Cells

A monosaccharide—the prefix mono means “one”—is the smallest type of carbohydrate molecule. There are many types of monosaccharide molecules, the two most common being glucose and fructose. Monosaccharides, particularly glucose, are important energy sources for cells. In addition to providing energy, the carbon atoms in glucose can be used by the cells to build other important molecules, like fatty acids and amino acids. If the monosaccharides are not used by the cells immediately, they can be stored in larger carbohydrate molecules to be used later.

illustration showing that glucose, fructose, and galactose all have the same chemical formula, C subscript 6 H subscript 12 O subscript 6

Text Version

When dissolved in water, like inside a cell, monosaccharide molecules form a ring structure. Notice that glucose, fructose, and galactose all have the same chemical formula, C6H12O6. However, the differences in the arrangement of the atoms and bonds give each of the molecules a unique shape. The shape of a molecule determines how molecules function and react within a cell.

Disaccharides are carbohydrate molecules made up of two monosaccharide molecules bonded together. Monosaccharides and disaccharides are classified as simple carbohydrates. Most simple carbohydrates have a sweet taste, and they are collectively referred to as "sugars" in biology. Table sugar, called sucrose, is a disaccharide that you probably use every day. It is made up of one fructose molecule and one glucose molecule bonded together. Lactose, the major sugar in milk, is made of one glucose molecule and one galactose molecule bonded together. Maltose is a disaccharide produced during the digestion of starch. It is made of two glucose molecules.

Sucrose Table sugar = glucose + fructose

Lactose Major sugar in milk = glucose + galactose

Maltose Product of starch digestion = glucose + glucose

Text Version

Polysaccharides are carbohydrate polymers made up of hundreds to thousands of...