Test Your Knowledge ofTerms and Facts
1. Which of these statements about enzymes is true?
Most proteins are enzymes. Most enzymes are proteins. Enzymes are changed by the reactions they catalyze. The active sites of enzymes have little specificity for substrates. Which of these statements about enzyme-catalyzed reactions is true?
a. The rate of reaction is independent of temperature.
b. The rate of all enzyme-catalyzed reactions is decreased when the pH is lowered from 7 to 2.
c. The rate of reaction is independent of substrate concentration.
d. Under given conditions of substrate concentration, pH, and temperature, the rate of product formation varies directly with enzyme concentration up to a maximum, at which point the rate cannot be increased further.
Which of these statements about lactate dehydrogenase is true?
b. It oxidizes lactic acid.
c. It reduces another molecule (pyruvic acid).
d. All of these are true.
In a metabolic pathway, a. the product of one enzyme becomes the substrate of the next.
b. the substrate of one enzyme becomes the product of the next.
In an inborn error of metabolism, a. a genetic change results in the production of a defective enzyme.
b. intermediates produced prior to the defective step accumulate.
c. alternate pathways are taken by intermediates at branch points that precede the defective step.
d. All of these are true.
Which of these represents an endergonic reaction?
d. CO2 + H2O ^ glucose e. both a and d f. both b and c
Which of these statements about ATP
a. The bond joining ADP and the third phosphate is a high-energy bond.
b. The formation of ATP is coupled to energy-liberating reactions.
c. The conversion of ATP to ADP and Pi provides energy for biosynthesis, cell movement, and
1. Explain the relationship between an enzyme's chemical structure and the function of the enzyme, and describe how both structure and function may be altered in various ways.1
2. Explain how the rate of enzymatic reactions may be regulated by the relative concentrations of substrates and products.
Using the first and second laws of thermodynamics, explain how ATP is formed and how it serves as the universal energy carrier. The coenzymes NAD and FAD can "shuttle" hydrogens from one reaction other cellular processes that require energy.
d. ATP is the "universal energy carrier" of cells.
e. All of these are true.
8. When oxygen is combined with two hydrogens to make water, a. oxygen is reduced.
b. the molecule that donated the hydrogens becomes oxidized.
c. oxygen acts as a reducing agent.
b. decreasing the blood pH.
c. increasing the affinity of reactant molecules for each other.
d. decreasing the activation energy of the reactants.
10. According to the law of mass action, which of these conditions will drive the reaction A + B ^ C to the right?
a. an increase in the concentration of A and B
b. a decrease in the concentration of C
c. an increase in the concentration of d.
enzyme both a and b both b and c to another. How does this process serve to couple oxidation and reduction reactions?
6. Using albinism and phenylketonuria as examples, explain what is meant by inborn errors of metabolism.
7. Why do we need to eat food containing niacin and riboflavin? How do these vitamins function in the body?
1Note: This question is answered in the chapter 4 Study Guide found on the Online Learning Center at www.mhhe.com/fox8.
Enzymes and Energy
Test Your Ability to Analyze and Apply Your Knowledge
Metabolic pathways can be likened to intersecting railroad tracks, with enzymes as the switches. Discuss this analogy.
A student, learning that someone has an elevated blood level of lactate dehydrogenase (LDH), wonders how
the enzyme got into this person's blood and worries about whether it will digest the blood. What explanation can you give to allay the student's fears? Suppose you come across a bottle of enzyme tablets at your local health food store. The clerk tells you this enzyme will help your digestion, but you notice that it is derived from a plant. What concerns might you have regarding the effectiveness of these tablets?
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