26.1. Carbohydrates http://www.ck12.org
FIGURE 26.1
Bread, potatoes, pasta, and vegeta-
bles are high-carbohydrate foods that en-
durance athletes often consume in large
quantities in a procedure called carbo-
loading.Carbohydrates are the most abundant source of energy found in most foods. The simplest carbohydrates are also
called simple sugars and are plentiful in fruits. Amonosaccharideis a carbohydrate consisting of one sugar unit.
Common examples of simple sugars or monosaccharides are glucose and fructose. Glucose is also referred to as
corn sugar or grape sugar and is abundant in plants and animals. Fructose occurs in many fruits and is also found
in honey. They are structural isomers of one another. Glucose has a carbonyl on the end of its chain, so it is an
aldehyde, while the carbonyl of fructose is on an interior carbon, making it a ketone (Figure26.2).
FIGURE 26.2
Glucose and fructose are monosaccha-
rides, or simple sugars.Glucose and fructose are both very soluble in water. In aqueous solution, the predominant forms are not the straight-
chain structures shown above (Figure26.2). Rather, they adopt a cyclic structure (Figure26.3). Glucose forms a
six-membered ring, while fructose forms a five-membered ring. Both rings contain an oxygen atom.
FIGURE 26.3
The cyclic form of sugars is the favored
form in aqueous solution.