Question

4. Select the single true statement about Lac repressor and explain why others are wrong (1 pt).

1. Lac repressor only associates with DNA in the presence of Lactose
2. Lac repressor binds to DNA as monomers
3. Lac repressor binding bends the DNA to prevent transcription
4. Lac repressor contacts DNA using multiple beta strands
5. Lac repressor association with DNA decreases Lactose concentration

please say why all others are wrong too, thank you!

Answer 1

lac repressor binds to the lac operator as a dimer- so B is wrong.

lac repressor is inhibited by lactose so if lactose is present lac repressor cannot bind to the DNA- so A is wrong.

lac repressor binds to the lac operator and inhibits the expression of lac operon, the genes in the lac operon is functions to breakdown lactose to glucose and galactose, so if the lac repressor is bound to the lac operator, the lactose concentration does not decrease so statement E is wrong.

DNA binding domain of the lac repressor has helix-turn-helix that is DNA binding region consists of alpha-helices so D is wrong.

when the lac repressor binds to the DNA, DNA bends by about 60 Ao radius of curvature.

so the answer is c) Lac repressor binding bends the DNA to prevent transcription.