Imagine shrinking yourself over a million times smaller. If you could, you would then be the size of a virus! You have entered a fantastic realm, where light has no meaning, because a virus is smaller than light itself! The figure to the left is a comparison of the different scales of our submicroscopic world. Molecules and atoms are 100 to 1000 times smaller than viruses, and only highly sophisticated equipment can "see" them. If you want to see the entire figure, click on the hyperlink below: Visit Scale Figure Atoms are the smallest, discrete unit of matter. That's because the parts of different atoms are pretty much the same. Atoms differ by the number of protons, which gives each element particular chemical properties. Two or more atoms bonded in some way make a molecule. This is where the fun starts. Although there are many different naturally occurring molecules, a huge number of unique molecules are put together by the wonderful thing we call LIFE. Life molecules are chiefly made of a just handful of small atoms: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur (CHNOPS). To be sure, other elements are used in life and are very important, but the vast majority of molecules in us, and all living things, contain CHNOPS. Molecular Biology Factoid: When scientists want to label DNA, they use a radioactive tag on phosphorus. When labeling proteins, they put a tag on sulfur atoms. That's because phosphorus is unique to the DNA sugar-phosphate backbone and is not in proteins. Likewise, sulfur is unique to proteins and is not in DNA. By radioactively labeling either protein or DNA, early molecular biologists determined that it was DNA that carried the instructions for life, not proteins.