Macromolecules include carbohydrates, proteins, lipids, and nucleic acids. They are larger, with molecular weights ranging from hundreds of daltons (sucrose) to billions (some nucleic acids). These molecules all contain carbon atoms, and so belong to a group of what are known as organic chemicals. Third, they are held together largely by covalent bonds, which gives them important structural stability and forms the basis of some of their functions. And finally, carbohydrates, proteins, lipids, and nucleic acids are all unique to the living world. These molecular classes do not occur in inanimate nature. You won"t find proteins in rocks and if you do, you can be sure they came from some living organism. Most of these biological molecules are large polymers (poly, many ; mer, unit ) constructed by the covalent bonding of smaller molecules called monomers (table 3. 1). The monomers that make up each kind of biological molecule have similar chemical structures.