Gene regulation in prokaryotes/Review

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Question 1: The Arabinose Operon[edit]

Part A[edit]

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

Part B[edit]

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

Part C[edit]

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.

Part D[edit]

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

Part E[edit]

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

Question 2: The Lac Operon[edit]

Part A[edit]

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-ocz+y-

i+o+z+y+/i-ocz+y-

Part B[edit]

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.

External links[edit]