RIBOSOMAL SUBUNITS
All ribosomes consist of two subunits. One of them, which in mass is approximately twice as large as the other, in called a large subunit, and the other one, correspondingly, a small subunit. Each subunit contains a high-molecular rRNA and a certain amount of various proteins. Almost all of them are presented in a ribosome only in one copy. The large subunit can contain, together with the basic RNA, also molecules of small RNA. In eukaryotes it has sedimentation coefficient 60S and molecular mass 2820 KD. The small subunit of eukaryotic cytoplasmic ribosomes is characterized by sedimentation coefficient 40S and molecular mass 1400 KD.