Which regulatory phenomenon in bacteria is observed when a cell capable of making biosynthetic enzymes does not produce them?

• A. Induction
• B. Repression
• C. Activation
• D. Attenuation

Answer: (B)

Verified step by step guidance

1. Understand the context: The problem asks about a regulatory phenomenon in bacteria where a cell that has the capability to produce biosynthetic enzymes does not actually produce them.
2. Recall the definitions of the options: Induction is when enzyme production is turned on in response to a substrate; Activation involves enhancing gene expression; Attenuation is a mechanism that fine-tunes transcription based on metabolite levels; Repression is when enzyme synthesis is inhibited, usually because the end product is abundant.
3. Identify that biosynthetic enzymes are typically involved in anabolic pathways, where the cell synthesizes essential molecules. When the end product is plentiful, the cell conserves resources by not producing these enzymes.
4. Recognize that this conservation mechanism is called repression, where the presence of the end product (corepressor) binds to a repressor protein, which then inhibits transcription of the biosynthetic enzyme genes.
5. Conclude that the correct regulatory phenomenon described is repression, as it prevents the production of biosynthetic enzymes when they are not needed.