Metabolic chemistry  




It is no accident that carbon is the basis of living organisms. The carbon atom is the smallest atom which has a valency of four (ie the greatest interconnectivity), and so molecules based on carbon can form a much wider range of shapes than based on any other element. Biochemistry is complex because of the wide range of shapes that is possible, leading to molecules with very different properties.

The simplest carbon molecule is methane (CH4). If we take two molecules of methane, and remove a hydrogen atom from each, we can connect the two carbon atoms together to form a new molecule called ethane (C2H6) [picture]. Clearly we could continue to do this, taking the hydrogen atom off the end and adding a CH3 group. The names follow the latin numbers, so the molecule with a chain of six carbon atoms (C6H14) is hexane, the molecule with a chain of eight carbon atoms (C8H18) is octane, and so on ad infinitum . . . (or almost).

The Linus Paulings amongst us will have noticed that since a CH3 group (called a methyl group) has one free valency link, it can be used to replace any hydrogen atom, since that also has a valency of one. So, we need not have replaced the hydrogen atom at the end of the chain, we could have chosen one of the other hydrogen atoms in the middle. This can happen as often as we like, giving rise to a whole lot of different molecules with the same molecular formula. Thus, there are 5 forms of hexane, 18 forms of octane, and by the time we get to C20H42 there are 366,319 forms. These various forms with the same molecular formula are known as isomers.

The Michael Schumachers amongst us will have noticed something different - that octane is the primary constituent of petrol (oops, gasoline) and that this family of chemicals constitutes the paraffins, the primary chemical fuels that are used for a wide variety of purposes.

We can learn quite a lot just by looking at this family of paraffins. Methane is a gas, so is ethane; but by the time we get to hexane it is a liquid, and as the number of carbon atoms increases, so does the boiling point (conversion from liquid to gas) and the melting point (conversion of solid to liquid).

(to be continued)

continue to   Butter and margarine and other fats
to   Understanding the ketogenic diet



(checked: )
(update 1.1: 18 July 2002)
(issue 1: 5 January 1998)