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Microbiology, 2021

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11.7 • Gene Regulation: Operon Theory 451<br />

cAMP complex to activate transcription of these operons. See Table 11.6 for a summary of the regulation of the<br />

lac operon.<br />

Figure 11.35<br />

When grown in the presence of two substrates, E. coli uses the preferred substrate (in this case glucose) until it is depleted.<br />

Then, enzymes needed for the metabolism of the second substrate are expressed and growth resumes, although at a slower rate.<br />

Figure 11.36<br />

When ATP levels decrease due to depletion of glucose, some remaining ATP is converted to cAMP by adenylyl cyclase. Thus,<br />

increased cAMP levels signal glucose depletion.

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