Final answer:
A double negative feedback loop occurs when a gene activates itself indirectly through two negative regulatory steps. This allows for precise regulation of gene expression, ensuring genes are activated only when needed.
Step-by-step explanation:
A double negative feedback loop occurs when a gene activates itself indirectly through two negative regulatory steps. In this type of feedback loop, the gene is initially repressed by a repressor protein. However, the presence of a specific molecule or protein removes the repressor, allowing the gene to be transcribed and activated.
For example, in the lac operon system in bacteria, the gene for lactose metabolism is regulated by a double negative feedback loop. The lac repressor protein normally binds to the operator region, preventing the transcription of the lactose metabolism genes. However, when lactose is present, it binds to the repressor protein and changes its conformation, reducing its affinity for the operator. This leads to the activation of the lactose metabolism genes and the production of enzymes necessary for lactose metabolism.
Overall, a double negative feedback loop allows for precise regulation of gene expression, ensuring that genes are activated only when needed.