During the period 1926–1955, structural biology shifted from qualitative sketches to quantitative assessments of macromolecules; measurements of size, diffusion, and optical properties defined mechanistic models of protein architecture. The elucidation of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) structures anchored molecular biology in a structural framework, linking genetic information to biomolecular form and establishing base-pairing and helix motifs. Analytical proteomics and enzymology enabled quantitative structure–function mappings, connecting chemistry to biological roles and shaping early mechanistic understanding of enzymes and binding interactions. Historical Significance: The era’s landmark papers formalized core structural concepts. The structure of proteins introduced alpha-helix and beta-pleated sheet as fundamental secondary motifs, providing a concrete framework for folding and function. The Molecular Structure of Nucleic Acids proposed the DNA double-helix with base pairing, reframing biology as a structural discipline and underpinning later genetics and biotechnology. The Determination of Enzyme Dissociation Constants offered a quantitative metric for enzyme–substrate interactions, bridging chemistry and biology and laying groundwork for modern enzymology and structure–function analyses; the early theory of antibody formation highlighted modular organization and antigen–antibody interactions as precursors to structural immunology.