Responsible for proteins that go into solution in the cytoplasm or form important cytoplasmic structural or motile elements. Responsible for proteins that insert into membranes or are packaged into vesicles for storage in the cytoplasm or export to the cell exterior. All ribosomes within one cell are identical. A substantial fraction of ribosomes are dissociated into free subunits in the cell. Prokaryotic and eukaryotic ribosomes differ in composition.
Mitochondrial ribosomes resemble prokaryotic ribosomes.