The ribosome, which builds all proteins, runs on RNA rather than protein
Every cell on Earth relies on ribosomes to read genetic instructions and string amino acids into proteins. The surprise is in the machinery: the chemical step that joins each amino acid to the next is carried out not by protein but by ribosomal RNA, making the ribosome a ribozyme and a clue to life's early chemistry.
A ribosome consists of a small and a large subunit, each built from ribosomal RNA plus many proteins. It clamps onto a messenger RNA and reads it three letters at a time. Transfer RNAs ferry in amino acids, each matching a codon through its anticodon, and the ribosome links them into a growing chain, which later folds into a working protein. Translation proceeds through initiation, elongation, termination and recycling. Every message begins at the start codon AUG and ends at UAA, UAG or UGA, codons no transfer RNA recognises, which signals the job is done. Several ribosomes can read one message simultaneously, forming a polysome.
Ribosomes in bacteria, archaea and eukaryotes resemble one another remarkably closely, strong evidence of shared ancestry, yet they differ in size, sequence and protein-to-RNA ratio. Those differences matter in medicine: some antibiotics jam bacterial ribosomes while leaving human ones untouched. Mitochondria have their own ribosomes that behave more like bacterial ones, echoing their origin as captured bacteria, and chloroplasts have distinct versions too.
The Romanian-American cell biologist George Emil Palade first saw them in the mid-1950s as dense granules under an electron microscope, and for a while they were called Palade granules. The name ribosome emerged at a 1958 symposium, where Howard Dintzis reported that participants could not agree what 'microsomes' meant; the new word, he wrote, had a satisfactory ring and a pleasant sound, and would end the confusion.
Two Nobel Prizes followed. In 1974 Albert Claude, Christian de Duve and Palade shared the prize in Physiology or Medicine for the discovery. In 2009 Venkatraman Ramakrishnan, Thomas Steitz and Ada Yonath won the chemistry prize for revealing the ribosome's atomic structure and mechanism, work built on X-ray crystallography and cryo-electron microscopy.
Source: Ribosome
