The basic components of our DNA. Adenine, thymine, guanine and cytosine are the nitrogenous bases, encoding the information which we call genes. They compose the 'rungs' of the ladder. The phosphate backbone repeats in a long-chain polymer to create the two twisting helices, giving DNA its distinctive shape.

Detail of the phosphate backbone, showing how the tetrahedron-shaped phosphate groups alternate with deoxyribose sugars.

Here we see a nucleosome inside the cell's nucleus. A nucleosome is a type of protein which acts as a spindle around which the DNA strand is wound. A series of these proteins stack together, twisting into a larger helical strand. This strand knots up upon itself over and over again to form a chromosome. Spirals becoming greater spirals, spanning orders of magnitude in scale.

A representation of the soluble surface of a DNA segment. Notice that the two helices are not symmetrically placed; they form a wide groove on one side and a narrow groove on the other. This forms two distinctly different locations for molecules to bind to the nitrogenous bases as the cell goes about its work.