molecular messenger signalling molecule A molecular messenger in which the molecule is specifically involved in transmitting information between cells. Such molecules are released from the cell sending the signal, cross over the gap between cells by diffusion, and interact with specific receptors in another cell, triggering a response in that cell by activating a series of enzyme controlled reactions which lead to changes inside the cell. CHEBI:62488 chebi_ontology signal molecule signal molecules signaling molecule signaling molecules signalling molecules