Question

A mutation occurs in the operator of the Lac Operon. Because of this mutation, the Lac...

A mutation occurs in the operator of the Lac Operon. Because of this mutation, the Lac Repressor is unable to bind to the operator. If a bacterial cell contained this mutation, would the Lac operon be transcribed at a high rate (be on) or off under the following conditions:

Write on or off in the blank next to each of the conditions.

  1. + glucose + lactose ________
  2. + glucose   - lactose ________
  3. - glucose   + lactose ________
  4. - glucose    - lactose ________
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Answer #1

lactose is an inducer of lac operon. Lac repressor binds to the lac operator and inhibit the lac operon in the absence of the inducer, if inducer is present lac repressor cannot bind to the lac operator.

glucose regulate the expression of the lac operator, in the presence of glucose lac operon is inhibited and in the absence of glucose lac operon is expressed at higher levels.

Here the lac operator is mutated such that lac repressor cannot inhibit the lac operon in the absence of lactose, so even in if lactose is absent this lac operon is expressed at very low levels.

In the absence of glucose the lac operon is expressed at higher levels.

  1. + glucose + lactose- Off
  2. + glucose   - lactose- Off
  3. - glucose   + lactose- On
  4. - glucose    - lactose - On
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