Question

6) How is the lac operon regulated if the bacteria is put into an environment where there is excess amount of lactose and glucose at the same time. (10 pts)

Answer 1

This is the case of glucose effect.

When the lactosr and glucose is found excess in the environment, then the glucose substrate is utilised first. After that the lactose is utilised.

Why the Glucose is utilised first?

Because glucose is directly used by the bacteria for producing energy. And lactose requires the more energy for producing energy.

How glucose concentration represses the lactose utilisation?

The glucose leads to convert cAMP into ATP. Hence there is found less cAMP in the bacterial cytoplasm. The cAMP can not bind to the CRP protein. Hence there is not found 90° rotation of CRP sequence. That's why RNA polymerase can not bind to it. Hence lac operon expression is reduced.

When glucose is utilised completely, then cAMP concentration is high. That's why cAMP binds to the CRP protein. Hence CRP activation leads to provide the efficient binding of RNA polymerase to promoter. Hence there is found more expression of lac Structural genes : Z, Y and A. Z encodes beta galactosidase which leadd to break down lactose into glucose and galactose. Y gene allows the entry of lactose into cytoplasm of E. coli. A gene encodes transacetylase. This leads to detoxify the drug.