Positive and negative feedback Original Scenario-Based Download PDF

Questions

1. 1.

   In an engineered colony of multicellular biosensors called Astraea, cells communicate to coordinate synchronized bursts of defense enzymes upon detecting trace toxins. When a cell surface receptor binds the toxin, it activates intracellular Kinase-7, which triggers the synthesis and exocytosis of Signal-Q into the extracellular space, prompting neighboring cells and the sender itself to produce and secrete progressively larger amounts of Signal-Q until the entire colony mounts a peak response. Concurrently, to prevent toxic hyperactivation after the external threat subsides, a delayed branch of the cascade gradually accumulates cytosolic Protein-Z, which binds Kinase-7 and shuts down signaling to return the cell to its resting state. Based on these communication pathways, which statement correctly classifies and explains the regulatory feedback mechanisms operating in Astraea?

   • A) Both circuits represent negative feedback because both ultimately preserve cell survival by coordinating defensive action and terminating excessive signaling.
   • B) The Signal-Q circuit operates as negative feedback by driving the system toward an explosive threshold, whereas Protein-Z provides positive feedback by stabilizing the baseline state.
   • C) Kinase-7 activation represents feedforward inhibition, while the accumulation of Protein-Z demonstrates autocrine amplification independent of feedback regulation.
   • D) The Signal-Q pathway operates as positive feedback by amplifying the initial stimulus to drive an all-or-none response, whereas the Protein-Z pathway acts as negative feedback to restore homeostasis.