Essential Oils

Molecular  Target: Cell Membrane 

The cell membrane seperates the reaction space of the cell from the surrounding environment. Without cell membranes , there would not have been any evolution of higher life forms. Nerve and tissue cells are surrounded by a double lipid layer membrane 5 nanometers wide.

Most water-soluble molecules cannot penetrate the membrane, only nonpolar or very small molecules like O2, CO2, or water can permeate the membrane uninhibited. The necessary exchange of amino acids, sugars, and signaling are performed by proteins integrated into the membrane.

One of the most oustanding qualities of nerve and sensory cells is their ability to generate and conduct electric signals.This is the result of the membranes' ability to seperate charges and the ability of specific membrane proteins (ion pumps) to affect controlled change in conductivity.

Many of the effects of essential oil molecules are a consequence of their ability to modify this electric signaling.

They do so by modifying membrane function in two ways;

1. They can either insert themselves into the lipid membrane, creating hydrophobic interactions with the lipophilic chains of the phospholipids or cholesterol. In this fashion the terpens in essential oils change membrane fluidity or permeability and ultimately structure and functionality.

2.Essential oil molecules can change membrane function by attaching to the lipophilic areas of the membrane proteins, that is, receptor proteins.

As terpenoids form hydrophobic interactions with those segments of the receptor, which are themselves lodged in the membrane, they modify its conformation (its three dimensional structure) and hence functionality.

A well-known example for this is the interference of terpenoids with the ion channels in nerve cell membranes, modifying neuromuscular activity to relieve spasms at smooth intestinal muscle cells. Interference of high concentrsations of terpenoids with membranes also mediates their narcotic anesthetic effects. 

Summation of Physiological Activity of Secondary Plant Metabolites

To recap, secondary plant metabolites utilize a variety of strategies to connect with molecular targets:

Selective interaction with specific molecular targets such as neuro-or hormone receptors.

Disturbane of the three-dimensional structure proteins

Covalent bonding to DNA and RNA, modifying gene expression

Changing membrane permeability and the function of membrane proteins.

Only the first mechanism-the interaction of a secondary metabolite with an active site of a protein- is selective and specific. Such interactions are very powerful, but their disadvantage is that they are generally restricted to a small number of enemies who have the specific target.

Molecules that disturb the conformation of proteins, the structure of DNA and RNA, or the fluidity of membranes are obviously nonselective. Such molecules interact with many different targets. Although nonspecific, these interactions are very effective, because they disturb molecular targets in whatever enemy attacks the plant. 

Reference: The Healing Intelligence of Essential Oils: Kurt Schnaub elt