38. A researcher was studying a protein ‘X’ which has been observed to move across
cells when an extracellular electrical stimulus is provided. An artificial peptide ‘P’ was prepared which resembles the structure of connexins and competitively inhibits connexion formation. Which one of the following statements will best explain the fate of protein ‘X’ if the cells are treated with peptide ‘P’ and then electrical stimulus is provided.
(1) X fails to move across cells due to improper formation of tight junctions.
(2) X fails to move across cells due to improper formation of gap junctions.
(3) X moves freely across cells as before.
(4) X fails to move across cells due to improper formation of desmosome

 

The best explanation is:

(2) X fails to move across cells due to improper formation of gap junctions.

Explanation:
Protein ‘X’ moves between cells in response to an extracellular electrical stimulus, implying it passes through intercellular channels. These channels are gap junctions, formed by connexin proteins. The artificial peptide ‘P’ resembles connexins and competitively inhibits connexon formation, thereby disrupting gap junction assembly. Without properly formed gap junctions, the cytoplasmic communication pathways are blocked, and protein ‘X’ cannot move across cells despite electrical stimulation. Tight junctions, desmosomes, or other junctions do not form direct channels for molecule passage between cells, so their disruption would not explain the failure of protein ‘X’ movement.

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Overview of Gap Junction Function

• Gap junctions are channels composed of paired connexons (hemichannels) from adjacent cells.

• Each connexon is a hexamer of connexin proteins.

• These channels allow direct transfer of ions, small metabolites, and signaling molecules between cells.

• Electrical stimuli can influence gating and permeability of gap junctions.

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Effect of Connexin-Mimicking Peptides

• Peptides resembling connexins can competitively block formation of connexons.

• This inhibits gap junction channels, disrupting cell-cell communication pathways.

• Without functional gap junctions, intercellular movement of proteins like ‘X’ is blocked despite extracellular stimuli.

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Conclusion

Disruption of gap junction formation by peptide ‘P’ prevents protein ‘X’ from moving between cells under electrical stimulus, affirming the essential role of connexin-based gap junction channels in rapid intercellular molecular exchange.

Answer: (2) X fails to move across cells due to improper formation of gap junctions.