Chapter 13 - Microbial Genetics: Regulation of Gene Expression
ANSWERS TO FIGURE MICROINQUIRY QUESTIONS
1. Figure 13.3. Inducer molecules that bind repressor proteins and inhibitor molecules that bind
activator proteins are similar in the fact that both the molecules block binding of its respective
protein to its target DNA thus neither protein can exert its effect on the target DNA.
2. Figure 13.7. When allolactose binds to the lac repressor it acts as an inducer molecule because the
repressor dissociates from the DNA and transcription ensues. (Refer to figure 13.3 for comparison
of corepressors and inducers.
3. Figure 13.10. Phosphorylated OmpR would bind upstream of the ompC promoter in order to
enhance ompC expression and downstream of the ompF promoter to repress ompF expression.
4. Figure 13.11. When bacteria are rapidly synthesizing protein, tryptophan will be in short supply
thus tRNA-trp would also be at low levels so attenuation activity would decrease allowing operon
transcription. Conversely, if tryptophan accumulates because of a deficiency of another amino
acid, attenuation will inhibit the trp operon due to the decrease of protein synthesis.
5. Figure 13.14. Antisense RNA is complementary RNA that base pairs with the target mRNA
blocking ribosome binding. Riboswitches alter the folding pattern of the mRNA leader thus
making the ribosome binding site inaccessible.
6. Figure 13.16. The Aer receptor of the methyl accepting chemotaxis proteins of E. coli does not
need a periplasmic domain because FAD on the cytoplasmic side of the receptor monitors the
presence of oxygen.
7. Figure 13.17. Diauxic growth would be seen with carbon sources that first must be modified
before entering glycolysis such as maltose and galactose.
8. Figure 13.26. Vibrio harveyi produces 3 separate signaling molecules in order to monitor 3
different bacterial populations. HAI-1 allows communication specific to other V. harveyi (and one
closely related species). AI-2 allows detection of a large population of gram positive and gram
negative bacteria and CAI-1 senses members of the genus Vibrio. Three separate signaling
molecules allow V. harveyi to sense 3 different levels of communication.
9. Figure 13.27. The process of sporulation exhibits compartmentation since the cell develops a
forespore and a mother cell within the cytoplasm with the resulting spatial control of gene
expression due to the spatial separation of the sigma factors. Some sigma factors are located in the
mother cell and some in the forespore.