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Question
Mention the differences between the mechanisms of the regulation of gene activity in the lac operon and the try operon in E. coli.
Distinguish Between
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Solution
| 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. |
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Chapter 6: Molecular Basis of Inheritance - TEST YOUR PROGRESS [Page 274]
