Question

Mention the differences between the mechanisms of the regulation of gene activity in the lac operon and the try operon in E. coli.

Answer 1

Feature	Lac Operon	Trp Operon
Type of System	Inducible: Normally “OFF” and must be turned on.	Repressible: Normally “ON” and must be turned off.
Metabolic Role	Catabolic: Breaks down lactose for energy.	Anabolic: Synthesises the amino acid tryptophan.
Signal Molecule	Inducer (Allolactose): Its presence switches the operon on.	Co-repressor (Tryptophan): Its presence switches the operon off.
Repressor Status	Active alone: Binds DNA until the inducer releases it.	Inactive alone: Needs the co-repressor to bind DNA.
Number of Genes	3 structural genes: lacZ, lacY, and lacA.	5 structural genes: trpE, trpD, trpC, trpB, and trpA.
Additional Control	Uses Positive Control via the CAP-cAMP complex when glucose is low.	Uses Attenuation to stop transcription early if levels are high.