Chapter 8 Mastering

ΔG

– unfavorable reaction – endergonic

-ΔG

– spontaneous reaction – exergonic

ΔH

– products have higher potential energy – unfavorable

-ΔH

– products have lower potential energy – spontaneous

ΔS

– products are more disordered than reactants – spontaneous

-ΔS

– products are more ordered than reactants – unfavorable

When is the overall free energy change ΔG in a reaction most likely to be negative (meaning that the reaction is exergonic)?

A. When products have lower potential energy and higher entropy than reactants
B. When products have higher potential energy and lower entropy than reactants
C. When products have lower potential energy and lower entropy than reactants
D. When products have higher potential energy and higher entropy than reactants

A. When products have lower potential energy and higher entropy than reactants

Electrons tend to have more potential energy when ____.

A. they are in electron shells close to the nucleus
B. they are close to protons
C. they are in electron shells far from the nucleus
D. they are in the nucleus

C. they are in electron shells far from the nucleus

The total energy in a molecule, its enthalpy, is given by the letter ____.

A. H
B. S
C. T
D. G

A. H

Under what conditions could some exothermic (ΔH<0) reactions be nonspontaneous (ΔG>0)?

a. The overall reaction results in an increase in entropy (products have greater entropy than reactants).
b. The products have greater potential energy than the reactants.
c. The products and reactants have equal entropy.
d. The overall reaction reduces entropy (products have less entropy than reactants).

d. The overall reaction reduces entropy (products have less entropy than reactants).

For living organisms, which of the following is an important consequence of the first law of thermodynamics?

a. The entropy of an organism decreases with time as the organism grows in complexity.
b. Organisms grow by converting energy into organic matter.
c. Life does not obey the first law of thermodynamics.
d. The energy content of an organism is constant.
e. The organism ultimately must obtain all of the necessary energy for life from its environment.

e. The organism ultimately must obtain all of the necessary energy for life from its environment.

Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics?

A. Living organisms are able to transform energy into entropy.

B. As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.

C. Life obeys the second law of thermodynamics because the decrease in entropy as the organism grows is exactly balanced by an increase in the entropy of the universe.

D. Living organisms do not follow the laws of thermodynamics.

E. Living organisms do not obey the second law of thermodynamics, which states that entropy must increase with time.

B. As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.

Which of the following statements is a logical consequence of the second law of thermodynamics?

A. Every chemical reaction must increase the total entropy of the universe.
B. If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe.
C. If there is an increase in the energy of a system, there must be a corresponding decrease in the energy of the rest of the universe.
D. Every energy transfer requires activation energy from the environment.
E. Energy can be transferred or transformed, but it cannot be created or destroyed.

A. Every chemical reaction must increase the total entropy of the universe.

The mathematical expression for the change in free energy of a system is ΔG =ΔH – TΔS. Which of the following is (are) correct?

A. ΔH is the change in entropy, the energy available to do work.
B. ΔS is the change in enthalpy, a measure of randomness.
C. ΔG is the change in free energy.
D. T is the temperature in degrees Celsius.

C. ΔG is the change in free energy.

Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

A. α -phosphate (the phosphate closest to ribose)
B/ β-phosphate (the middle phosphate)
C. γ-phosphate (the terminal phosphate)
D. adenine group
E. ribose sugar

C. γ-phosphate (the terminal phosphate)

Which term describes the degree to which an element attracts electrons?

A. Oxidation.
B. Polarity.
C. Electronegativity.
D. Reduction.

C. Electronegativity

Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?

A. Ionic and covalent.
B. Anion and cation.
C. Polar and nonpolar.
D. Proton and electron.

B. Anion and cation.

Which of the following statements is true of the bonds in a water molecule?

A. Oxygen acts as the electron acceptor and is oxidized.
B. There is equal sharing of the electrons between the oxygen atom and the two hydrogen atoms, and the net charge is zero.
C. The electron in each hydrogen atom is completely transferred to the oxygen atom, and each hydrogen atom has a net charge of +1.
D. Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.

D. Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.

Which of the following statements is not true of most cellular redox reactions?

A. The electron acceptor is reduced.
B. A hydrogen atom is transferred to the atom that loses an electron.
C. Changes in potential energy can be released as heat.
D. The reactant that is oxidized loses electrons.

B. A hydrogen atom is transferred to the atom that loses an electron.

Gaseous hydrogen burns in the presence of oxygen to form water:

2H₂ + O₂ → 2H₂O + energy

Which molecule is oxidized and what kind of bond is formed?

A. Hydrogen, polar.
B. Hydrogen, nonpolar.
C. Oxygen, polar.
D. Oxygen, nonpolar.

A. Hydrogen, polar.

How do cells use ATP to raise the energy level of reaction substrates?

A. ATP is hydrolyzed to release its energy.
B. The ADP part of ATP is bound to the substrate.
C. The terminal phosphate of ATP is bound to the substrate.
D. All of the above

C. The terminal phosphate of ATP is bound to the substrate.

Why is ATP a good source of energy for biological reactions?

A. Peroxide links are highly reactive.
B. Links between sugar and phosphate are unstable.
C. Links between adenine and sugar are unstable.
D. Triphosphate chains are unstable.
E. The answer is still unknown

D. Triphosphate chains are unstable.

A reaction is said to be unfavorable if …

A. t will be very slow without a catalyst.
B. The free energy change for the reaction is positive.
C. equilibrium favors the reactants, not the products.
D. Both (a) and (b).
E. Both (b) and (c).

E. Both (b) and (c).

The reaction A → B is unfavorable by itself, but through energy-coupling, cells can use ATP to convert A into B. How is this done?

A. Hydrolysis of ATP releases heat that is used by the unfavorable reaction.
B. ATP acts as a catalyst to speed the unfavorable reaction.
C. The unfavorable reaction is replaced by two favorable reactions.
D. Both (a) and (b).
E. Both (b) and (c).

C. The unfavorable reaction is replaced by two favorable reactions.

How do cells replace the energy-rich ATP that is destroyed in energy-coupled reactions?

A. Chloroplasts use light energy to synthesize ATP.
B. Mitochondria synthesize ATP using energy that’s released by oxidizing sugars and fats.
C. Ribosomes use catalytic RNA to couple ADP with Pi.
D. Both (a) and (b).
E. (a), (b), and (c).

D. Both (a) and (b).

Which statement most accurately explains why ATP hydrolysis is highly exergonic?

A. There is a large increase in potential energy because charge repulsion is reduced.
B. Energy is released when a phosphate group is added.
C. ATP contains the carbohydrate ribose which stores a large amount of chemical energy.
D. There is a large drop in potential energy because charge repulsion is reduced

D. There is a large drop in potential energy because charge repulsion is reduced

Which statement is true for all redox reactions?

A. An atom or molecule loses one or more electrons via reduction.
B. They involve the transfer of electrons.
C. They involve the transfer of hydrogens.
D. An atom or molecule gains one or more electrons via oxidation.

B. They involve the transfer of electrons.

Redox reactions involve the gain or loss of _____.

A. neutrons
B. phosphate
C. electrons
D. protons

C. electrons

When ATP is hydrolyzed into ADP and inorganic phosphate, _____.

A. a redox reaction has occurred
B. there is no change in free energy
C. free energy is released
D. free energy is required

C. free energy is released

Which statement is true of enzymes?

A. Enzymes can be either proteins or RNA molecules.
B. When a cell makes an enzyme, it makes many copies.
C. Their substrate specificity involves matching of shapes.
D. Both (a) and (b).
E. (a), (b), and (c).

E. (a), (b), and (c).

How can "induced fit" influence the specificity of an enzyme?

A. It can not influence the specificity of an enzyme.
B. It moves the reactive portion of the enzyme closer to the substrate.
C. The enzyme’s active site changes shape to fit the correct substrate but not other molecules.
D. Both (b) and (c).
E. None of the above.

D. Both (b) and (c).

Enzymes speed reactions mainly by …

A. protecting the catalysts.
B. lowering EA.
C. raising the kinetic energy of the reactants.
D. providing activation energy.
E. None of the above.

B. lowering EA

Which fact is most important in explaining how enzymes speed reactions?

A. Large molecules collide more energetically than small molecules.
B. High-energy collisions are less common than low-energy collisions.
C. It takes less energy to break a hydrogen bond than a covalent bond.
D. Very low potential energy tends to make molecules unstable.
E. Every reaction step adds to the time required for the overall reaction.

B. High-energy collisions are less common than low-energy collisions.

Can an enzyme make a nonspontaneous reaction occur spontaneously? Why or why not?

A. No, because enzymes do not lower the activation energy of the reaction.
B. No, because enzymes do not affect the overall ΔG of a reaction.
C. Yes, because enzymes lower the activation energy.
D. Yes, because enzymes lower the overall ΔG of a reaction.

B. No, because enzymes do not affect the overall ΔG of a reaction.

How do current models of enzyme function differ from Fischer’s lock-and-key model?

A. Contrary to what Fischer thought, we now know that enzymes are catalysts that can catalyze multiple reactions without being consumed.
B. We now understand that enzyme specificity is due to binding between substrates and amino acids in an enzyme’s active site.
C. There has been no change in our understanding of enzyme function.
D. Rather than enzymes being rigid, we now believe they undergo an induced fit upon substrate binding.

D. Rather than enzymes being rigid, we now believe they undergo an induced fit upon substrate binding.

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?

A. -40 kcal/mol
B. -20 kcal/mol
C. +20 kcal/mol
D. 0 kcal/mol
E. +40 kcal/mol

B. -20 kcal/mol

Which type of control agent never speeds an enzyme’s action?

A. Substrate analog
B. Protein kinase
C. Allosteric effector
D. Regulatory protein
E. None of the above.

A. Substrate analog

Which type of control agent exerts noncompetitive inhibition?

A. Substrate analog
B. Protein kinase
C. Allosteric effector
D/ Both (b) and (c).
E. (a), (b), and (c)

D/ Both (b) and (c).

In cooperativity, …

A. two or more enzymes are needed to bind one control agent.
B. two enzymes share a binding site for a control agent.
C. two enzymes cooperate to produce a control agent.
D. if one substrate is bound, the next binds more easily.
E. two control agents must bind to affect enzyme action.

D. if one substrate is bound, the next binds more easily.

Which statement is characteristic of allosteric effectors?

A. They bind to the active site.
B. Covalent bonds attach them to the enzyme.
C. They may not resemble the enzyme’s substrates.
D. Both (b) and (c).
E. (a), (b), and (c).

C. They may not resemble the enzyme’s substrates.

When a pathway is subject to allosteric feedback inhibition, …

A. the last enzyme in the pathway is allosteric.
B. an accumulation of effectors slows the pathway.
C. the concentration of effectors does not change with time.
D. the effector is made by another pathway.
D. an increase in effector concentration speeds the pathway.

B. an accumulation of effectors slows the pathway.

Which of the following can change the shape of an enzyme?

A. temperature
B. phosphorylation
C. pH
D. all of the above

D. all of the above

An enzyme inhibitor that is roughly the same shape as the substrate and binds at the active site is termed a(n) _____ inhibitor.

A. allosteric
B. competitive
C. noncompetitive
D. catalytic

B. competitive

Which of these is an example of negative feedback?

A. As a blood clot begins to form, the process of its formation gets faster and faster.
B. After you eat, glucagon stimulates an increase in blood sugar levels.
C. After you eat, insulin stimulates the lowering of blood sugar levels.
D. The digestive enzyme pepsinogen is converted to pepsin by the action of hydrochloric acid; pepsin itself can then convert pepsinogen into pepsin.
E. Once labor begins, contractions increase in frequency and intensity.

C. After you eat, insulin stimulates the lowering of blood sugar levels.

The polymerization of amino acids into a protein is an example of _____.

A. an anabolic pathway
B. feedback inhibition
C. a catabolic pathway
D. bioremediation

A. an anabolic pathway

Consider the two-step metabolic pathway: A—(enzyme 1)—>B—(enzyme 2)—>C How would inactivating enzyme 1 affect the concentrations of molecules A, B, and C relative to what they would be if the pathway were fully functional?

A. A and B would decrease; C would increase.
B. A would decrease; B and C would increase.
C. A and B would increase; C would decrease.
D. A would increase; B and C would decrease.

D. A would increase; B and C would decrease.

What do Competitive Inhibition and Allosteric Regulation have in common?

A. Both strategies depend on the concentration of the regulatory molecule.
B. Both are mechanisms where the interaction alters the enzyme’s primary structure.
C. Both are mechanisms that regulate enzymes via covalent modifications.
D. Both strategies are often referred to as a "reversible" modifications.
E. Both are mechanisms that regulate enzymes via noncovalent modifications.

A, D, E

Competitive Inhibition (2)

1. The regulatory molecule binds at the active site 2. The regulatory molecule is similar in size and shape to the enzymes natural substrate

Allosteric Regulation (2)

1. The regulatory molecule binds away from the active site 2. The regulatory molecule changes the shape of the enzyme

Catabolic Reaction

breaks down products to generate a product that a cell might need

Anabolic Reaction

synthesizes a product to be used by the cell

Catabolic reactions will often have

A. a negative ΔG based on a decrease in enthalpy and increase in entropy
B. a positive ΔG based on a decrease in enthalpy and increase in entropy
C. a negative ΔG based on an increase in enthalpy and decrease in entropy
D. a positive ΔG based on an increase in enthalpy and decrease in entropy

A. a negative ΔG based on a decrease in enthalpy and increase in entropy

Anabolic reactions will often have

A. a positive ΔG based on a decrease in enthalpy and increase in entropy
B. a negative ΔG based on a decrease in enthalpy and increase in entropy
C. a negative ΔG based on an increase in enthalpy and decrease in entropy
D. a positive ΔG based on an increase in enthalpy and decrease in entropy

D. a positive ΔG based on an increase in enthalpy and decrease in entropy