Question

Which of the following is required as inducer(s) for the expression of Lac operon?
A. Glucose
B. Galactose
C. Lactose
D. Lactose and galactose

Answer 1

Hint: It is the main sugar found in milk. It is a large sugar molecule made up of two small sugar molecules of galactose and glucose.

Complete Answer:
- The lac operon is an operon or unit of genes with one promoter. The genes in the operon encode proteins that make lactose a means of energy use for the bacteria. There are three genes in the lac operon, lacZ, lacY, and lacA. These genes are transcribed under one promoter as single mRNA. Lac operon genes specify proteins to help cells use lactose.
- In lac operon genes LacZ encodes an enzyme that separates lactose into monosaccharides. Likewise, lacY encodes a membrane-built conveyor to help carry lactose into the cell. The lac operon also has many regulatory DNA sequences in addition to the three genes. These are DNA regions to which unique regulatory proteins may attach, which regulate operon transcript.
- Lac operon in E.coli and many other enteric bacteria is an operon necessary for the transportation and the metabolism of lactose. Although glucose is the preferred source of carbon for most bacteria, lac operon can efficiently digest lactose if the action of beta-galactosidase does not allow glucose.
- The lac operon gene regulations were the first well known genetic regulatory system, making it a leading example of prokaryotic gene control. Lactose may be broken by E. coli bacteria. To use lactose, the lac operon genes that are essential enzymes for absorption of lactose and metabolism must be expressed through the bacteria.

Thus, the correct answer is option C. i.e., Lactose.

Note: The lac operon of E. coli carries genes that are involved in the metabolism of lactose. It is only expressed when glucose is absent and lactose is present. In response to glucose and lactose levels, two regulators turn “on” and “off” the operon.