Have you looked at a nutrition label lately? Today's FDA-approved food labels describe nutritional content according to the major classes of biological molecules: fats, carbohydrates, and proteins. Many of the biological molecules in food products are macromolecules. Macromolecules are very large molecules with molecular masses as high as several million atomic mass units. Most macromolecules are polymers of small, similar molecules covalently bonded together.

One class of carbohydrates is the polysaccharides. Polysaccharides are polymers of the simple sugar units called monosaccharides that we studied earlier. Fats are combinations of fatty acids, a small molecule called glycerol, and sometimes an organic phosphate. Proteins are polymers of amino acids. All three classes of macromolecules are formed from condensation reactions between monomers. A condensation reaction is one where two molecules are joined by the elimination of a small molecule, like water.

We'll explore three important roles shared by the classes of macromolecules. Certain macromolecules are used primarily for energy. Others give an organism its structural support. Some macromolecules are involved in the transport of small molecules from one cell, tissue, or organ to another.

We're going to look at each class of macromolecules individually. We'll start with the structure and function of polysaccharides, continue with the structure and function of fats, and conclude with the structure and function of proteins. Keep in mind that a macromolecule's function is closely related to its structure. As we consider the three classes of macromolecules, pay close attention to the structural similarities of macromolecules of different classes but with similar functions.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education