BIO Chapter 6

Enzyme activity is affected by pH because __________. SHOW HINT high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site changes in pH can cause loss of cofactors from the enzyme most substrates don't function well at high or low pH low pH will denature all enzymes the binding of hydrogen ions to the enzyme absorbs energy and thus, there may not be enough energy to overcome the activation energy barrier

A

The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways? SHOW HINT the hydrolysis of ATP the active transport of a phosphate ion into the cell the contraction of a muscle cell the formation of ATP from ADP + Pi the conversion of glucose + fructose to make sucrose

A

A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10 degrees C and 45 degrees C, with peak activity at 35 degrees C. The most reasonable explanation for the low velocity at 10 degrees C is that ___________. SHOW HINT the hydrogen bonds that define the structure of the enzyme's active site are unstable there is too little activation energy available the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme the substrate becomes a competitive inhibitor at lower temperature the enzyme was denatured

B

According to the second law of thermodynamics, which of the following is true? SHOW HINT 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. The total amount of energy in the universe is constant. All reactions produce some heat. The entropy of the universe is constantly decreasing.

B

An exergonic (spontaneous) reaction is a chemical reaction that __________. SHOW HINT is common in anabolic pathways releases free energy when proceeding in the forward direction occurs only when an enzyme or other catalyst is present cannot occur outside of a living cell leads to a decrease in the entropy of the universe

B

How do enzymes lower activation energy? SHOW HINT 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 above are correct. The second and third choices above are correct.

B

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

B

Which of these statements about enzyme inhibitors is true? SHOW HINT A noncompetitive inhibitor does not change the shape of the active site. The mimic action of competitive inhibitors may be reversible or irreversible. A competitive inhibitor binds to the enzyme at a place that is separate from 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.

B

Molecules A and B contain 110 kcal/mol of free energy and molecules C and D contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded? SHOW HINT The conversion of A and B to C and D is exergonic; the products are less organized than the reactants. 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.

C

The ability to do work or the capacity to cause change is an example of __________. SHOW HINT pinocytosis phagocytosis energy All of the above responses are examples. None of the above responses are correct.

C

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? SHOW HINT High levels of ATP act as an allosteric activator of anabolic pathways. High levels of ATP act as an allosteric activator of catabolic pathways. High levels of ADP act as an allosteric activator of catabolic pathways High levels of ADP act as an allosteric inhibitor of catabolic pathways. High levels of ADP act as an allosteric inhibitor of anabolic pathways.

C

Which of the following functional groups is associated with a release of energy when removed from the carbon skeleton with water that cells can harvest to perform many functions? SHOW HINT carboxyl hydroxyl phosphate amino sulfhydryl

C

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 production of ATP using phosphate from the breakdown of glucose C.the coupling of ATP hydrolysis to the production of a proton gradient across a membrane by a proton pump D.the release of carbon dioxide as glucose is broken down during cellular respiration E.All of the listed responses represent energy transformations.

C

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? SHOW HINT Growth of the crops must occur spontaneously. The process of photosynthesis produces energy that the plant uses to grow. To obey the first law, the crops must represent an open system. The entropy of the universe must decrease to account for the increased entropy associated with plant growth. All of the listed responses are correct.

C

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

D

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? SHOW HINT 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.

D

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously? SHOW HINT The entropy of the organism's environment must also be decreasing. 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. In this situation, the second law of thermodynamics must not apply.

D

Succinylcholine is almost identical to acetylcholine structurally. 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? SHOW HINT Succinylcholine must be a noncompetitive inhibitor. Succinylcholine must be an allosteric regulator for this enzyme. The activation energy barrier for succinylcholine hydrolysis is higher than for acetylcholine hydrolysis. Succinylcholine must be a competitive inhibitor with acetylcholine. The active site must have the wrong configuration to permit succinylcholine binding.

D

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? SHOW HINT In cells, ATP is hydrolyzed to ADP and Pi, but in the test tube it is hydrolyzed to carbon dioxide and water. Cells have the ability to store heat; this cannot happen 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 the cell, the hydrolysis of ATP is coupled to other endergonic reactions. Cells are less efficient at energy metabolism than reactions that are optimized in a test tube.

D

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

D

Which of the following statements about allosteric proteins is/are true? SHOW HINT 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 three listed responses is correct.

D

Which of the following statements correctly describe(s) the role(s) of heat in biological reactions? SHOW HINT 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 increase the rate of enzyme-catalyzed reactions. The first and second choices are correct. The second and third choices are correct.

D

What best characterizes the role of ATP in cellular metabolism? SHOW HINT The release of free energy during the hydrolysis of ATP heats the surrounding environment. It is catabolized to carbon dioxide and water. The charge on the phosphate group of ATP tends to make the molecule very water-soluble. The delta G associated with its hydrolysis is positive. The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

E

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

E

What is meant by the induced fit of an enzyme? SHOW HINT The enzyme changes its shape slightly as the substrate snugly binds to it. The presence of the substrate in solution induces the enzyme to slightly change its structure. The shape of the active site is nearly perfect for specifically binding the enzyme's substrate(s). The substrate can be altered so that it is induced to fit into the enzyme's active site. The enzyme structure is altered so that it can be induced to fit many different types of substrate.

A

Which is the most abundant form of energy in a cell? SHOW HINT chemical energy mechanical energy electrochemical gradients kinetic energy heat

A

Which of the following determines the sign of delta G for a reaction? SHOW HINT the free energy of the reactants and the free energy of the products the free energy of the products the enzyme catalyzing the reaction having a low affinity for the products the free energy of the reactants the enzyme catalyzing the reaction having a high affinity (strength of binding) for the reactants

A

Which of the following statements about enzymes is true? SHOW HINT Enzymes speed up the rate of the reaction without changing the delta G 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. The more heat that is added to a reaction, the faster the enzymes will function. All of the listed responses are correct.

A

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 __________. SHOW HINT 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 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

B

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? SHOW HINT 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. The allosteric inhibitor binds to the substrate and prevents it from binding at the active site. The allosteric inhibitor lowers the temperature of the active site. The allosteric inhibitor binds to the active site, preventing the substrate from binding.

B

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of __________. SHOW HINT cooperativity allosteric regulation competitive inhibition feedback inhibition noncompetitive inhibition

B

What do the sign and magnitude of the delta G of a reaction tell us about the speed of the reaction? SHOW HINT The sign does not matter, but the larger the magnitude of delta G, the faster the reaction. Neither the sign nor the magnitude of delta G have anything to do with the speed of a reaction. The sign determines whether the reaction is spontaneous, and the magnitude determines the speed. The more negative the delta G, the faster the reaction is. The sign does not matter, but the smaller the magnitude of delta G, the faster the reaction.

B

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

B

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

B

Which of the following statements about enzymes is INCORRECT? SHOW HINT Enzymes can be used to accelerate both anabolic and catabolic reactions. 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 which substrate it binds to. Most enzymes are proteins.

B

Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tends to keep these pathways away from equilibrium? SHOW HINT 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.

D

Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? SHOW HINT 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. Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy. Organisms acquire energy from one object to another. All of the listed responses are correct.

D

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

D

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

E

Which of the following has the most free energy per molecule? SHOW HINT an amino acid molecule a fatty acid molecule a cholesterol molecule a sugar molecule a starch molecule

E

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

E

Which of the following statements about the active site of an enzyme is correct? SHOW HINT The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme. 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 may resemble a groove or pocket in the surface of a protein into which the substrate fits.

E

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? SHOW HINT Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system. ATP is acting as a transport protein to facilitate the movement of the ion across the plasma membrane. The hydrolysis of ATP is endergonic, and the active transport is exergonic. Neither ATP hydrolysis nor active transport is spontaneous. This is an example of energy coupling.

E