In junior-high and high-school biology you learn that a cell contains a nucleus and mitochondria, but before the 1950s the exact layout and jobs of these parts were largely unknown. Albert Claude refined the ultracentrifuge and developed “cell fractionation,” a method that separates cellular material according to how fast it sinks in the spinning field. Christian de Duve analyzed each fraction for enzyme activity and discovered the degradative lysosome and the oxidative peroxisome. George Palade perfected electron-microscope techniques and produced detailed images of ribosomes—the site of protein synthesis—and of membrane systems such as the Golgi apparatus and the endoplasmic reticulum. Together, their work established the modern concept that a cell operates through a coordinated system of membrane-bound organelles. This paradigm shift fueled molecular biology, medicine, and pharmacology; many diseases, including cancer and metabolic disorders, are now interpreted as malfunctions of specific organelles.

Claude modified the German-built ultracentrifuge to achieve step-wise cell fractionation at 1,000–100,000×g, and electron-microscope examination of the fractions revealed that mitochondria and endoplasmic reticulum are membrane-delimited entities—an innovative view at that time. De Duve used the subcellular distribution of acid hydrolase activity (acid phosphatase) to identify the lysosome, and D-amino-acid oxidase activity to pinpoint the peroxisome, thereby introducing the concept of organelle-specific marker enzymes. Palade established glutaraldehyde fixation, osmium post-fixation, and resin-embedding ultrathin sectioning, leading to the identification of densely packed particles on rough ER membranes as ribosomes. By combining electron microscopy with pulse-chase radiolabeling, he mapped the migratory route of secretory proteins—rough ER → Golgi apparatus → secretory vesicles—now known as the secretory pathway. These techniques and concepts evolved into today’s standard toolbox in cell biology, structural biology, and molecular medicine, underpinning research on organelle disorders, autophagy, exosomes, and more.

Claude’s differential and density-gradient centrifugation quantified organelle-specific sedimentation coefficients and buoyant densities, providing a precise platform for subcellular fractionation. De Duve rigorously controlled for enzymatic composition and isolation artifacts, inferred proton-pump-driven acidification of the lysosomal lumen, and discussed the biogenetic route of β-oxidation-competent peroxisomes. Palade employed high-voltage TEM and cytochemical labeling to quantify ribosome density, laying the groundwork for the SRP-dependent co-translational translocation model. Collectively, their contributions constitute the conceptual bedrock for modern studies of membrane trafficking topology, AAA-ATPase-driven organelle maintenance, and autophagic flux assessment. Integration of fractionation with proteomics—enabled by their techniques—now underpins organelle-resolving analytics and spatially resolved drug targeting, extending to high-resolution studies of transcriptional and post-translational modifications.