In which cellular structure is double stranded circular DNA found?

Double-stranded circular DNA is found in mitochondria, which is a unique feature of these organelles. Mitochondria are known as the powerhouses of the cell because they generate ATP (adenosine triphosphate) through aerobic respiration. Unlike the linear DNA present in the nucleus, mitochondrial DNA (mtDNA) is circular and resembles the DNA of prokaryotes. This similarity supports the endosymbiotic theory, which proposes that mitochondria were once free-living bacteria that were engulfed by ancestral eukaryotic cells.

In contrast, the other cellular structures do not contain double-stranded circular DNA. The nucleus houses linear DNA organized into chromosomes, ribosomes are primarily composed of RNA and proteins essential for protein synthesis, and lysosomes contain enzymes for digestion but do not have any DNA. Therefore, the presence of double-stranded circular DNA is a defining characteristic of mitochondria, making them distinct among cellular organelles.