Question

1. (1 pt) If a gene is repressible and under positive control,
A. Is the regulatory protein an activator or repressor?
B. Explain how an effector molecule, which binds to the regulatory protein, alters the regulatory protein’s ability to regulate expression of the gene.

2. (1 pt) Cis and trans are two terms used to describe mutations.
A. Explain the molecular difference between these terms.
B. indicate which type of mutation (cis or trans) is dominant to wild-type and which is recessive in partial diploids.

3. (1 pt) Concerning the functional form of the lac repressor protein,
A. Why aspect of its functional form suggested that the lac operon may contain more than one operator site? B. How do we know that all three lac operators are required for full repression?

6. (2 pt) E. coli cells are grown in a medium containing lactose but no glucose. Indicate wheter each of the following changes or conditions would increase, decrease, or not change expression of the operon:

A. relocate the lac operator so that it is on the 3’ end of the operon (at the end of the gene)
B. mutant and therefore inactivate the binding site for the CAP protein

C. mutate and therefore inactivate the -10 and -35 sites so that they match the consensus sequence for these sites D. Addition of a large amount of glucose

E. mutation that prevents the lac repressor from binding the operator
F. mutation that completely inactivates the lacY gene

Answer 1

1. A. The gene is acting as a repressor.

B. Binding of an effector molecule may activate or repress the activity. In this case, it may activate the expression of a gene.