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MBBS QUESTION #10374
Question 1
Peptide hormones (e.g., insulin, glucagon, growth hormone), being water-soluble and unable to cross the lipid plasma membrane, characteristically act via:
  • Direct diffusion into the cell to bind intracellular nuclear receptors
  • Binding cell-surface receptors, frequently triggering second-messenger cascades (e.g., cAMP, IP3/DAG) or intrinsic/associated tyrosine kinase activity✔️
  • Binding exclusively to mitochondrial receptors within the target cell
  • Acting entirely without any receptor-mediated mechanism
Correct Answer Explanation
Because peptide hormones cannot cross the plasma membrane, they bind specific cell-surface receptors, initiating rapid intracellular signaling cascades (second messengers or receptor kinase activity) that alter existing protein/enzyme activity, generally producing a faster-onset response than steroid hormone signaling.