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Prokaryotes are organisms whose cells lack a nucleus and other organelles. Prokaryotes are divided into two distinct groups: the bacteria and the archaea, which scientists believe have unique evolutionary lineages.
Most prokaryotes are small, single-celled organisms that have a relatively simple structure. Prokaryotic cells are surrounded by a plasma membrane, but they have no internal membrane-bound organelles within their cytoplasm. The absence of a nucleus and other membrane-bound organelles differentiates prokaryotes from another class of organisms called eukaryotes.
Most prokaryotes carry a small amount of genetic material in the form of a single molecule, or chromosome, of circular DNA. The DNA in prokaryotes is contained in a central area of the cell called the nucleoid, which is not surrounded by a nuclear membrane. Many prokaryotes also carry small, circular DNA molecules called plasmids, which are distinct from the chromosomal DNA and can provide genetic advantages in specific environments.
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