Presence of circular DNA
Prokaryotic cells are characterized by the presence of circular DNA. This means that the genetic material of prokaryotes, such as bacteria, is organized into a single circular chromosome. This is in contrast to eukaryotic cells, which have linear DNA organized into multiple chromosomes.

Explanation:
- Prokaryotic cells are simple cells that lack a membrane-bound nucleus and other membrane-bound organelles. Instead, their genetic material is located in the cytoplasm in the form of a single circular chromosome.
- The circular DNA in prokaryotic cells is not associated with histone proteins like in eukaryotic cells. It is found in a region called the nucleoid, which is not enclosed by a membrane.
- The circular DNA in prokaryotes contains all the genetic information necessary for the cell to carry out its functions.
- In addition to the main circular chromosome, prokaryotic cells may also contain smaller circular pieces of DNA called plasmids. Plasmids contain extra genes that can provide advantages to the cell, such as antibiotic resistance.
- The circular DNA in prokaryotic cells allows for efficient replication and gene expression. The absence of a membrane-bound nucleus means that the DNA is readily accessible for transcription and translation processes.
- In contrast, eukaryotic cells have a true nucleus, which is surrounded by a nuclear membrane. Their DNA is organized into multiple linear chromosomes and is associated with histone proteins. This organization allows for more complex regulation of gene expression.

Conclusion:
Therefore, the presence of circular DNA is a characteristic feature of prokaryotic cells. This characteristic distinguishes them from eukaryotic cells, which have linear DNA organized into multiple chromosomes and a true nucleus.