What cellular component contains double-stranded circular DNA?

The mitochondrion is the correct answer because it is unique among cellular organelles in that it contains its own double-stranded circular DNA. This type of DNA is similar to that found in prokaryotic cells, supporting the endosymbiotic theory, which suggests that mitochondria originated from free-living bacteria that were engulfed by ancestral eukaryotic cells. This circular DNA encodes some of the proteins required for mitochondrial function, particularly those involved in the electron transport chain and energy production.

In contrast, the other options do not contain double-stranded circular DNA. The Golgi apparatus is involved in modifying and packaging proteins but does not have any DNA. The nucleus contains linear double-stranded DNA, which is organized into chromosomes and houses the genetic material for the cell's entire genome. Peroxisomes are organelles involved in lipid metabolism and detoxification processes but also do not contain any DNA. Therefore, the presence of double-stranded circular DNA is a defining characteristic of mitochondria among these organelles.