Macromolecules are very large molecules created by the polymerization of small units called monomers. Most of the macromolecules are present in everyday life, for instance in food (although nucleic acids are not considered food macromolecules).

There are several types of biological macromolecules:

All macromolecules, except lipids, are polymers. A polymer is a long molecule composed of chains of monomers (Figure 1A). Monomers are small molecules that serve as building blocks of polymers (Figure 1C).

In addition, there are also oligomers in nature. Oligomers are molecular complexes made out of a few monomer units, as opposed to polymers, which are theoretically unlimited. Dimers and trimers are, for instance, oligomers composed of two and three monomers, respectively, such as lactose in milk (Figure 1B).

Three images of chemical structures. Image “A” presents three chained structures of glucose unit, where the middle one is put in square brackets with a number 300 to 600. Image “B” presents glucose and galactose structures joined together. Image “C” presents one structure of glucose.

Figure 1. Examples of polymers, oligomers, and monomers: A) Amylose, a polymer found in starch; B) Lactose, an oligomer found in milk; C) Glucose.

However, in biochemistry, an oligomer usually refers to a macromolecular complex formed by non-covalent bonding of a few macromolecules, like nucleic acids or proteins. Clear examples of this are oligomers related to many neurodegenerative diseases, such as the alpha-synuclein aggregations in Parkinson's disease.