Chapter 8 Practice Test Questions

Which of the following environments or actions would NOT affect the rate of an enzyme reaction? substrate concentration pH cooling the enzyme heating the enzyme *None of the listed responses is correct.

*None of the listed responses is correct.

Which of the following statements correctly describe(s) the role or roles of heat in biological reactions? 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.

- 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.

Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend(s) to keep these pathways away from equilibrium? 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 continuous removal of the products of a pathway to be used in other reactions -an input of free energy from outside the pathway

Which of the following statements about allosteric proteins is/are true? They exist in active and inactive conformations. They are sensitive to environmental conditions. They are acted on by inhibitors. 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? Enzymes can be used to accelerate both anabolic and catabolic reactions. An enzyme lowers the activation energy of a chemical reaction. An enzyme is consumed during the reaction it catalyzes. Most enzymes are proteins. 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 correctly states the relationship between anabolic and catabolic pathways? Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules. Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. The flow of energy between catabolic and anabolic pathways is reversible.

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? 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. Energy can be freely transformed among different forms as long as the total energy is conserved. Photosynthetic organisms produce energy in sugars from sunlight. Living organisms must increase the entropy of their surroundings.

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? In this situation, the second law of thermodynamics must not apply. Heat is being used by the organism as a source of energy. The first law of thermodynamics is being violated. Energy input into the organism must be occurring to drive the decrease in entropy. The entropy of the organism's environment must also be decreasing.

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

Which of the following statements about enzyme function is correct? Enzymes can greatly speed up reactions, but they cannot change the activation energy because they cannot change the net energy output. Enzymes can change the equilibrium point of reactions, but they cannot speed up reactions 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 lower the activation energy of reactions, but they cannot change the equilibrium point 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? Enzymes react with their substrate (form chemical bonds), forming an enzyme-substrate complex, which irreversibly alters the enzyme. Enzymes speed up the rate of the reaction without changing the DG for the reaction. Enzymes increase the rate of a reaction by raising the activation energy for reactions. The more heat that is added to a reaction, the faster the enzymes will function. All of the listed responses are correct

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

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? Cells are less efficient at energy metabolism than reactions that are optimized in a test tube. The amount of heat released by a reaction has nothing to do with the free energy change of the reaction. 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. Cells have the ability to store heat; this cannot happen 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? The sign determines whether the reaction is spontaneous, and the magnitude determines the speed. The sign does not matter, but the smaller the magnitude of ΔG, the faster the reaction. The sign does not matter, but the larger the magnitude of ΔG, the faster the reaction. 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.

Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction.

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

Succinylcholine must be a competitive inhibitor with acetylcholine.

Which of these statements about enzyme inhibitors is true? 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. A noncompetitive inhibitor does not change the shape of the active site. Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory. When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.

The action of competitive inhibitors may be reversible or irreversible.

Which of the following statements about the active site of an enzyme is correct? The active site has a fixed structure (shape). 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 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?

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? The entropy of the universe is constantly decreasing. The total amount of energy in the universe is constant. All reactions produce some heat. The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists. Energy conversions increase the order in the universe.

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? The enzyme structure is altered so that it can be induced to fit many different types of substrate. The presence of the substrate in solution induces the enzyme to slightly change its structure. The substrate can be altered so that it is induced to fit into the enzyme's active site. The enzyme changes its shape slightly as the substrate binds to it. 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.

Which of the following best characterizes the role of ATP in cellular metabolism? The charge on the phosphate group of ATP tends to make the molecule very water-soluble. The release of free energy during the hydrolysis of ATP heats the surrounding environment. The DG associated with its hydrolysis is positive. 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 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? The conversion of A and B to C and D is spontaneous. 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. 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 reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants.

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? 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 _______ 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 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

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 __________.

allosteric activation

How do enzymes lower activation energy? 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

Which of the following reaction would be endergonic? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O HCl → H+ + Cl- glucose + fructose → sucrose ATP → ADP + Pi All of the listed responses are correct.

glucose + fructose → sucrose

Enzyme activity is affected by pH because __________. the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier changes in pH can cause loss of cofactors from the enzyme most substrates do not function well at high or low pH low pH will denature all enzymes 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

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? proton movement against a gradient of protons facilitated diffusion the beating of cilia the chemical synthesis of ATP chromosome movement on microtubules

proton movement against a gradient of protons

An exergonic (spontaneous) reaction is a chemical reaction that _____. is common in anabolic pathways cannot occur outside of a living cell releases energy when proceeding in the forward direction 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

In general, the hydrolysis of ATP drives cellular work by __________. lowering the activation energy of the reaction acting as a catalyst releasing free energy that can be coupled to other reactions releasing heat changing to ADP and phosphate

releasing free energy that can be coupled to other reactions

Which of the following is changed by the presence of an enzyme in a reaction? the activation energy the magnitude of ΔG the sign of ΔG the G value for the products the G value for the reactants

the activation energy

Which of the following determines the sign of ΔG for a reaction? he free energy of the reactants the free energy of the products the enzyme catalyzing the reaction's having a high affinity (strength of binding) for the reactants the enzyme catalyzing the reaction's having a low affinity for 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? the formation of ATP from ADP + Pi the conversion of glucose + fructose to make sucrose the active transport of a phosphate ion into the cell the hydrolysis of ATP the contraction of a muscle 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 __________. the bonds between the phosphate groups are unusually strong and breaking them releases free energy 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 the valence electrons in the phosphorus atom have less energy on average than those of other atoms 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

A chemical reaction is designated as exergonic rather than endergonic when __________. the potential energy of the products is less than the potential energy of the reactants activation energy is required activation energy exceeds net energy release it absorbs more energy the products are less complex than the reactants

the potential energy of the products is less than the potential energy of the reactants

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 __________. there is too little activation energy available the enzyme was denatured the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme 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

Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous?

ΔG

If, during process, the system becomes more ordered, then _____

ΔS is negative

When one molecule is broken down into six component molecules, which of the following will always be true?

ΔS is positive