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Senanu's Bio class

Chapter 18 – Gene Regulation in Prokaryotes

OBJECTIVE: Describe how cells benefit from regulating gene expression

  1. Under what conditions might a bacterium benefit from using transcriptional control of gene expression rather than translational or post-translational control?

  2. Under what conditions might a bacterium benefit from using post-translational control of gene expression?

    OBJECTIVE: Understand the lac, trp, and ara operons and how they serve as a model for how we understand transcriptional regulation.

    Please note: The Freeman textbook does not cover the Arabinose operon. In lab, we manipulate this operon, so please review the linked video to understand how it works.

  3. Under what conditions would the cell ‘want’ to turn ON the trp operon?
  4. What molecule does tryptophan bind to?
  5. What happens to transcription in the presence of tryptophan?
  6. Why is this an example of negative control of gene expression?
  7. Under what conditions would the cell ‘want’ to turn ON the lac operon?
  8. Describe what happens in the absence of lactose.
  9. Describe what happens in the presence of lactose.
  10. Why is this an example of negative control of gene expression?
  11. Why would a cell ‘want’ to shut off the lac operon in the presence of glucose?
  12. The presence of what molecule stimulates the production of cyclic AMP (cAMP)?
  13. What happens in the presence of glucose? What is the final result (in terms of gene regulation)?

  14. In the presence of glucose, cAMP is _____(increased/decreased). This prevents cAMP receptor protein (CRP) from binding to the DNA, causing transcription to stop. Describe the sequence of events that happen when glucose is absent (and lactose is present)

    For each of the operons (lac, ara, trp), understand how modifications to the gene would affect the activity of the cell

  15. How would the cell change (in terms of its ability to metabolize lactose) if there was:

    A. A frameshift mutation in LacI. (remeber that we always expect frameshift mutations to result in non-functional proteins) B. A frameshift mutation in LacZ