This altered G protein migrates in the plane of the membrane to the catalytic area of the enzyme, which is in an inactive, noncatalytic state. Interaction of the altered G protein with the enzyme causes the enzyme catalytic surface to become activated. The enzyme now will accept substrate molecules and will generate products essential to the cell's biochemistry. Certain receptors for the neurotransmitters norepinephrine, dopamine, and acetylcholine are of this type. The nature of the interaction between a drug molecule and its receptor adds several more degrees of complexity to understanding the chemical mechanisms of drug action.
Nature is asymmetric.
The chemist's rational design of new drug molecules and the pharmacologist's pursuit of understanding of the actions and effects of these molecules in a living system must consider the preceding chemical concepts and parameters. All of them act in concert ultimately to determine whether an organic molecule will produce a pharmacological effect, what that effect will be, where in the body the effect will occur, and how long it will last.