Understanding the ribosome was a progression of scientific inquiry that built upon new technologies. Before the ribosome was named or its function understood, it was simply an uncharacterized part of a cellular fraction. The discovery began with the isolation of tiny, unidentified particles, which laid the groundwork for later scientists to bring these structures into focus and reveal their importance in biology.
The Foundational “Microsome” Discovery
The first step toward identifying ribosomes was taken in the 1930s and 1940s by cell biologist Albert Claude. At the Rockefeller Institute, Claude developed differential centrifugation, a technique that separates a cell’s components by size and density. This process involves grinding up cells and spinning the mixture in a centrifuge at progressively higher speeds.
Through this method, Claude isolated a fraction of very small, dense granules he called “microsomes,” determining they were rich in ribonucleic acid (RNA). While he had successfully isolated what we now know contained ribosomes, the technology of the time did not allow for their precise visualization as distinct cellular structures.
George Palade’s Definitive Identification
The definitive identification of ribosomes came in the mid-1950s from George E. Palade, a colleague of Claude’s at the Rockefeller Institute. Palade used the advancing technology of electron microscopy, which offered far greater resolution than previously possible. This allowed him to visualize the “microsomes” within the context of the cell itself.
Palade improved techniques for preparing biological samples, which preserved cellular structures for electron microscopy. His detailed micrographs, first published in 1955, revealed that Claude’s microsomes were composed of dense, granular particles that were universal components of cells. He observed these particles both free in the cytoplasm and attached to the membranes of the endoplasmic reticulum, establishing them as distinct organelles. For this work, Palade shared the 1974 Nobel Prize in Physiology or Medicine with Albert Claude and Christian de Duve.
The Significance of the Discovery
With the physical structures identified, the next step was to understand their function and give them a name. The term “ribosome” was proposed in 1958 by Richard B. Roberts to resolve confusion with the term “microsome,” which referred to the entire fraction. The new name reflected the particle’s composition: “ribo” for its ribonucleic acid content and “some” from the Greek word for body.
Subsequent research confirmed the ribosome’s function as the site of protein synthesis. This discovery provided the physical basis for how genetic information in messenger RNA (mRNA) is translated into the proteins that carry out cellular functions. The identification of the ribosome connected genetics with the protein-based machinery of the cell, providing a foundation for modern molecular biology and medicine.