The Chemistry of Carbohydrates

Let’s start with a quiz.

Based purely on the name, what do you reckon a carbohydrate is? Hint: carbohydrates are one of the few classes of chemical whose name tells you exactly what they are.

Well, if “carbo” stands for carbon, and of course “hydrate” refers to water, then we arrive at the conclusion that a carbohydrate is carbon + water.

In fact, you’d be right. Let’s write it as a chemical symbol and see how we go: CH2O

As it happens this is quite right – every carbohydrate can br educed to this simple formula. Let’s consider glucose – the simplest carbohydrate:

Its formula is C6H12O6 – if we divide everything by 6 we get back to CH2O

In fact carbohydrate molecules occur in blocks of 6 carbons (called “saccharide” units) – so glucose, a monosaccharide is C6H12O6, and sucrose, a disaccharide is C12H24O12

And they just get bigger, with units up into the hundreds or thousands. The mono and di-saccharides are simple carbohydrates and the higher numbers are complex carbohydrates.

As it happens, glucose (ie glycogen) is the fuel that our body runs on. Before anything that we eat can be used as fuel, it must first be converted to glucose. The ease with which this process happens is recognised as being a major factor in determining whether we put on weight or not and is linked with diabetes.

Not all carbohydrates are digestible, however. Like trees. Or cotton. But more on this later – and how they help stiffen your clothes when ironed.


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