Chemistry · Chemistry of Life

The above structure represents histidine, as it has five carbon ring structures along -CH₂ attached as a radical group.

Proline is unique because its side chain forms a ring structure that links back to the nitrogen atom of its amino group, making it an imino acid, not a standard amino acid with a free alpha-amino group.

The image provided displays the chemical structure of the amino acid histidine, characterized by its unique imidazole ring side chain. This five-membered ring contains two nitrogen atoms, which gives histidine its basic properties. This specific side chain is absent in the other listed amino acid.

Glycine is the simplest amino acid, with a side chain consisting of just a single hydrogen atom. Its structure is a central carbon bonded to two hydrogen atoms, an amino group, and a carboxyl group, which is a much simpler, non-cyclic structure than the one presented.

Lysine has a long, linear side chain made up of four methylene (-CH₂) units and a terminal primary amino group (-NH₂). This basic, positively charged side chain is an open chain structure, distinctly different from the imidazole ring in the provided image.