Question

Explain how structural growth of lac operon starts transcription in addition to lactose.

Answer 1

Hint: The Escherichia coli, is a coliform, rod- shaped, facultative anaerobe, gram- negative bacteria. This bacterium is situated in the lower intestine of the warm- blooded organisms. If contaminated food is eaten then some strains of these bacteria could also cause diarrhea.

Complete answer:
In an experiment, when lactose is added into the culture medium of Escherichia coli, the lactose tends to enter into the E.coli. This lactose behaves as a repressor as well as inducer, in the binding. When the repressor binds with the lactose, then it undergoes some conformational changes, as a result the binding site present in the operator undergoes some changes. These changes force the repressor to leave the operator. The operator thus gets free.

The RNA (Ribonucleic acid) polymerase moves over the structural genes and then transcribes the polycistronic mRNA (messenger RNA) that could translate up to three enzymes, namely:
• Beta- galactosidase- this enzyme is produced by gene Z, which converts the lactose into galactose and glucose that are the sources for energy.
• Permease- this enzyme is produced by gene Y, which makes the bacteria permeable to lactose.
• Transacetlyase- this enzyme is produced by gene A, which takes part in some other reactions.
The aforesaid condition of the operon, where the operator is free is known as the switch on condition.

Note: The large molecule of sugar that is formed by two small sugar molecules that is galactose and glucose. For the body to absorb lactose, it must first be splitted into galactose and glucose. These molecules could then be readily absorbed by the cells which forms the lining of the small intestine.