What amplifies the communication from a signal molecule?
use of secondary molecules
check this image
This image shows one set of all the signal transduction occurring in cell. here RTK (Receptor Tyrosine Kinases) which adds a phosphate group to secondary molecules or proteins called secondary messengers upon activation by ligands. these phosphorylated substances then transduce it to the nucleus about signal.
It is not one secondary molecule which is Phosphorylated the receptor keeps on putting Phosphate group on new secondary messengers (it is like a fan till the time ligand is present i.e., electricity is there it will remain switched on) once the ligand is removed the receptor stops putting Phosphate group on new secondary messengers (electricity stops, fan is switched off).
but in the meanwhile a large number of secondary messengers are activated which in turn activates their messengers and this goes on till signal reaches the nucleus.