http://www.ck12.org Chapter 26. Biochemistry
FIGURE 26.1
Structure of glucose, a typical carbohydrate.The glucose molecule illustrated in theFigure26.1 has a carbonyl on C-1 and –OH groups on each of the other
carbons. This way of representing the structure is known as a Fischer projection, named after the German chemist
Emil Fischer (1852-1919), who studied carbohydrate chemistry.
When dissolved in water, most of the glucose molecules are not actually present in the form represented in the
Figure26.1. Instead, one of the oxygen atoms near the end of the chain becomes bonded to the carbonyl carbon,
and a subsequent transfer of hydrogen results in the cyclic structure shown inFigure26.2.
FIGURE 26.2
Cyclic structure of glucose.Because six-membered rings are particularly stable, the oxygen atom used to form the ring will generally be on a
carbon atom that is five away from the carbonyl. If such a situation is not possible, five-membered rings can also be
formed. Rings of other sizes are generally less favorable than the open-chain form and will not be present in large
amounts.
Classes of Carbohydrates
There are several methods of classifying the various possible carbohydrates. The simplest carbohydrates consist of
a short chain or a single ring. These structures can be classified by the number of carbons in the chain. The terms