What Is a DNA Structure?

By Krista Sheehan

Essentially, DNA is the blueprint for our hereditary and genetic makeup. Found in each cell in the human body, each person's DNA is entirely unique to his genetics. With such an important and critical job, it is surprising that the DNA structure is so simple.


A strand of DNA is composed of two polynucleotide strands wound together into a double helix structure. Each spiral strand is composed of a sugar-phosphate backbone and its attached bases.


The sugar-phosphate backbone consists of a deoxyribose, which is a sugar with five carbons. This sugar is attached to phosphoric acid. The sugar-phosphate backbone is on the outside of the double helix of the DNA.


A variety of bases are attached to the backbone. The bases are adenine, guanine, cytosine and thymine. These bases project into the inside of the double helix and are attached to a specific base on the other strand.

Hydrogen Bonds

A series of hydrogen bonds attach the bases from one strand to the bases on the other strand. Adenine and thymine bases are connected to each other by two hydrogen bonds, while guanine and cytosine are connected to each other by three hydrogen bonds.

Helical Turn

Each pair of bases (one from each strand) is called a nucleotide pair. There are approximately 10 nucleotide pairs per turn of the double helix.