= Prokaryote
{wiki}
= Prokaryotic
{synonym}
A <prokaryote> is an <organism> whose <biological cells> lack a membrane-bounded <cell nucleus>. The <DNA> of its <chromosomes> occupies a <nucleoid> within the <cytoplasm>. <Bacteria> and <archaea> have this cellular organization. Both contain <ribosomes> that perform <biological translation> and a selective <cell membrane>; neither is a bag of unorganized chemicals. See https://openstax.org/books/biology-2e/pages/4-2-prokaryotic-cells[OpenStax Biology 2e, 4.2: prokaryotic organization].
The word <prokaryotic> describes organization, not a single exclusive <clade>. Grouping <bacteria> and <archaea> by the absence of a <cell nucleus> is useful for comparing <biological cells>, but does not establish that they share a more recent ancestor with one another than either does with <eukaryotes>. See <three-domain system> and <two-domain system> for the different ancestry models.
<Prokaryotic> does not mean membrane-free. <Cyanobacteria> contain internal <thylakoid> membranes for <oxygenic photosynthesis>, despite lacking <chloroplasts> and a <cell nucleus>. Many <prokaryotes> have circular <chromosomes>, but circular shape and a single <chromosome> are not defining requirements. See https://openstax.org/books/biology-2e/pages/22-2-structure-of-prokaryotes-bacteria-and-archaea[OpenStax Biology 2e, 22.2: bacterial and archaeal structures].
\Image[/prokaryote-eukaryote-cell-organization.png]
{title=Cell organization: an <Escherichia coli> example beside a nucleated <animal> cell}
{description=Original schematic cross-sections, not micrographs and not at exact relative scale. Both show a <cell membrane>, <cytoplasm>, <DNA> and <ribosomes>. The <Escherichia coli> envelope is simplified: its outer membrane is omitted. The <animal> cell additionally shows a <nuclear envelope> and <mitochondria>; many other structures are omitted. The outlined <nucleoid> is a region, not a membrane.}
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