What is the structure of DNA?

The structure of DNA is best described as a double helix. This means that DNA consists of two long strands of nucleotides that twist around each other, resembling a spiral staircase. Each strand is composed of a sugar-phosphate backbone with nitrogenous bases (adenine, thymine, cytosine, and guanine) attached. The bases on one strand pair with complementary bases on the other strand, forming the rungs of the helix. This unique structure is key to DNA’s function in storing genetic information and allows for the process of replication, where the double helix unwinds and separates to make copies of the genetic material.

The single strand option does not accurately represent the structure of DNA, as DNA naturally occurs as a double-stranded molecule. The triple helix structure has been proposed in certain specialized situations, such as with some forms of synthetic or altered DNA, but is not the standard structure for naturally occurring DNA. A flat sheet does not reflect the physical properties of DNA, which must be capable of tightly packing within a cell nucleus while also being able to unravel and interact with other biomolecules. Thus, the double helix is the correct and widely accepted representation of DNA's structure.