Subunit composition of Eukaryotic & Prokaryotic ribosomes

Ribosome subunits comprise one or two rRNA molecules, plus a variable number of proteins. Combinations of rRNAs and proteins typically have a smaller sedimentation rate (S) than their component parts, due to condensation. In eukaryotes, the complete 80S monosome comprises a 40S Small Subunit (SSU) that includes the 18S rRNA, and a 60S Large Subunit (LSU) that includes the 28S, 5.8S, and  5S rRNAs. Prokaryotic ribosomes are somewhat smaller, but include analogous subunits.

Figure 2012 TA Brown, Introduction to Genetics (1st ed.); additional text 2013 by Steven M. Carr