According to the Biology Department at Indiana University Southeast, all four of the primary biomolecules contain carbon. This includes nucleic acids, lipids, carbohydrates and proteins. All four of these biomolecules are large and complex molecules that take advantage of the ability for carbon atoms to form long chains.
Even simple, single-celled organisms are incredibly complex when compared with non-living things, such as rocks or minerals. Accordingly, complex molecules are required to keep them functioning. Carbon works as an effective "backbone" for such molecules, because carbon bonds readily with many other atoms and can form long chains. These long chains bond with other elements, such as oxygen, hydrogen, nitrogen, phosphorus and sulfur, to create the four primary types of biomolecule.
Lipids help organisms to form protective structures, construct cell membranes and provide the energy for many metabolic processes. Proteins are important structural biomolecules that are used by organisms to build muscles and as an emergency food source. Additionally, along with lipids, proteins play a role in the construction of cell membranes. Nucleic acids hold the hereditary information for an organism in the form of DNA and RNA molecules. Carbohydrates primarily serve as an energy source for organisms, but they also serve structural and protective roles in plants when they take the form of cellulose.