The common, everyday use of the word "size" usually refers to volume. We speak of how much space an object occupies. Although molecules occupy space like all objects, when we talk about the size of a molecule, we're talking about its mass.

Biological molecules vary widely in mass. Small biological molecules have masses as low as 50-75 atomic mass units. In contrast, proteins can have masses of several hundred thousand atomic mass units.

The prefix "macro-," meaning large, is an appropriate description of the molecules we'll explore in this Lesson. As we'll see, most macromolecules are composed of smaller molecules such monosaccharides, fatty acids, or amino acids, bonded together in specific ways. The identity and arrangement of the components of a macromolecule play a crucial role in determining its biological function.


  • Describe the important structural features of carbohydrates, lipids, and nucleic acids and proteins.
  • Explain several common functions of macromolecules.
  • List examples of each class of macromolecules (polysaccharides, fats, and proteins) that perform common functions.
  • Discuss the relationship between the structure and function of different classes of macromolecules.
Last modified: Friday, September 3, 2010, 1:44 PM