Side chain

The R symbol was introduced by 19th-century French chemist Charles Frédéric Gerhardt, who advocated its adoption on the grounds that it would be widely recognizable and intelligible given its correspondence in multiple European languages to the initial letter of "root" or "residue": French racine ("root") and résidu ("residue"), these terms' respective English translations along with radical (itself derived from Latin radix below), Latin radix ("root") and residuum ("residue"), and German Rest ("remnant" and, in the context of chemistry, both "residue" and "radical").

Side chains have noteworthy influence on a polymer's properties, mainly its crystallinity and density.

[4] In proteins, which are composed of amino acid residues, the side chains are attached to the alpha-carbon atoms of the amide backbone.

The amino acid side chains are also responsible for many of the interactions that lead to proper protein folding and function.

Nonpolar/polar interactions can still play an important part in stabilizing the secondary structure due to the relatively large amount of them occurring throughout the protein.