The lac Operon Laboratory

1. The lac Operon Laboratory Purpose: Learning to analyze an example of gene expression Example: lac operon Type of control: negative inducible

2. The Laboratory Worksheet asks: How do mutations affect gene expression of the lac operon?

3. Review: Lac Operon:

4. Mutations and gene expressio of lac operon

5. Oc mutation: a cis acting mutation

6. I- mutation a trans acting mutation

7. Is mutation a trans acting mutation

8. Lab Worksheet: Haploid and Heterozygous Diploid Mutants • Predict if you expect to obtain: • transcription/translation of the lacZ and lacY genes when lactose is absent or present for the E.coli.

9. Try out your ability to reason through the questions.

10. No Lactose - 1 + 2 3 4 5 6 7 8 9

11. The End.

12. Laboratory Exercise

13. Try out your ability to reason through the questions.

14. No Lactose - + I+P+O+Z-Y-/ I-P+O+Z+Y+

15. The next slides are a “key” to the mutations.

16. Experimental tests on the repressor: • I+ cells synthesize full levels of the lac enzymes only in the presence of an inducer • I- mutations NO DNA BINDING ACTIVITY, TRANSCRIPTION OCCURS EVEN IN ABSENCE OF INDUCER! • Is mutation NO LACTOSE BINDING ACTIVITY but has DNA BINDING ACTIVITY. NO TRANSCRIPTION EVEN WITH INDUCER!

17. Experimental mutations to the repressor I s=inducer binding region mutated Inhibits transcription, even with inducer Lactose binding site DNA binding site I - = DNA binding site mutated, prevents binding, allows transcription