Question

Explain the following term in connection with the concept of the lac operon in E.coli:

Cistron

Answer 1

In the context of the lac operon, a cistron is a specific segment of DNA that codes for a single functional polypeptide or protein. Because the lac operon contains three distinct structural genes (lacZ, lacY, and lacA), it is described as being polycistronic. This means that a single long strand of messenger RNA (mRNA) is produced that carries the codes for three different proteins at once.

In E. coli, this polycistronic arrangement is highly efficient; when the operon is “switched on,” the cell produces one mRNA molecule that the ribosomes then translate into three separate enzymes simultaneously. This ensures that the machinery for lactose transport and digestion is always created in a perfectly coordinated fashion.