ribosome

Protein-making machinery of the cell. Active ribosomes are either located on the endoplasmic reticulum (ER) of eukaryotic cells or dissolved in the cytoplasm (of any kind of cell), and are made of proteins and a special type of RNA, ribosomal RNA. They receive messenger RNA (copied from the DNA) and amino acids, and ‘translate’ the messenger RNA by using its chemically coded instructions to link amino acids in a specific order, to make a strand of a particular protein.

When they are not busy, ribosomes dissociate into a larger and a smaller subunit. X-ray crystallography has revealed that the functional centre in the large subunit, which catalyzes the formation of the new peptide bond, is made up exclusively of RNA. Thus, the ribosome is also an example of a ribozyme or RNA enzyme. This finding lends strong support to the hypothesis that the early evolution of life on Earth involved an RNA world stage.