Macromolecules are large molecules composed of thousands of covalently connected atoms. Carbohydrates, lipids, proteins, and nucleic acids are all macromolecules. Macromolecules are formed by many monomers linking together, forming a polymer. Carbohydrates are composed of carbon, oxygen, and hydrogen. They are typically composed of thousands of atoms or more. The four major classes of biological macromolecules are carbohydrates, lipids,proteins, and nucleic acids.