Changes in signal transduction and disease Transitional Reasoning Practice

Questions

1. 1.

   Biologists analyzing a malignant tumor cell line discover that genes regulating the cell cycle are continuously transcribed even when extracellular growth factors are entirely absent from the nutrient medium. Further molecular assays reveal that an intracellular relay protein fails to hydrolyze its bound regulatory nucleotide, remaining persistently in its signaling conformation. Which statement best explains how this altered signal transduction mechanism leads to the observed disease phenotype?

   • A) Membrane receptors are rapidly degraded through endocytosis, preventing intracellular second messenger synthesis.
   • B) Intracellular phosphatases dephosphorylate nuclear transcription factors at an accelerated rate, arresting the cell cycle.
   • C) Adenylyl cyclase is competitively inhibited, depleting cellular cyclic AMP reserves and blocking metabolic activity.
   • D) An inability to hydrolyze bound GTP keeps the Ras protein constitutively active, sustaining uncontrolled proliferative signaling.

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