Prescott’s Microbiology, 9th Edition
Chapter 14 – Regulation of Bacterial Cellular Processes
GUIDELINES FOR ANSWERING THE MICRO INQUIRY QUESTIONS
Figure 14.3 In what way is an inducer molecule that binds a repressor protein similar to an
inhibitor molecule that binds an activator protein?
Both the inducer and the inhibitor small molecules have a specific binding site on their target
protein, and cause the protein to change conformation and lose affinity for DNA, and thus
release from the DNA (compare right panel of A with right panel of d).
Figure 14.7 Is allolactose a corepresor or inducer molecule? Explain your answer.
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 14.3 parts a and b for
comparison of corepressors and inducers.)
Figure 14.10 How does this attenuation respond to rates of protein synthesis in addition to the
intracellular level of tryptophan?
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.
Figure 14.13 How does the inhibition of translation by antisense RNA differ from translational
inhibition by riboswitches?
Antisense RNA comes from a separate gene (a trans effect) and binds to the mRNA of the target
gene, and the ribosome cannot recognize this double-stranded product. A riboswitch is present in
the mRNA of the target gene itself (a cis effect), and blocks translation when a small molecule
ligand is bound. So riboswitch action results from a conformation change in the mRNA, and
does not require the action of another gene.
Figure 14.14 Relative to each promoter, where would you predict phosphorylated OmrP would
bind the ompC and ompF genes?
Since OmpR protein represses ompF gene expression, you would predict it to bind to an operator
sequence downstream or overlapping the promoter, as seen with LacI and the lac operon. This is
because a repressor protein physically blocks binding of RNA polymerase by covering the
transcriptional start site. The OmpR protein activates transcription of the ompC gene, thus you
would expect it to bind upstream of the promoter, as CAP does with the lac operon. Activator
proteins help to recruit RNA polymerase to the promoter.
Figure 14.16 For what other compounds would you also see this kind of diauxic growth?
Other carbohydrates that require modification to enter central metabolism (EMP or ED) would
also typically exhibit diauxic growth.
Figure 14.22 Why doesn’t the Aer receptor need a periplasmic domain?
Aer binds to an intracellular molecule, FAD+ or FADH, to detect the redox status of the cell.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in
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Prescott’s Microbiology, 9th Edition
Figure 14.24 Why does V. harveyi makes three separate signaling molecules?
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. This allows the bacteria to independently
measure the local population levels of three different groups, and thus respond differently to
each.
Figure 14.27 Why would having many GC pairs in the -10 to +1 region of the promoter make it
more difficult to maintain an open complex?
The greater the percentage of GC pairs (as opposed to AT) in a sequence of DNA, the higher the
melting temperature, and so the harder to keep it open with single-stranded segments.
Figure 14.28 Compartmentation – the spatial localization of proteins as a means of regulation –
is usually considered in the context of eukaryotic cells. How is the process of sporulation an
example of compartmentation?
The endospore becomes a membrane-bound compartment inside of the mother cell, thus
allowing the signals and regulation to be different between the two.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in
any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.