As I said before I’m reading for a Ph.D. in bioorganic chemistry, which means that in about 18 months I’ll be a doctor of chemistry.

I’m interested in how living things produce a class of chemicals called terpenes. Although there are about 18,000 different terpenes known they are all built from 2 common building blocks, two chemicals called isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). These two molecules combine to form a chain of 10 carbon atoms which can then either be modified by the organism to leave a 10 carbon molecule (called a monoterpene) or can combine with another molecule of IPP to form larger molecules.

What do terpenes do?

Terpenes are an example of a secondary metabolite – a secondary metabolite being something that the living organism produces in order to be healthy rather than something that is absolutely needed for survival. In your body there is a terpene called ubiquinone (also known as Coenzyme Q) which you need in order to stay healthy by transferring electrons from one place to another. Plants use terpenes for a variety of uses; scientists have found that certain terpenes act as molecules that attract insects so that they can be pollinated (much like a plant perfume), whereas other terpenes are used by plants by discourage insects from feeding on them (antifeedants). A common use for terpenes nowadays is in essential oils that are used in alternative medicine for aromotherapy and in massage oils. Essential oils is the name given to small plant terpenes which are made from one IPP and one DMAPP unit that are fragrant. Examples of this are below
 

Terpenes are also responsible for the beautiful orange/red hues in autumnal leaves. During the time that trees are growing they produce a green substance called chlorophyll that is so intensely coloured it entirely obscures all the other colours in the tree leaves. However, when Autumn causes the growth to stop, the chlorophyll is broken down to leave behind, amongst other things, long terpenes that are brown and orange in colour which are responsible for the Autumnal shades.
 
 

Why do it?

As some plants produce certain terpenes to discourage insects, terpenes are Nature’s insecticides and are all natural and much more environmentally friendly to boot. If we can find out how the DMAPP and IPP building blocks, and thus terpenes, are made then we can use this to encourage plants to produce more terpenes that discourage more pests and thus produce a greater yield of food. Rather than using manmade chemicals we can encourage the plants to fight back themselves. This is just one example of why terpenes are useful and why it is important that we understand how they are made.

Terpenes also go on to form steroids, of which the most famous is cholesterol which has been implicated in heart disease which is the one of the biggest killers in the Western world. Research into this has, and will, save many lives throughout the world.
 
 

THE NEW INTEREST

Recently is has been discovered that there is a new way of making terpenes; historically, all terpenes were though to be made via a molecule called mevalonic acid which is then transformed to IPP and DMAPP and then into terpenes.
 
 

However, it has been shown recently that some plant terpenes and some terpenes produced by bacteria are not made using mevalonic acid, but that the intermediate molecule is something else. That something else is 1-deoxy xylulose (pronounced "zile-yoo-loze") commonly abbreviated to DXU. As yet, we don’t entirely know how living organisms change DXU to the building blocks IPP and DMAPP other than the DXU rearranges by falling apart and reassembling to another molecule, which is commonly abbreviated to MEP.
 
 

The black box really is that – at the moment nobody really knows what happens in there other than MEP goes in and our trusty building blocks IPP and DMAPP come out and go on to form terpenes.

So what about the old way?

The less recently discovered way of making terpenes through mevalonic acid still operates in some plants (typically those which produce medium sized terpenes) and some plants even use both ways. However, it looks as if plants produce their essential oils through the more recently discovered pathway.
 
 

And it’s my remit to explain what’s in the box………