Prokaryote

Definition

A single-celled organism lacking a membrane-bound nucleus and other membrane-enclosed organelles, with genetic material typically circular and localized in a nucleoid region. Prokaryotes comprise the domains Bacteria and Archaea, distinguished from eukaryotes by their simpler cellular architecture, smaller ribosomes (70S), and absence of mitochondria, chloroplasts, and endomembrane systems. The term reflects organizational grade rather than a monophyletic group.

Etymology

From Greek πρό (pró, "before") and κάρυον (káruon, "nut, kernel"), referring to the absence of a true nucleus (kernel).

Example

Wolbachia, a genus of alphaproteobacteria, are intracellular prokaryote symbionts that manipulate reproduction in numerous insect and arachnid hosts, including causing cytoplasmic incompatibility in Drosophila and parthenogenesis induction in parasitoid wasps.

Synonyms

• prokaryotic organism
• procaryote

Related Terms

• Eukaryote
• bacteria
• archaea
• Symbiosis
• microbiome
• Wolbachia
• endosymbiont
• nucleoid
• 70S ribosome

Usage Notes

The term describes cellular organization, not a clade; prokaryotes are paraphyletic with respect to eukaryotes. In entomology and arachnology, prokaryotes are critical as gut symbionts (e.g., hindgut bacteria in termites digesting cellulose), reproductive manipulators, and pathogens. Avoid using "prokaryote" as a taxonomic rank; prefer "domain Bacteria" or "domain Archaea" for formal classification. Contrast with "prokaryotic" (adjective form).