Any cellular organism that lacks a distinct nucleus. Organisms classified in the domains Bacteria (including blue-green algae, or cyanobacteria) and Archaea are prokaryotes; all other organisms are eukaryotes and are placed in the domain Eukarya. Prokaryotic cells lack a nuclear membrane and most of the components of eukaryotic cells. The cytoplasm includes ribosomes that carry out protein synthesis and a double-stranded DNA chromosome, usually circular. Many prokaryotes also contain additional circular DNA molecules called plasmids. The flagella are distinct from those of eukaryotes in design and movement.

This entry comes from Encyclopædia Britannica Concise.
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