What do you call a molecule that is composed of two structurally similar subunits?

A molecule composed of two structurally similar subunits is termed a dimer. Dimers are specific types of oligomers, which are molecules made up of multiple repeating units or subunits. In the case of dimers, these two subunits can be identical or similar in structure, allowing them to bond together to form a more complex molecular structure.

For example, in biochemistry, certain proteins exist as dimers, where two polypeptide chains come together to function as a single unit. This can often be crucial for the protein's functionality, stability, or activity. Understanding dimers is important in various biological processes, such as enzyme function and cellular signaling pathways.

The other terms in context do not describe this structural relationship. Diabetes refers to a metabolic disorder, a dichotomous key is a tool for identifying organisms based on characteristics, and diffusion describes a physical process of movement of molecules from an area of high concentration to an area of low concentration. Thus, dimer is the precise term that captures the essence of two similar subunits forming a single molecule.