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1. That which carries a message.
2. Having message-carrying properties.
messenger/mes·sen·ger/ (mes´en-jer) an information carrier.
second messenger any of several classes of intracellular signals acting at or situated within the plasma membrane and translating electrical or chemical messages from the environment into cellular responses.
1. Pertaining to ribonucleic acid (RNA) that carries the coded information for protein synthesis from the DNA to the site of protein synthesis, the RIBOSOMES.
2. A HORMONE or other effector capable of acting at a distance from its site of production. A second messenger is a hormone, produced within a cell and operating on internal structures, when another hormone acts on the outer cell membrane.