The side chain of which amino acid contains a guanidino group?
Arginine accurately describes the structural composition or molecular organization asked about in this question. In Amino Acids Basics, knowledge of molecular structure is directly linked to understanding biological function. The specific arrangement of chemical components in Arginine determines its physical properties, biological activity, and interactions with other molecules. The other options (Histidine, Lysine, and Tyrosine) describe different structural arrangements, incorrect stoichiometry, or compositions of different biological molecules.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 3