Different sugars, such as D-glucose, N-acetylglucosamine, L-arabinose, and D-galactose, can serve as carbon and energy sources to cells through similar mechanisms of import and catabolism. They are processed by different sets of proteins, but typically show a uniform functional organization that aids in their discovery and investigation. Different sugars require similar types of biochemical transformations, with actions by sugar kinases, isomerases, aldolases, hydrolases, and oxidoreductases. In addition, they require a transport system, and that may feature upstream and auxiliary components and some regulatory system (see Rodionov, et al., PMID: 20836887). Typically, at least one of the enzymes catalyzing biochemical transformation of a sugar shows enough sequence similarity to a fully characterized homolog to indicate that some uncharacterized sugar utilization pathway has been found. It then becomes possible to use comparative genomics and strain-by-strain assay of sugar utilization profiles to infer protein function for multiple families with high accuracy.