Positive and negative feedback Transitional Reasoning Download PDF

Questions

1. 1.

   Researchers investigating cellular communication examine two distinct signal transduction pathways triggered by ligand binding. In Pathway X, the terminal active kinase phosphorylates an upstream receptor, targeting it for rapid degradation. In Pathway Y, the terminal active kinase promotes the secretion of an autocrine ligand that binds to and activates additional surface receptors on the same cell. Based on these mechanisms, which statement correctly classifies the feedback mechanism in each pathway and its physiological consequence?

   • A) Pathway X operates via positive feedback to sustain signaling, whereas Pathway Y operates via negative feedback to prevent ligand depletion.
   • B) Pathway X operates via negative feedback to attenuate signaling and restore homeostasis, whereas Pathway Y operates via positive feedback to amplify the response toward a switch-like outcome.
   • C) Pathway X operates via positive feedback because receptor turnover speeds up kinase recycling, whereas Pathway Y operates via negative feedback by downregulating receptor affinity.
   • D) Both pathways operate via negative feedback because both downstream responses eventually bring receptor activity to a fixed equilibrium.