Question

Differentiate between induction and repression. When and in what systems do the phenomena of
induction and feedback repression operate in a cell system ?

Answer 1

Operon system of gene control can work bases on both induction and repression. This is seen among prokaryotes. Each operon contains regulatory DNA sequences, which act as binding sites for regulatory proteins that promote or inhibit transcription.

1. Induction: Some operons are usually "off," but can be turned "on" by a small molecule. The molecule is called an inducer, and the operon is said to be inducible. For example, the lac operon is an inducible operon that encodes enzymes for metabolism of the sugar lactose. It turns on only when the sugar lactose is present (and other, preferred sugars are absent). The inducer, in this case, is allolactose, a modified form of lactose.
2. Repression: Other operons are usually "on," but can be turned "off" by a small molecule. The molecule is called a corepressor, and the operon is said to be repressible.

For example, the trp operon is a repressible operon that encodes enzymes for synthesis of the amino acid tryptophan. This operon is expressed by default but can be repressed when high levels of the amino acid tryptophan are present. The corepressor, in this case, is tryptophan.