Polar molecules have opposite charges at either end. “Polar” refers to the positive and negative sides of the molecule. If a molecule is polar, it will be attracted to other polar molecules; for example, water is a polar molecule. This can affect a wide range of chemical interactions, including whether a substance will dissolve in water, the shape of a protein, and even the complex structure of DNA.

Molecules are made of specific combinations of atoms. For example, carbon dioxide is made of one carbon atom and two oxygen atoms; water is made of two hydrogen atoms and one oxygen atom—with all the atoms joined by chemical bonds. Complex molecules such as starch may have hundreds of various atoms linked together in a specific pattern. Four molecules are referred to as bioorganic because they are essential to living organisms and contain carbon: nucleic acids, proteins, carbohydrates, and lipids. These molecules are all large, and they are formed by a specific type of smaller molecule, known as a monomer.