Chapter 16, Problem 1VCQ

Figure 16.5 In E. coli, the tip operon is on by default, while the lac operon is off. Why do you think that this is the case?

Summary Introduction

To review:

The working of the trp operon and the lac operon in E.coli .

Introduction:

E.coliis a prokaryote with its DNA found clustered in a group of genes that regulate other genes responsible for protein synthesis called the operon. Depending upon the requirement, these operons regulate the gene expression by repression or induction.

Explanation of Solution

E.colineeds amino acids for the synthesis of proteins. One such amino acid required for its survival is the tryptophan. The characteristic trp operon is a group of genes that encode enzymes for the amino acid tryptophan. It is a set of five genes which transcribe into a single amino acid which is further translated to produce five enzymes. The trpoperon is turned on when the tryptophan levels are low leading to the transcription of mRNA, translation of proteins and the synthesis of tryptophan. It is turned off when the levels are high in the environment as tryptophan synthesis is not required due to its abundance. lac operon encodes the genes necessary to acquire and process the sugar lactose from the environment. Lactose is the sugar used by the bacteria only when the glucose concentration is low. Production of enzymes necessary to digest lactose when it is not available is not required. So it is turned on only when lactose is present.

Conclusion

Thus, these conditions of keeping the trp operon on by default and lac operon off is based on the requirement of the enzymes coding tryptophan and lactose.