The cells of all the living organisms are made of many complex molecules called macromolecules, such as proteins, nucleic acids (RNA and DNA), carbohydrates, and lipids. And these macromolecules that distinguish the living matter from inanimate material are all composed of carbon atoms bonded to one another and to atoms of other elements. Hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P) are other common ingredients of these compounds.
For historical reasons, the compounds containing carbon are said to be organic, and the branch of chemistry that specializes in the study of carbon compounds is called organic chemistry.
Different species of organisms, and different individuals within a species, are distinguished by variations in their organic molecules. It is the unique properties of carbon that allow it to form covalent bonds to as many as four different atoms, making this versatile element ideal to serve as the basic structural component, or “backbone,” of these organic molecules.
The organic molecules important for life include relatively small monomers as well as large polymers. This is because carbon skeletons can vary in length, branching, and the ring structure. The functional groups of organic molecules also involve in various chemical reactions.