Question

Which of these Lac operon mero- diploid will be constitutively turned on? Considering the terms has their usual meaning.

(a) I^+ + P + O^+ + Z^+ + Y^+ + A^+ / I^+ + P+ O^+ + Z^+ + Y^+ + A^+

(b) I^+ + P + O^C + Z^+ + Y^+ + A^+ / I^+ + P+ O^+ + Z^+ + Y^+ + A^+

(c) I^s + P + O^+ + Z^+ + Y^+ + A^+ / I^+ + P+ O^+ + Z^+ + Y^+ + A^+

(d) I^+ + P + O^+ + Z^+ + Y^+ + A^+ / I^– + P+ O^+ + Z^+ + Y^+ + A^+

The question was posed to me in semester exam.

My question is from Operons : Lac and Ara in portion Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

The correct answer is (b) I^+ + P + O^C + Z^+ + Y^+ + A^+ / I^+ + P+ O^+ + Z^+ + Y^+ + A^+

The explanation: O^C is an operon that can’t bind to the repressor. Consecutively it is always turned on. I^S produces a repressor which binds tightly to operon and never lets it turn on- This is the case of constitutively turning off.