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.