Prokaryotic cells lack a nucleus. Bacteria and members of the domain Archaea are prokaryotes, while plants, animals, protists and fungi are eukaryotes. Prokaryotic cells lack the membrane-bound organelles found in eukaryotic cells.
Prokaryotic cells are much smaller and much simpler than eukaryotic cells.
The two types of cells do have some similarities, however. Prokaryotic cells and eukaryotic cells both contain cytoplasm and have ribosomes for producing proteins. Both types of cells also contain DNA, but the DNA found in prokaryotic cells is circular while the DNA found in eukaryotic cells is linear.
Bacteria is a common example of a prokaryotic cell.