Difference Between Induction and Repression

Introduction imageThe difference between induction and repression of operon is mainly due to the following factors:
Regulation: The operon system in prokaryotes regulate the expression of enzymes necessary to turn on or off the metabolic pathway. The regulatory gene of inducible operon forms an active repressor protein, whose binding affinity towards the operator region is mediated by the inducer. An inducer functions as an anti-repressor, whose presence induces the expression of enzymes by suppressing the activity of the repressor protein.

Oppositely, the regulatory gene of repressible operon synthesizes apo-repressor protein, whose activity is controlled by the corepressor. The corepressor functions as an effector molecule, whose presence activates the apo-repressor protein that in turn represses the enzyme synthesis.

Role: The induction system significantly turns on the operon system via association of inducer and repressor protein, whereas the repression system switches off the operon system via a complex formed by the combination of corepressor and apo-repressor protein.

Content: Induction Vs Repression

  1. Comparison Chart
  2. Definition
  3. Key Differences
  4. Conclusion

Comparison Chart

PropertiesInductionRepression
MeaningThe meaning of induction states that it will induce the gene expression via an inducerThe meaning of repression states that it will repress the gene expression via a corepressor
RegulationThe operon system regulates the synthesis of enzymes that are stimulated by the addition of inducerThe operon system represses the enzyme synthesis, which is facilitated by the existing end-product or corepressor molecules
Key elementInducer or anti-repressorCorepressor or effector molecule
MechanismInducer inactivates the repressor protein, and prevents the attachment of a repressor to the operator regionCorepressor activates the apo-repressor protein (inactive), which allows the attachment of an active repressor to the operator region
Effect on the control systemMediates movement of the RNA polymerase along the control system, i.e. promoter and operator regionBlocks the movement of RNA polymerase along the promoter and operator region
Effect on structural genesIt initiates the expression of structural genesIt inhibits the expression of structural genes
Overall impactAn induction system activates or turns on the whole operon system through an adequate supply of the inducer metabolitesA repression system terminates or switches off the entire operon system by an adequate level of corepressor molecules
Operon systemThe genetic system regulated by the presence or absence of an inducer is called inducible operon The genetic system regulated by the presence or absence of a corepressor is called repressible operon
EnzymeEnzymes synthesis stimulated by the addition of inducer metabolites are termed as inducible enzymesEnzymes synthesis inhibited by the addition of corepressor molecules are termed as repressible enzymes
ExampleLactose operon Tryptophan operon
Metabolic pathwayIt operates a catabolic synthesisIt operates an anabolic synthesis

Definition of Induction

The induction of operon facilitates the synthesis of enzymes that are stimulated by the supply of inducer or substrate to the prokaryotic cells. For instance, β-galactosidase is an enzyme that causes hydrolysis of lactose (substrate) into simple products, i.e. glucose and galactose via an  inducer (Allolactose).

Inducible system

Here, the addition of inducer (Allolactose) initiates the enzyme synthesis necessary for the hydrolysis of lactose by suppressing the active repressor protein. If the supply of lactose to E. coli cells is ceased, then the production of enzyme β galactosidase will also halt, and vice versa. Therefore, lactose operon is the best example to study the induction system, where the addition of lactose increases the synthesis of β galactosidase to the rate of 10,000 times.

Regulation of inducible operon

When the enzyme synthesis gets increased by the addition of inducer, then such enzymes are known as inducible enzymes. A genetic system that regulates the enzyme synthesis via an inducer is termed an inducible operon. Thus, inducible operon conducts the catabolic pathway like catalysis of oligosaccharide into simple sugar.

Definition of Repression

The repression of operon facilitates the cessation of the enzyme synthesis at the appropriate level of particular amino acid. For instance, tryptophan is an amino acid whose supply can repress the production of tryptophan synthesizing enzymes.

repressible system

Here, tryptophan amino acid functions as a corepressor molecule that associates with the apo-repressor protein, and transform into an active form. The active repressor then terminates the tryptophan synthesizing enzymes. If there is no supply of tryptophan from outside, the E.coli cells can express the genes for trp production. On contrary, the trp synthesizing enzymes fall down when there is high trp level.

Regulation of repressible operon

When the synthesis of the enzyme is decreased by the high concentration of corepressor, then such enzymes are known as repressible enzymes. A genetic system that regulates the enzyme synthesis via a corepressor is termed as a repressible system. Thus, repressible operon in E.coli conducts the anabolic pathway like the production of amino acids.

Key Differences Between Induction and Repression

  1. The meaning of induction and repression states that the former will induce and the latter will repress the gene expression in the presence of inducer and corepressor, respectively.
  2. The induction system regulates the synthesis of enzymes initiated by the supply of an inducer. Contrarily, the repressor system inhibits the enzyme synthesis that is facilitated by the existing end-product or corepressor molecules.
  3. Inducer or anti-repressor metabolite and the corepressor or effector molecule are the key elements of the induction and repression system.
  4. Inducer deactivates a repressor protein and prevents the attachment of a repressor to the operator region. In contrast, a corepressor activates an apo-repressor protein (inactive) and facilitates the joining of an active repressor to the operator region.
  5. An induction system activates or turns on the whole operon system by the adequate supply of the inducer metabolites. In contrast, a repression system terminates or switches off the whole operon system by the adequate level of pre-existing corepressor molecules.
  6. Lactose operon is the best example of an inducible operon, in which the addition of an inducer (Allolactose) stimulates the synthesis of β-galactosidase (inducible enzyme) necessary for the breakdown of lactose into glucose and galactose. Oppositely, tryptophan operon is the best example of a repressible operon that regulates the tryptophan synthesizing enzymes to construct tryptophan, whose synthesis is repressed by the addition of corepressor.
  7. An inducible operon conducts a catabolic synthesis, where a complex molecule breaks down into simpler form. In contrast, a repressible operon conducts an anabolic synthesis of a product through the combination of simple or smaller units.

Conclusion

Therefore, the induction and repression of the operon are the two mechanisms that regulate the synthesis of different enzymes, and decides when to turn on or turn off the biosynthetic pathway.

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