What is a characteristic of the DNA double-helix structure?

The correct answer highlights a fundamental aspect of the DNA double-helix structure, which is the 3.4 Å (angstrom) distance between adjacent base pairs. This specific measurement delineates the vertical distance between successive pairs of complementary nucleotides along the axis of the helix. In the structural model of DNA, this distance results from the spatial arrangement and hydrogen bonding between the nucleotide bases, which are stacked on top of one another, contributing to the helical form of DNA.

This characteristic is vital in understanding the uniformity of the helical structure and how base pairing influences the overall dimensions of the DNA molecule. The regularity imparted by this distance is critical for the maintenance of the helical twist and stability of the double helix, as well as its interactions with proteins during processes such as replication and transcription.

In contrast, the other options inaccurately describe features of the DNA double-helix structure. For instance, the DNA strands are actually antiparallel, meaning they run in opposite directions. While DNA predominantly exhibits a right-handed helical geometry, there are instances of left-handed helices (such as Z-DNA), which makes the notion of it being right-handed only misleading. Lastly, the structure of DNA is not a