Atoms of hydrogen and oxygen and less frequently nitrogen, sulfur, or phosphorous bond to the carbon skeleton in a variety of ways to form small but complex molecules.
The four major types of macromolecules found in living cells—carbohydrates, lipids, proteins, and nucleic acids--are made of these smaller, repeating subunits called monomers. The monomers within one molecule are not always identical but they always have similar chemical structures. Monomers are joined together by a series of chemical reactions in a process called polymerization to form large, complex molecules called polymers. Poly means many. Another prefix you will run into later in your study of DNA testing is oligo. An oligomer is also a molecular made of repeating subunits but fewer in number than a polymer. For example, an oligonucleotide is a short change of nucleotides whereas a polynucleotide may have many, many nucleotide subunits. You may also run across the terms dimers, trimers, and tetramers—oligomers composed of two, three, and four monomers respectively.