Genetics: Analysis and Principles 4th Edition by Robert Brooker

Exercise 3

As described in experimental question E2 and also in Chapter 20, the technique of Northern blotting can be used to detect the transcription of RNA. Draw the results you would expect from a Northern blot if bacteria were grown in media that contained lactose (and no glucose) but had the following mutations:
Lane 1. Normal strain
Lane 2. Strain with a mutation that inactivates the lac repressor
Lane 3. Strain with a mutation that prevents allolactose from binding to the lac repressor
Lane 4. Strain with a mutation that inactivates CAP
How would your results differ if these bacterial strains were grown in media that did not contain lactose or glucose
Question E2
Chapter 20 describes a blotting method known as Northern blotting, which can be used to detect RNA transcribed from a particular gene or a particular operon. In this method, a specific RNA is detected by using a short segment of cloned DNA as a probe. The DNA probe is complementary to the RNA that the researcher wishes to detect. After the probe DNA binds to the RNA within a blot of a gel, the RNA is visualized as a dark band. For example, a DNA probe complementary to the mRNA of the lac operon could be used to specifically detect the lac operon mRNA on a gel blot. As shown here, the method of Northern blotting can be used to determine the amount of a particular RNA transcribed under different types of growth conditions. In this Northern blot, bacteria containing a normal lac operon were grown under different types of conditions, and then the mRNA was isolated from the cells and subjected to Northern blotting, using a probe that is complementary to the mRNA of the lac operon.
Based on your understanding of the regulation of the lac operon, explain these results. Which is more effective at shutting down the lac operon, the binding of the lac repressor or the removal of CAP Explain your answer based on the results shown in the Northern blot.