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. signal molecule signalling molecules signaling molecules chebi_ontology CHEBI:62488 signaling molecule signal molecules