RNAribosome

RNAribosome is a term used to refer to the ribosome in which ribosomal RNA (rRNA) forms the central structural and catalytic component of the particle. In all life forms, ribosomes are ribonucleoprotein complexes consisting of rRNA and proteins; the rRNA molecules provide the core architecture of the active site and drive key catalytic steps, while ribosomal proteins support assembly, stability, and regulation.

Composition and structure vary by domain. In bacteria, the functional ribosome is 70S, made of a 50S subunit containing the 23S and 5S rRNA and about 31 proteins, and a 30S subunit containing the 16S rRNA and about 21 proteins. In eukaryotes, the cytosolic ribosome is 80S, with a 60S subunit housing the 28S, 5.8S, and 5S rRNAs and a 40S subunit containing the 18S rRNA. Mitochondria and chloroplasts have their own ribosomes, which often resemble bacterial counterparts. rRNA genes are organized and transcribed to precursor rRNAs that are processed and assembled with ribosomal proteins through a multi-step biogenesis pathway.

Mechanism and function. The ribosome translates mRNA into protein by matching codons with tRNA anticodons, stepping through the A, P, and E sites. The peptidyl transferase center, responsible for peptide bond formation, is formed by rRNA in the large subunit, making the ribosome a ribozyme. Fidelity largely arises from the decoding center within the small subunit and from tRNA selection and proofreading during elongation.

Clinical and evolutionary notes. The rRNA components are highly conserved and widely used in phylogenetics. Because bacterial ribosomes differ from eukaryotic ones, many antibiotics target bacterial rRNA or rRNA–protein interfaces, enabling selective toxicity.