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Answers to Text Questions
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Inquiry Questions
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Self Test

1). An atom gains energy when
    a). an electron is lost from it.
    b). it undergoes oxidation.
    c). it undergoes reduction.
    d). it undergoes an oxidation-reduction reaction.

2). Which of the following is concerned with the amount of energy in the universe?
    a). the First Law of Thermodynamics
    b). the Second Law of Thermodynamics.
    c). thermodynamics
    d). entropy

3). In a chemical reaction, if ΔG is negative, it means that
    a). the products contain more free energy than the reactants.
    b). an input of energy is required to break the bonds.
    c). the reaction will proceed spontaneously.
    d). the reaction is endergonic.

4). A catalyst
    a). allows an endergonic reaction to proceed more quickly.
    b). increases the activation energy so a reaction can proceed more quickly.
    c). lowers the amount of energy needed for a reaction to proceed.
    d). is required for an exergonic reaction to occur.

5). Which of the following statements about enzymes is false?
    a). Enzymes are catalysts within cells.
    b). All the cells of an organism contain the same enzymes.
    c). Enzymes bring substances together so they undergo a reaction.
    d). Enzymes lower the activation energy of spontaneous reactions in the cell.

6). A multienzyme complex contains
    a). many copies of just one enzyme.
    b). one enzyme and its substrate.
    c). enzymes that catalyze a series of reactions.
    d). side reactions on a substrate.

7). Which of the following has no effect on the rate of enzyme-catalyzed reactions?
    a). temperature
    b). pH
    c). concentration of substrate
    d). none of these

8). How is ATP used in the cell to produce cellular energy?
    a). ATP provides energy to drive exergonic reactions.
    b). ATP hydrolysis is coupled to endergonic reactions.
    c). A liberated phosphate group attaches to another molecule, which generates energy.
    d). ATP generates energy by the repulsion of the negatively-charged phosphates.

9). Anabolic reactions are reactions that
    a). break chemical bonds.
    b). make chemical bonds.
    c). harvest energy.
    d). occur in a sequence.

10). How is a biochemical pathway regulated?
    a). The product of one reaction becomes the substrate for the next.
    b). The end product replaces the initial substrate in the pathway.
    c). The end product inhibits the first enzyme in the pathway by binding to an allosteric site.
    d). All of these are correct.

Test Your Visual Understanding

1). In which of these two reactions would the change in free energy, ΔG, be positive? Would the product of this reaction have more or less free energy compared to the reactant? Name this type of reaction.
Answer: The change in panel a would result in a positive change in free energy. The product in this reaction would have more free energy than that found in the reactants. This is an endergonic reaction.

2). In which of these two reactions could a catalyst help speed the reaction? How would the catalyst speed the reaction? Name this type of reaction
Answer: The rate of the reaction in panel b could be increased with the aid of a catalyst. The catalyst would reduce the amount of energy that is needed to start the reaction, the activation energy of the reaction. The reactant would bind to the catalyst (an enzyme), which would strain the bonds holding the components of the reactant together allowing them to break more easily. This is an exergonic reaction.

Apply Your Knowledge
1). In a biochemical pathway, three ATP molecules are hydrolyzed. The endergonic reactions in the pathway require a total of 17.3 kcal/mole of energy to drive the reactions of the pathway. What is the overall change in free energy of the biochemical pathway? Is the overall pathway endergonic or exergonic?
Answer: The hydrolysis of a molecule of ATP generates 7.3 kcal/mole and so the hydrolysis of three molecules of ATP would generate:
3 x 7.3 kcal/mole = 21.9 kcal/mole.

The endergonic reactions in the pathway require 17.3 kcal/mole and so the overall change in free energy of the pathway would be:

17.3 kcal/mole - 21.9 kcal/mole = -4.6 kcal/mole

The overall pathway is an exergonic reaction and so it would proceed spontaneously as long as the ATP molecules were available.

2). Oxidation-reduction reactions can involve a wide variety of molecules. Why are those involving hydrogen and oxygen of paramount importance in biological systems?
Answer: Oxygen is highly electronegative meaning that it has a strong affinity for electrons and so it is a great reducing agent in redox reactions. Similarly, hydrogen has a low electronegativity and so willingly gives up electrons in redox reactions. Also, oxygen and hydrogen are very abundant in organic molecules and so they are abundant in biological systems.

3). Almost no sunlight penetrates the deep ocean. However, many fish that live there attract prey and potential mates by producing their own light. Where does that light come from? Does its generation require energy?
Answer: The light, called bioluminescence is created through chemical reactions. When chemical bonds are broken during these chemical reactions, the energy released is emitted as light energy and the organism glows. These chemical reactions are endergonic and require the input of energy–ATP.

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