What is a key similarity between the DNA in eukaryotic and prokaryotic cells?

The choice that highlights a key similarity between the DNA in eukaryotic and prokaryotic cells is that the nucleotide structure is identical. Both types of DNA are composed of nucleotides, which consist of a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine). The way these nucleotides link together to form the backbone of DNA is fundamentally the same in both eukaryotes and prokaryotes, underscoring a shared molecular foundation for genetic material across different domains of life.

In contrast, the other options indicate specific differences between these two types of cells. For example, eukaryotic DNA does contain introns—non-coding sequences that are not present in prokaryotic DNA. Prokaryotic DNA is typically circular and consists of a single, closed-loop chromosome, while eukaryotic DNA is usually linear and organized into multiple chromosomes. Therefore, the correct answer reflects a fundamental similarity in the composition of the DNA molecules.