What is the operational state of negative repressible operons?

Negative repressible operons are typically in an "on" state under normal conditions, where genes can be expressed and the corresponding enzymes or proteins are synthesized. Their primary regulatory mechanism involves a repressor protein that can bind to the operator region of the operon. When a specific metabolite or product accumulates, it can bind to the repressor, causing a conformational change that allows it to bind to the operator, which in turn prevents transcription of the operon.

Thus, when the product is present, the operon is repressed, leading to decreased expression of the genes involved. Therefore, the operational state of these operons is characterized by being "on" since they are actively being transcribed until the repressive mechanism is activated by the binding of the repressor. This dynamic regulation allows the cell to conserve resources by stopping the expression of genes involved in pathways when their products are readily available.

In summary, the choice indicating that negative repressible operons are "on and can be repressed" accurately represents their functional state, as they are actively transcribing genes until a specific metabolite induces repression.