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.
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