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CHAPTER 16
Concept check questions (in figure legends)
FIGURE 16.1
Concept check: What is an advantage of gene regulation?
Answer: Gene regulation is more efficient. A cell does not was energy making RNAs and
proteins it does not need.
FIGURE 16.2
Concept check: Which of these are genetic regulatory proteins and which are small
effector molecules?
Answer: Activators and repressors are regulatory proteins. Inducers, corepressors, and
inhibitors are small effector molecules.
FIGURE 16.3
Concept check: Which genes are under the control of the lac promoter?
Answer: The lacZ, lacY, and lacA genes are under the control of the lac promoter.
FIGURE 16.5
Concept check: Under what conditions is the lac repressor bound to the lac operon?
Answer: The lac repressor is bound to the lac operon when it is not exposed to lactose—
when allolactose is not bound to the repressor.
FIGURE 16.8
Concept check: Why is it beneficial to the bacterium to regulate the lac operon with both
a repressor protein and an activator protein?
Answer: The repressor protein allows the cell to avoid turning on the operon in the
absence of lactose. The activator protein allows the cell to choose between glucose and
lactose.
FIGURE 16.9
Concept check: Which data provide the strongest evidence that O1 is not the only
operator site?
Answer: The data in which O2 and O3 are deleted indicate that O1, by itself, is not very
strong in repressing the lac operon.
FIGURE 16.11
Concept check: How does tryptophan affect the function of the trp repressor?
Answer: Tryptophan acts as a corepressor that causes the trp repressor to bind to the trp
operon and repress transcription.
FIGURE 16.12
Concept check: What type of bonding interactions cause the stem-loops to form?
Answer: Hydrogen bonding between complementary sequences causes the stem-loops to
form.
FIGURE 16.13
Concept check: Explain how the presence of tryptophan favors the formation of the 3-4
stem-loop.
Answer: The presence of tryptophan causes the trpL gene to be translated to its stop
codon. This blocks both regions 1 and 2, which allows a 3-4 stem-loop to form. The 3-4
stem-loop causes transcriptional termination.
FIGURE 16.14
Concept check: How does micF antisense RNA affect the translation of ompF mRNA?
Answer: The micF antisense RNA binds to the ompF mRNA and inhibits its translation.
FIGURE 16.15
Concept check: Why is feedback inhibition an advantage to the bacterium?
Answer: Feedback inhibition prevents a bacterium from over producing the product of a
metabolic pathway.
FIGURE 16.16
Concept check: Which RNA conformation favors transcription—the form with the
antiterminator stem-loop or the form with the terminator stem-loop?
Answer: The RNA conformation with an antiterminator stem-loop favors transcription.
FIGURE 16.17
Concept check: Which RNA conformation favors translation—the form with the ShineDalgarno antisequestor or the form in which the Shine-Dalgarno sequence is in a stemloop structure?
Answer: The RNA conformation with the Shine-Dalgarno antisequestor favors
translation.