Carbohydrates, lipids, nucleic acids and one other group make up the four major classes of biological macromolecules. The fourth is:

1. Macromolecules are the large carbon-based molecules a cell builds from monomers. 2. There are four major classes of them: carbohydrates, lipids, proteins and nucleic acids. 3. Vitamins, steroids and minerals are not classes of macromolecule; steroids are one kind of lipid. 4. So the missing fourth class is proteins. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 3 'Biological Macromolecules', sections 3.1-3.5_