Is it true that DNA in extant prokaryotic cells is circular?

The statement that DNA in extant prokaryotic cells is circular is indeed true. Prokaryotic organisms, which include bacteria and archaea, typically have a single, circular chromosome that resides in a region of the cell called the nucleoid. This structure distinguishes prokaryotic DNA from eukaryotic DNA, which is linear and found within membrane-bound nuclei.

The circular nature of prokaryotic DNA allows for efficient replication and organization of genetic material. During cell division, the circular chromosome can easily separate and be copied, which facilitates the rapid reproduction of prokaryotic cells. In addition, prokaryotes often have plasmids—small, circular pieces of DNA that can carry additional genes, such as those for antibiotic resistance.

Overall, the predominance of circular DNA in prokaryotes plays a significant role in the biology and evolutionary adaptation of these organisms.