Part 6: Phytochemistry—Terpenes and Terpenoids

There are thousands of types of mono-, sesqui-, di-, tri-, tetra- terpene compounds (which differ by their molecular weight), many of which have been widely studied. These compounds are found throughout nature and are found in most plants. Many of the monoterpenes are known for their potent aromas, high volatility which can attract insects to the plant flowers for pollination. The essential oils isolated from rose, peppermint, lemon and lavender contain numerous oxygenated monoterpenes, aliphatic and aromatic compounds that give these oils their uniquely pleasant fragrance. Other non-aromatic terpenes and higher molecular weight terpenes can act as protective compounds, providing the plant with a bitter taste, pungent aroma, or sticky texture to repel potentially harmful predators. Another protective characteristic of terpenes is their hydrophobicity (water-repelling character), which allows them to easily cross the lipid membranes of invading cells. Upon traversing a cellular membrane, these compounds can increase the fluidity of the membrane so the cell is unable to maintain a balanced environment. Because cells rely heavily on the equilibrium of their internal environment, this can cause apoptosis(cell death). Although terpenes are often not life threatening for large organisms (such as animals and humans) they can be effective against many environmental threats. 

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