80S ribosomes are composed of two subunits of different sizes. The larger (60-S) subunit is composed of 5-S rRNA, 5.8-S rRNA, 28-S rRNA and about 40 proteins. The smaller (40-S) subunit is composed of 18-S rRNA and about 33 proteins. 80S ribosomes play a central role in synthesizing proteins in eukaryotes.