I want to write a sentence along the lines of:
There are four ____ in biochemistry: proteins, lipids, carbohydrates and nucleic acids.
Does a specific technical term exist that I can use to fill the void? Or am I relatively free in my choice?
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I don’t know what your background is. Maybe it is organic chemistry, where the term functional group is used in a very specific way and using what would seem to be a synonym instead is wrong. Maybe it is biology (taxonomy) where it makes a big difference if a ‘group’ is an order, a family, a genus or something else.
The typical primary metabolites in biochemistry — carbohydrates, peptides/proteins, nucleic acids and lipids — do not have an overarching, widely accepted technical umbrella term. You can call them groups, classes, kinds or even types and be well understood.
If I had to suggest something, I would go with classes of primary metabolites. But I wouldn’t call that a strict technical term like functional group (organic chemistry) or species (taxonomy).
Adding on to what Jan mentioned I looked it up in a few of the well-known textbooks. (Emphasis mine.)
Alberts et al. Molecular Biology of the Cell 6ed, p47 writes
"four major families of small organic molecules"
Berg & Stryer Biochemistry 7ed, p2 is a bit more careful
[...] two different classes of molecules: large molecules such as proteins and nucleic acids, referred to as biological macromolecules, and low-molecular-weight molecules such as glucose and glyccerol, referred to as metabolites [...]
Lehninger Principles of Biochemistry 6ed, p15 writes
Many biological molecules are macromolecules... shorter polymers are called oligomers... Table 1-1 shows the major classes of biomolecules in an E. coli cell. [Entries in Table 1-1: Water, proteins, nucleic acids, polysaccharides, lipids, monomeric subunits and intermediates, inorganic ions.]
Voet & Voet Biochemistry 4ed, p15 writes
[...] E. coli, and living things in general, contain only a few different types of macromolecules: proteins, [...] nucleic acids, and polysaccharides. [...] Lipids, the fourth major class of biological molecules, are too small to be classified as macromolecules but also have a modular construction.
Two weeks ago I suggested "classes of biomolecules" in my comment. In lieu of what I have quoted above, I think that might be a little bit imprecise since there are more types of biomolecules than simply those four classes. So, "major classes of biomolecules" would be a good idea.