Mechanisms of transmembrane signaling are the following EXCEPT:
a) Transmembrane receptors that bind and stimulate a protein tyrosine kinase
b) Gene replacement by the introduction of a therapeutic gene to correct a genetic effect
c) Ligand-gated ion channels that can be induced to open or close by binding a ligand
d) Transmembrane receptor protein that stimulates a GTP-binding signal transducer protein (G-protein) which in turn generates an intracellular second messenger
