Just One Molecule

However, life is different for objects as small as a single molecule. Since many important tasks in biology are performed one molecule at a time, it is important to understand what happens in this microscopic world. Here, lengths are measured in nanometers, and a typical length is a thousand times smaller than the width of a human hair.

A typical biological molecule is ribonucleic acid, or RNA. An RNA molecule contains roughly two hundred atoms arranged in a long, linear structure. Since we are interested in the behavior of the molecule as a whole, we will ignore most of the atomic details such which carbon atom is bonded to which nitrogen atom. In fact, physicists do this quite often in studying complex phenomena. It is very much like drawing

to represent one of the world's great monuments; it captures the essential aspects while ignoring the complicated details. For a long linear RNA molecule, we will draw

In addition to neglecting the atomic details, we also hide the millions of water molecules surrounding the RNA molecule even though they play a crucial role in this system's behavior.