DNA and RNA are chemically very similar. The primary structures of both are linear polymers composed of monomers called nucleotides. DNA and messenger RNA function primarily as informational molecules, carrying information in the exact sequence of their nucleotides. Cellular RNAs range in length from about 22 to many thousands of nucleotides. Cellular DNA molecules can be as long as several hundred million nucleotides. These large DNA units in association with proteins can be stained with dyes and visualized in the light microscope as chromosomes, so named because of their stainability. Though chemically similar, DNA and RNA exhibit some very important differences. For example, RNA can also function as a catalytic molecule. As we will see, the different and unique properties of DNA and RNA make them each suited for their specific functions in the cell

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