Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 7
Test Yourself Questions
1. According to the second law of thermodynamics
a. energy cannot be created or destroyed.
b. each energy transfer decreases the disorder of a system.
c. energy is constant in the universe.
d. each energy transfer increases the level of disorder in a system.
e. chemical energy is a form of potential energy.
Answer: d.The second law of thermodynamics states that energy transfer or transformation increases
the level of entropy or disorder of a system.
2. ____________ reactions release free energy.
a. Exergonic
b. Spontaneous
c. Endergonic
d. All of the above
e. Both a and b
Answer: e. Exergonic reactions release free energy and occur spontaneously.
3. Enzymes speed up reactions by
a. providing chemical energy to fuel a reaction.
b. lowering the activation energy necessary to initiate the reaction.
c. causing an endergonic reaction to become an exergonic reaction.
d. substituting for one of the reactants necessary for the reaction.
e. none of the above.
Answer: b. Enzymes function by lowering the activation energy necessary for chemical reactions to
proceed.
4. Which of the following factors will alter the function of enzymes?
a. pH
b. temperature
c. cofactors
d. all of the above
e. b and c only
Answer: d. Temperature, pH, and the presence of cofactors all influence the function of enzymes.
5. In biological systems, ATP functions by
a. providing the energy necessary for an endergonic reaction by coupling it with an exergonic
reaction.
b. acting as an enzyme and lowering the activation energy of certain reactions.
c. adjusting the pH of solutions to maintain optimal conditions for enzyme activity.
d. regulating the speed at which endergonic reactions proceed.
e. interacting with enzymes as a cofactor to stimulate chemical reactions.
Answer: a. ATP hydrolysis (an exergonic reaction) is coupled to an endergonic reaction.
6. During redox reactions, the molecule that donates an electron is said to be
a. reduced.
b. phosphorylated.
c. oxidized.
d. catabolized.
e. methylated.
Answer: c. An atom that donates an electron during a redox reaction is said to be oxidized.
7. Currently scientists are identifying proteins that use ATP as an energy source by
a. determining whether those proteins function in anabolic or catabolic reactions.
b. determining if the protein has a known ATP-binding site.
c. predicting the free energy necessary for the protein to function.
d. determining if the protein has an ATP synthase subunit.
e. all of the above.
Answer: b. Scientists can predict whether a protein uses ATP as an energy source by determining if the
amino acid sequence of the protein includes a known ATP binding site.
8. During glycolysis, ATP is produced by
a. oxidative phosphorylation.
b. substrate-level phosphorylation.
c. redox reactions.
d. all of the above.
e. both a and b
Answer: b. During glycolysis, ATP is produced by substrate-level phosphorylation where an enzyme
attaches a phosphate group directly to ADP. This process differs from oxidative phosphorylation, where
a proton-motive force is generated through a series of redox reactions along the electron transport
chain. This proton-motive force is then utilized by ATP synthase to produce ATP.
9. The energy necessary to produce ATP during oxidative phosphorylation is provided by
a. the H+ concentration gradient produced by the electron transport chain.
b. GTP produced during the citric acid cycle.
c. lactic acid metabolism.
d. the release of CO2 from the mitochondria.
e. all of the above.
Answer: a. During oxidative phosphorylation, the H+ concentration gradient provides energy for ATP
synthesis.
10. Secondary metabolites
a. help deter predation of certain organisms by causing the organism to taste bad.
b. help attract pollinators by producing a pleasant smell.
c. help organisms compete for resources by acting as a poison to competitors.
d. provide protection from DNA damage.
e. all of the above.
Answer: e. All of the choices describe functions of secondary metabolites in living organisms.
Conceptual Questions
1. Distinguish between endergonic and exergonic reactions.
Answer: An exergonic reaction is one that that releases free energy and proceeds spontaneously. An
endergonic reaction has a positive free energy change and does not proceed spontaneously.
2. Define feedback inhibition.
Answer: A form of biochemical regulation in which the product of a metabolic pathway inhibits an
enzyme that acts early in the pathway, thus preventing overaccumulation of the product.
3. The electron transport chain is so named because electrons are transported from one component to
another. Describe the purpose of the electron transport chain.
Answer: The purpose of the electron transport chain is to pump H+ across the inner mitochondrial
membrane to establish an H+ electrochemical gradient. When the H+ ions flow back across the
membrane through ATP synthase, ATP is synthesized.
Experimental Questions
1. The components of the ATP synthase are too small to be visualized by light microscopy. For the
experiment of Figure 7.20, how did the researchers observe the movement of the ATP synthase?
Answer: The researchers attached an actin filament to the ATP synthase. The actin filament was
fluorescently labeled so the researchers could determine if the actin filament moved when viewed under
the fluorescence microscope.
2. In the experiment of Figure 7.20, what observation did the researchers make which indicated that the
ATP synthase is a rotary machine? What was the control of this experiment? What did it indicate?
Answer: When functioning in the hydrolysis of ATP, the actin filament was seen to rotate. The actin
filament was attached to a subunit of the ATP synthase. The rotational movement of the filament was
the result of the rotational movement of the enzyme. In the control experiment, no ATP was added to
stimulate enzyme activity. In the absence of ATP, no movement was observed.
3. Were the observations seen by the researchers in the experiment of Figure 7.20 in the same
direction as expected in the mitochondria during ATP synthesis? Why or why not?
Answer: No, the observation of counterclockwise rotation is the opposite of what would be expected
inside the mitochondria. During the experiment, the enzyme was not functioning in ATP synthesis, but
instead was running backwards and hydrolyzing ATP.
Collaborative Questions
1. Discuss several ways in which metabolic pathways are controlled or regulated.
Answer:
Gene regulation – The gene that encodes an enzyme can be turned off or on.
Cellular regulation – The enzymes involved in metabolic pathways can be controlled by cell-signaling
pathways.
Biochemical regulation – In feedback inhibition, the product of a metabolic pathway inhibits an enzyme
that acts early in the pathway, thus preventing the over accumulation of the product. This occurs when a
molecule binds at an allosteric site, thereby inhibiting the ability of an enzyme to convert reactants to
products. Feedback inhibition is often directed at the enzyme that catalyzes the rate-limiting step in a
metabolic pathway.
2. Discuss the concept of secondary metabolism and give an example.
Answer: Secondary metabolism is the synthesis of chemicals that are not essential for cell structure and
growth and are usually not required for cell survival. These chemicals are typically found in plants,
bacteria, and fungi and play a wide variety of roles such as making an organism toxic to eat or inhibiting
the growth of nearby organisms. One example of secondary metabolites is the flavonoids. These
chemicals are produced by plants and create a variety of smells and colors that either deter or attract
other organisms.