ABSTRACT
For example, a hormone, drug, neurotransmitter, or another “signal” binds to a receptor molecule on the surface of the cell’s exterior membrane. That receptor then activates the Gprotein. This causes an effector inside the cell to produce a second “signal” chemical inside the cell, which causes the cell (nucleus) to react to the original external chemical signal. G-proteins are called thus because they become GTP and GDP forms alternately as part of their reaction cycle (i.e., in “passing the signal”).
