The bacterial ribosome is a cytoplasmic nucleoprotein particle whose main function is to serve as the site of mRNA translation and protein synthesis. The ribosome has a mass of about 2.5 MDa, with RNA accounting for 2/3 of the mass. It consists of two subunits denoted 30S (small subunit) and 50S (large). When joined, the ribosome has a sedimentation coefficient of 70S as opposed to 80S due to tertiary structure. The subunits' shape and arrangement are illustrated below.
Click on a subunit to learn more.