The Ribosome

Ribosomes are the actual site for protein synthesis in all types of cells. Here, mRNA and aminoacyl-tRNA meet during translation of the genetic message. In addition to providing the structural framework for the decoding process, the ribosome itself contains the catalytic centre responsible for formation of the peptide bond, the so-called peptidyl transferase centre.

The ribosomes were first discovered in the early 1940s but their role in protein synthesis first became apparent more than a decade later. The name "ribosome" was given to the particles in 1958.

Ribosomes from different types of cells have the same basic structure but vary in size. Thus, all ribosomes are composed of two subunits. Each subunit contains a characteristic set of rRNA (ribosomal RNA) and ribosomal proteins. In the case of the eukaryotic ribosome, the two subunits are called the 40S (Svedberg unit) and the 60S subunits. The 40S subunit contains one rRNA molecule, 18S rRNA, and around 35 proteins, while the 60S subunit contains three rRNA species, 5S, 5.8S and 28S rRNA, and approximately 45 proteins.

Together, the two subunits make up the complete 80S ribosome. The interface region between the two subunits provides the active surface at which mRNA and aminoacyl-tRNA interact.