Question

Read the given passage.

Beta-galactosidase (beta-gal) enzyme is used for lactose metabolism . The human intestinal bacteria of three different groups were cultured in a medium containing glucose. At time 1, the bacteria were transferred to media containing lactose as a nutrient source instead of glucose. At time 2, the bacteria were returned to the medium containing glucose. Samples of bacteria were removed at five-minute intervals and tested for the presence of beta-gal. The results are shown by graph.
Which of the following accounts for the inability of group 3 to produce beta-gal?

I. Error in DNA replication

II. Error in RNA transcription

III. Error in protein translation

• A. I only
• B. III only
• C. I and II only
• D. II and III only
• E. I, II, and III

Answer 1

The correct option is E I, II, and III

Lac-operon is inducible operon and is transcribed only when lactose is available. If the bacteria is not producing -gal, it shows inability to synthesize the protein even when lactose is present in the medium. Synthesis of -gal enzyme required DNA replication followed by transcription of -gal mRNA and then its translation in to gal enzyme. Error in any of these process can prevent synthesis of the enzyme. This makes option E correct answer.