ABSTRACT
Ribosomes are macromolecular structures composed of ribosomal RNA (rRNA) and protein. They occur in large numbers in the cytoplasm where they translate messenger RNA into protein. Ribosomes have large and small subunits with characteristic sizes, described in terms of sedimentation (S) values. Prokaryotic ribosomes are 70S with 50S and 30S subunits. They contain three rRNAs (23S, 16S and 5S). Eukaryotic ribosomes are 80S and have 60S and 40S subunits. They contain four rRNAs (28S, 18S, 5.8S and 5S).
