What describes the structure of the DNA double helix?

The correct answer highlights that DNA is characterized by two strands coiled around each other, forming a double helix. This two-stranded structure is crucial to its function and stability, with the strands running in opposite directions (antiparallel) and held together by base pairs between complementary nucleotides (adenine with thymine and guanine with cytosine). The coiling of these strands provides the necessary compactness that allows DNA to fit within the nucleus of cells.

In contrast, the other options do not accurately represent the nature of DNA. For example, describing DNA as two parallel chains fails to capture the essential twisting nature of the double helix. The notion of a single strand that folds over itself misrepresents the double-stranded nature of DNA, while describing the structure as a helical formation without nucleotides neglects the fundamental components that make up DNA, which are the nucleotides that contain the genetic code.