy and visa versa. a. True b. False
True
What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction? a. The sign determines whether the reaction is spontaneous, and the magnitude determines the speed b. Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction c. The more negative the ΔG, the faster the reaction is d. The sign does not matter, but the larger the magnitude of ΔG, the faster the reaction e. The sign does not matter, but the smaller the magnitude of ΔG, the faster the reaction
Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction The speed of a reaction is determined by the activation energy barrier of the reaction and the temperature (which determines how many reactants have the energy to overcome the barrier).
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
None of the listed responses is correct Changes in temperature, substrate concentration, and pH are all likely to affect enzyme activity.
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. Additional substrate will be formed c. The free energy of the system will change d. Nothing; the reaction will stay at equilibrium e. The reaction will change from endergonic to exergonic
Nothing; the reaction will stay at equilibrium
If an enzyme is added to a solution where its substrate and product are in equilibrium, what would occur? a. Additional product would be formed b. Additional substrate would be formed c. The reaction would change from endergonic to exergonic d. The free energy of the system would change e. Nothing; the reaction would stay at equilibrium
Nothing; the reaction would stay at equilibrium
Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description?( a. The metabolism of an organism is isolated from its surroundings b. Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy c. Organisms acquire energy from their surroundings d. Heat produced by the organism is conserved in the organism and not lost to the environment e. all of the above
Organisms acquire energy from their surroundings.
Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? a. The metabolism of an organism is isolated from its surroundings b. Heat produced by the organism is conserved in the organism and not lost to the environment c. Organisms acquire energy from, and lose energy to, their 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.
Organisms acquire energy from, and lose energy to, their surroundings Open systems are those in which energy and materials can be exchanged between the system and its 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? a. The active site must have the wrong configuration to permit succinylcholine binding b. The presence of succinylcholine changes the conditions in the solution, resulting in a denaturation of the enzyme c. Succinylcholine must be an allosteric regulator for this enzyme d. Succinylcholine must be a noncompetitive inhibitor e. Succinylcholine must be a competitive inhibitor with acetylcholine
Succinylcholine must be a competitive inhibitor with acetylcholine Competitive inhibition occurs when a molecule mimics the substrate by competing with it at the active site.
Which of these statements about enzyme inhibitors is true? a. When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback b. A competitive inhibitor binds to the enzyme at a place that is separate from the active site c. The action of competitive inhibitors may be reversible or irreversible d. Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory e. A noncompetitive inhibitor does not change the shape of the active site
The action of competitive inhibitors may be reversible or irreversible Competitive inhibitors that bind covalently to the enzyme would be irreversible, and those that bind weakly would be reversible.
Which of the following statements about the active site of an enzyme is correct? a. The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits b. The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme c. The active site has a fixed structure (shape) d. The structure of the active site is not affected by changes in temperature e. Coenzymes are rarely found in the active site of an enzyme
The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits Only a restricted region of an enzyme molecule (the active site) binds to the substrate. Usually, the active site is formed by only a few of the amino acids, with the rest of the protein molecule providing a framework that reinforces the configuration of the active site.
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
The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water The second law of thermodynamics states that every energy transformation makes the universe more disordered—carbon dioxide and water are more disordered than glucose.
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 lowers the temperature of the active site b. The allosteric inhibitor binds to the substrate and prevents it from binding at the active site 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 binds to the active site, preventing the substrate from binding e. 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 In general, any allosteric regulator functions by changing the structure of the enzyme to change the ability of the active site to bind the substrate.
According to the second law of thermodynamics, which of the following is true? a. The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists b. The entropy of the universe is constantly decreasing c. All reactions produce some heat d. Energy conversions increase the order in the universe e. 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 The second law of thermodynamics demands that total entropy increase with any reaction.
What is meant by the "induced fit" of an enzyme? a. The presence of the substrate in solution induces the enzyme to slightly change its structure b. The shape of the active site is nearly perfect for specifically binding the enzyme's substrate or substrates c. The substrate can be altered so that it is induced to fit into the enzyme's active site d. The enzyme changes its shape slightly as the substrate binds to it e. 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 The enzyme changes slightly to bind to the substrate and catalyze the reaction.
Which of the following statements correctly describe(s) the role or roles 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 always increase the rate of enzyme-catalyzed reactions d. The first and second choices are correct e. The second and third choices are correct
The first and second choices are correct As the heat energy in a system increases, so does the kinetic energy of the reactants. As the kinetic energy of the reactants increases, the reactants are more likely to interact (with each other directly, or with the active site of an enzyme). Subsequently, the reaction rate would increase.
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 c. increasing the substrate concentration d. The first and second listed responses are correct e. The first, second, and third listed responses are correct
The first and second listed responses are correct Either increasing the enzyme concentration or slightly increasing the temperature will increase the rate of product formation.
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
The first and second listed responses are correct Pathways can be displaced from equilibrium either by adding free energy or by removal of the products of the pathway by other reactions.
Which of the following best characterizes the role of ATP in cellular metabolism? a. The charge on the phosphate group of ATP tends to make the molecule very water-soluble b. The ΔG associated with its hydrolysis is positive c. The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate d. The release of free energy during the hydrolysis of ATP heats the surrounding environment e. 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 This is one way a cell can use an exergonic reaction to drive an endergonic reaction.
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 entropy in the products, C and D, is higher than in the reactants, A and B e. 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 is (are) true for anabolic pathways? a. They do not depend on enzymes b. They are usually highly spontaneous chemical reactions c. They consume energy to build up polymers from monomers d. They release energy as they degrade polymers to monomers
They consume energy to build up polymers from monomers
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? a. This is an example of energy coupling b. Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system c. The hydrolysis of ATP is endergonic, and the active transport is exergonic d. Neither ATP hydrolysis nor active transport is spontaneous e. 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 The free energy released from the hydrolysis of ATP is coupled to the energy-requiring active transport of the ion across a membrane.
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. The process of photosynthesis produces energy that the plant uses to grow b. Growth of the crops must occur spontaneously 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
To obey the first law, the crops must represent an open system The first law states that energy cannot be created. The growth of plants stores much energy in the body of the plant. That energy must have been obtained from the plant's environment; thus, the plant must be an open system.
If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to a. add a noncompetitive inhibitor b. add an allosteric inhibitor c. add more substrate d. add more of the enzyme e. heat the solution to 90°C
add more of the enzyme
If an enzyme solution is saturated with substrate, the most effective way to obtain a faster yield of products is to a. add more of the enzyme b. heat the solution to 90°C c. add more substrate d. add an allosteric inhibitor e. add a noncompetitive inhibitor
add more of the enzyme
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. 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 e. 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 This is the best response.
Which of the following is an example of potential rather than kinetic energy? a. a boy mowing grass b. water rushing over Niagara Falls c. a firefly using light flashes to attract a mate d. a food molecule made up of energy-rich macromolecules e. an insect foraging for food
a food molecule made up of energy-rich macromolecules
Which of the following has the most free energy per molecule? a. a cholesterol molecule b. a fatty acid molecule c. a sugar molecule d. an amino acid molecule e. a starch molecule
a starch molecule Starch is a large polymer of sugar and thus contains many covalent bonds.
Which of the following environments or actions affect(s) the rate of an enzyme reaction? a. heating the enzyme b. cooling the enzyme c. substrate concentration d. pH e. all of the above
all of the above
Which of the following is an example of the cellular work accomplished with the free energy derived from the hydrolysis of ATP? a. mechanical work, such as the beating of cilia b. transport work, such as the active transport of an ion into a cell c. chemical work, such as the synthesis of new protein d. all of the above e. none of the above
all of the above
Which of the following statements about enzymes is correct? a. Most enzymes are proteins b. An enzyme is not consumed by the catalytic process c. An enzyme is very specific in terms of which substrate it binds to d. An enzyme lowers the activation energy of a chemical reaction e. all of the above
all of the above
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 __________. a. allosteric activation b. competitive inhibition c. feedback inhibition d. cooperativity e. noncompetitive inhibition
allosteric activation The molecule in this example would be termed an allosteric activator.
The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of ___. a. feedback inhibition b. competitive inhibition c. allosteric regulation d. non-competitive inhibition e. cooperativity
allosteric regulation
How do enzymes lower activation energy? a. by increasing reactivity of products b. by locally concentrating the reactants c. by harnessing heat energy to drive the breakage of bonds between atoms d. The first two responses are correct e. The second and third choices are correct
by locally concentrating the reactants One of the ways enzymes work is to increase the concentrations of reactants at a single place.
Which is the most abundant form of energy in a cell? a. chemical and electrical gradients b. mechanical energy c. heat d. kinetic energy e. chemical energy
chemical energy
Glucose molecules provide energy to power the swimming motion of sperm. In this example, the sperm are changing... a. chemical energy into kinetic energy b. chemical energy into potential energy c. kinetic energy into potential energy d. kinetic energy into chemical energy e. None of the choices are correct
chemical energy into kinetic energy
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? a. denaturization of the enzyme b. allosteric inhibition c. competitive inhibition d. saturation of the enzyme activity e. insufficient cofactors
competitive inhibition
Which curve represents the behavior of an enzyme taken from a bacterium that lives in hot springs at temperatures of 70°C or higher? a. curve 1 b. curve 2 c. curve 3 d. curve 4 e. curve 5
curve 3
Which curve was most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid? a. curve 1 b. curve 2 c. curve 3 d. curve 4 e. curve 5
curve 4
Choose the pair of terms that correctly completes this sentence. Catabolism is to anabolism as _____ is to _____. a. exergonic; endergonic b. work; energy c. exergonic; spontaneous d. entropy; enthalpy e. free energy; entropy
exergonic; endergonic
Bacterial production of the enzymes needed for the synthesis of the amino acid tryptophan declines with increasing levels of tryptophan and increases as tryptophan levels decline. This is an example of ... a. competitive inhibition b. noncompetitive inhibition c. feedback inhibition d. positive feedback e. irreversible inhibition
feedback inhibition
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 above
glucose + fructose » sucrose
Which of the following reactions would be endergonic? a. HCl → H+ + Cl- b. glucose + fructose → sucrose c. ATP → ADP + Pi d. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O e. All of the listed responses are correct
glucose + fructose → sucrose In this case, the product is more complex (lower entropy) than the reactants, and like many anabolic reactions, this one requires an input of energy.
Enzyme activity is affected by pH because ___. a. most substrates don't function well at high or low pH b. high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site c. low pH will denature all enzymes d. changes in pH can cause loss of cofactors from the enzyme e. the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier
high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site
Enzyme activity is affected by pH because __________. a. most substrates do not function well at high or low pH b. low pH will denature all enzymes c. changes in pH can cause loss of cofactors from the enzyme 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. high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site
high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site Each enzyme has an optimal pH at which it is most active, and variations in pH can alter the enzyme's structure, changing activity.
The mechanism of enzyme action is _____ . a. providing energy to speed up the rate of the reaction b. lowering the energy of activation for a reaction c. changing the direction of thermodynamic equilibrium d. changing endergonic into exergonic reactions e. lowering the free energy change of a reaction
lowering the energy of activation for a reaction
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? a. the beating of cilia b. proton movement against a gradient of protons c. facilitated diffusion d. the chemical synthesis of ATP e. chromosome movement on microtubules
proton movement against a gradient of protons Protein pumps that hydrolyze ATP can generate electrochemical gradients.
An exergonic (spontaneous) reaction is a chemical reaction that _____. a. occurs only when an enzyme or other catalyst is present b. cannot occur outside of a living cell c. releases energy when proceeding in the forward direction d. is common in anabolic pathways e. leads to a decrease in the entropy of the universe
releases energy when proceeding in the forward direction
An exergonic (spontaneous) reaction is a chemical reaction that __________. a. occurs only when an enzyme or other catalyst is present b. cannot occur outside of a living cell c. releases energy when proceeding in the forward direction d. is common in anabolic pathways e. leads to a decrease in the entropy of the universe
releases energy when proceeding in the forward direction Exergonic reactions proceed with a net release of free energy, and they occur spontaneously.
In general, the hydrolysis of ATP drives cellular work by __________. a. acting as a catalyst b. releasing heat c. changing to ADP and phosphate d. lowering the activation energy of the reaction e. releasing free energy that can be coupled to other reactions
releasing free energy that can be coupled to other reactions With the help of specific enzymes, the cell can couple the energy of ATP hydrolysis directly to endergonic processes.
Most cells cannot harness heat to perform work because a. heat is not a form of energy b. heat must remain constant during work c. cells do not have much heat; they are relatively cool d. heat can never be used to do work e. temperature is usually uniform throughout a cell
temperature is usually uniform throughout a cell
Which of the following is changed by the presence of an enzyme in a reaction? a. the G value for the products b. the magnitude of ΔG c. the sign of ΔG d. the activation energy e. the G value for the reactants
the activation energy
Which of the following determines the sign of ΔG for a reaction? a. the free energy of the products b. the enzyme catalyzing the reaction's having a high affinity (strength of binding) for the reactants c. the free energy of the reactants d. the enzyme catalyzing the reaction's having a low affinity for the products e. 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 By subtracting the free energy of the reactants from the free energy of the products, the ΔG can be calculated and the difference in these values determines the sign of the difference.
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 conversion of glucose + fructose to make sucrose b. the hydrolysis of ATP c. the active transport of a phosphate ion into the cell d. the contraction of a muscle cell e. the formation of ATP from ADP + Pi
the hydrolysis of ATP With the help of specific enzymes, the cell is able to couple the energy of ATP hydrolysis directly to endergonic processes by transferring a phosphate group from ATP to some other molecule, such as glucose.
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. 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 e. the phosphate groups are polar and are attracted to the water in the cell's interior
the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP Negative charges repel each other. Loss of the terminal phosphate removes some of the repulsion.
A chemical reaction is designated as exergonic rather than endergonic when __________. a. activation energy is required b. the products are less complex than the reactants c. it absorbs more energy d. the potential energy of the products is less than the potential energy of the reactants e. activation energy exceeds net energy release
the potential energy of the products is less than the potential energy of the reactants If a reaction is exergonic, the formation of new bonds releases more energy than was invested in breaking the old bonds.
Some bacteria are metabolically active in hot springs because a. they are able to maintain a cooler internal temperature b. high temperatures make catalysis unnecessary c. their enzymes have high optimal temperatures d. their enzymes are completely insensitive to temperature e. they use molecules other than proteins or RNAs as their main catalysts
their enzymes have high optimal temperatures
Some bacteria are metabolically active in hot springs because a. they are able to maintain a lower internal temperature b. their enzymes are completely insensitive to temperature c. high temperatures make catalysis unnecessary d. they use molecules other than proteins or RNAs as their main catalysts e. 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 __________. a. the enzyme was denatured b. the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme c. the substrate becomes a competitive inhibitor at lower temperature d. there is too little activation energy available e. the hydrogen bonds that define the structure of the enzyme's active site are unstable
there is too little activation energy available The environment usually supplies activation energy in the form of heat. The lower the temperature, the less energy that is available to overcome the activation energy barrier.
Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous? a. ΔS b. TΔS c. ΔH d. ΔG e. All of these values reveal the direction in which a reaction will go
ΔG In any spontaneous process, the free energy of a system decreases. The change in free energy equals the change in total energy minus the change in entropy times the temperature.
If, during a process, the system becomes more ordered, then __________. a. ΔG is positive b. ΔG is negative c. ΔH is negative d. ΔS is negative e. ΔH is positive
ΔS is negative In an endergonic reaction, in which order is increased, the change in entropy, symbolized by ΔS, is negative.
When one molecule is broken down into six component molecules, which of the following will always be true? a. ΔS is negative b. ΔS is positive c. ΔG is positive d. An input of free energy is needed e. ΔH is negative
ΔS is positive The large increase in disorder associated with this reaction means that entropy (ΔS) increases.