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Macromolecules are large molecules composed of at least 100 atoms, commonly found in biology and biochemistry as proteins and nucleic acids. They exhibit unique physical properties and are created from a small set of monomers. Differences in macromolecule configurations can explain differences between organisms. Macromolecule complexes can also form through intermolecular forces.
The term macromolecule is used ambiguously to indicate a molecule composed of a “large number” of atoms, but more and more it is intended to indicate only those molecules composed of at least 100 atoms. Macromolecules may also less specifically be called polymers.
Most macromolecules are found in biology and biochemistry, in the form of long protein chains and nucleic acids such as DNA. This class of molecules is sometimes referred to as biomacromolecules or biopolymers.
It is rare to see a metal or crystal referred to as a macromolecule, even in cases where more than a hundred atoms are found connected to each other. Most commonly the term is applied to plastics, where myriad examples of the type exist.
Macromolecules are not simply an arbitrary distinction, as they exhibit many physical properties that distinguish them from common molecules. A particularly interesting property is their inability to dissolve in solution without external assistance (in the form of ions or salts, for example). Another is their tendency to break easily, often leading to erroneous assumptions such as the claim in the 1950s that DNA could never be longer than 5,000 base pairs. Although we now know this to be terribly wrong (strands of DNA can be in the tens of millions of base pairs), scientists at the time broke strands of DNA every time they took them under a microscope.
The building blocks of a macromolecule are known as monomers. Virtually all macromolecules are created from a very small set of only about fifty monomers. Being connected in different configurations, however, this small ensemble produces an extremely wide variety of macromolecules.
Many of the differences between organisms can be traced to the different configurations of macromolecules within the organism. Within a single organism, there can also be large differences between various macromolecules.
In usage, “macromolecule” can also refer to aggregates of multiple macromolecules, essentially producing supermacromolecules. These macromolecules are held together not by chemical bonds, but rather by intermolecular forces. Correctly, one could refer to these combinations as macromolecule complexes and the constituent components as subunits.
