Multiple choice

Which among the following statements regarding the lac operon is incorrect?

  1. The lac repressor is a trimer of identical subunits.

  2. The repressor is an allosteric protein.

  3. Specific control of the lac genes depends on the availability of the substrate lactose to the bacterium.

  4. Transcription of all genes starts with the binding of the enzyme RNA polymerase.

  5. The first control mechanism is the regulatory response to lactose.
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A Correct answer
Explanation

The lac repressor is a tetramer of identical subunits. Each subunit contains a helix-turn-helix (HTH) motif capable of binding to DNA. The operator site where repressor binds is a DNA sequence with inverted repeat symmetry.

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