Final answer:
Proteins do not pass through gap junctions because they are too large to fit through the narrow pores that allow the passage of smaller molecules and ions. The correct option is (4) Protein
Step-by-step explanation:
The type of molecule that does not pass through a gap junction is a protein. Gap junctions consist of protein-lined pores between adjacent animal cells, allowing the passage of water and small molecules but not large ones like proteins or nucleic acids.
Ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-), along with small signaling molecules like cyclic AMP (cAMP), inositol phosphate, and cyclic GMP (cGMP), can move through these pores because they are small enough to fit.
By contrast, proteins are generally too large to pass through the narrow pores of gap junctions and typically must be transported using different mechanisms or processes within the cell. The correct option is (4) Protein