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

Hint: Operon is the cluster of functional protein coding genes present along the DNA. It is a genetic regulatory system that is present in viruses and bacteria. Operon regulates the synthesis of protein as per the need of the cell.

Complete answer:
The Operon system regulates the expression of genes via two systems namely, the induction and the repression. It is often depicted in prokaryotic organisms. Various regulatory DNA sequences are found in each individual operon system which acts as a binding site for attachment of the regulatory proteins thus promoting or inhibiting the transcriptional activities.
Induction: Certain operons remain “off” in most cases but a small molecule can turn them “on” when the regulation is required. This small molecule is known as the inducer molecule and thus the operon system is called the inducible operon.
Repression: In contrast to induction, this operon typically remains “on” but a small molecule known as co-repressor can turn it “off” as and when needed. This type of operon system is repressible operon.
Other differences between induction and repression include:

Induction	Repression
In this process, the operon is turned “on”.	In this process, the operon is turned “off”.
It functions during catabolism.	It functions during anabolism.
It begins the transcriptional and translational activities.	It stops the transcriptional and translational activities.

Phenomenon of induction works in Lac operon which is one of the common examples of inducible operon. It regulates the metabolism of lactose sugar as it encodes the enzymes required for the particular process. When the lactose is present, the operon system is turned “on '' with the help of an inducer. In this particular case, the inducer is allolactose which is a modified form of lactose. Repression occurs in case of Trp operon which is the most common example of this repressible operon. It encodes enzymes for the tryptophan amino acid synthesis. This operon usually remains active but can be repressed in presence of higher concentration of tryptophan amino acid. Tryptophan is the co-repressor in this case. This process is also known as the feedback repression.

Note: Regulatory DNA sequences are found in each operon where regulatory protein can bind to either promote or inhibit further transcriptional activities depending upon the requirement of the cell.