Question

Explain the following terms in connection with the concept of lac operon in E.coli (a) structural genes b) operon c) cistron (d) polycistron and (e) repressor.

Answer 1

(A) Structural genes are the segments of DNA, which carry codes for the synthesis of proteins. These genes determine the primary structure of a polypeptide chain by having the coding sequence of amino acids in them. For eg, the lac operon of E.coli contains three structural genes, i.e, z, y and a.

(B) An operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter.

(C) Cistron is an alternative term to the gene which is involved in producing a polypeptide chain.

(D) Polycistron is a type of messenger RNA that encode more than one polypeptide.

(E) The repressor is a DNA or RNA binding proteins that inhibit the expression of one or more genes by binding to the operator.