Prokaryotic Gene Expression Review

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Contents 1 Question 1: The Arabinose Operon 1.1 Part A 1.2 Part B 1.3 Part C 1.4 Part D 1.5 Part E 2 Question 2: The Lac Operon 2.1 Part A 2.2 Part B

[edit] Question 1: The Arabinose Operon

[edit] Part A

Like the products of the lac operon, the products of the ara operon degrade a sugar so it can supply energy for the cell. From this knowledge, would you expect the ara to be repressible or inducible? Explain

[edit] Part B

AraC is required both as an activator and a repressor. Which activity is favored in the presence of arabinose? Explain.

[edit] Part C

When araC mutants were first anaylzed, people concluded that AraC protein acts as an activator, not a repressor. Explain why they came to this conclusion

[edit] Part D

What effect, if any would be the effect of deleting the araO₂ sites where AraC binds?

[edit] Part E

Explain how the presence of glucose will affect expression of the ara operon. Be specific!

[edit] Question 2: The Lac Operon

[edit] Part A

For each of the E.coli diploids that follow, indicate whether the strain is inducible, constitutive or negative for β-galactosidase and permease.

i^-o⁺z^-y⁺/i^-o^cz⁺y^-

i⁺o⁺z⁺y⁺/i^-o^cz⁺y^-

[edit] Part B

Suppose you have isolated a Lac^- mutant and by genetic analysis have found that the cell is z⁺y⁺; you have also found that the mutation, which you call i*, is in the i gene. The diploid i*o⁺z⁺y⁺/i^-o⁺z⁺y⁺ is constructed and found to be Lac^-

^{Is i* dominant or recessive?}

^{The diploid i*o+z+y+/i+ocz+y+ is Lac+. Suggest a property of the mutant repressor that would explain this phenotype. Explain your answer.}

^{Would i*o+z+y+/i+ocz-y+ make β-galactosidase? Explain.|}