104 Chapter 4
Test Your Knowledge
- Which of these statements about enzymes is true?
a. Most proteins are enzymes.
b. Most enzymes are proteins.
c. Enzymes are changed by the reactions they catalyze.
d. 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?
a. It is a protein.
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?
a. ADP 1 P i → ATP
b. ATP → ADP 1 P i
c. glucose 1 O 2 → CO 2 1 H 2 O
d. CO 2 1 H 2 O → glucose
e. both a and d
f. both b and c- Which of these statements about ATP is true?
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.Review Activities
c. The conversion of ATP to ADP and P i provides energy for
biosynthesis, cell movement, and other cellular processes
that require energy.
d. ATP is the “universal energy carrier” of cells.
e. All of these are true.- When oxygen is combined with 2 hydrogens to make water,
a. oxygen is reduced.
b. the molecule that donated the hydrogens becomes
oxidized.
c. oxygen acts as a reducing agent.
d. both a and b apply.
e. both a and c apply. - Enzymes increase the rate of chemical reactions by
a. increasing the body temperature.
b. decreasing the blood pH.
c. increasing the affinity of reactant molecules for each
other.
d. decreasing the activation energy of the reactants. - According to the law of mass action, which of these
conditions will drive the reaction A 1 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 enzyme
d. both a and b
e. both b and c
Test Your Understanding- 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. - Explain how the rate of enzymatic reactions may be
regulated by the relative concentrations of substrates and
products. - Explain how end-product inhibition represents a form of
negative feedback regulation. - 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 to another. How does this process serve to
couple oxidation and reduction reactions? - Using albinism and phenylketonuria as examples, explain
what is meant by inborn errors of metabolism. - Why do we need to eat food containing niacin and
riboflavin? How do these vitamins function in body
metabolism?
Test Your Analytical Ability- Metabolic pathways can be likened to intersecting railroad
tracks, with enzymes as the switches. Discuss this analogy.