Insulin is a protein hormone, and as such, its primary structure is a chain of amino acids. While it doesn't contain traditional "functional groups" like aldehydes, ketones, or carboxylic acids, it does have several amino acid side chains that contribute to its function:

* Aromatic rings: Tyrosine, phenylalanine, and tryptophan residues contribute to the hormone's structure and interactions with its receptor.

* Charged residues: Lysine and arginine residues are positively charged and participate in electrostatic interactions. Glutamic acid and aspartic acid residues are negatively charged and also contribute to electrostatic interactions.

* Polar residues: Serine, threonine, and asparagine residues contribute to hydrogen bonding interactions.

* Hydrophobic residues: Leucine, isoleucine, valine, and alanine residues contribute to hydrophobic interactions, which help to fold the protein into its correct three-dimensional shape.

It's important to note that the specific arrangement of these amino acid side chains, along with the overall tertiary structure of insulin, is crucial for its biological activity.

Therefore, while insulin doesn't contain traditional functional groups, it has a unique composition of amino acid side chains that contribute to its structure and function.