All cells have DNA, a cell membrane, ribosomes and cytoplasm. Eukaryotic cells do contain a nucleus, but prokaryotic cells does not. Prokaryotic cells are only bacteria. Prokaryotic cells are small, but eukaryotic cells are larger. Eukaryotic cells are anything besides bacteria. The endosymbiotic theory states that certain organelles started as free-living bacteria, that were taken inside another cell. This could be true, since prokaryotes are ONLY bacteria, and prokaryotes are smaller than eukaryotes. Eukaryotes could possibly be composed of prokaryotes.