Spirala DNA

Deoxyribonucleic acid, or DNA, consists of two polynucleotide chains.

Each of these chains is made up of four types of nucleotide subunits.

Each nucleotide consists of a single phosphate group and a nitrogen-containing base — adenine, A, cytosine, C, guanine, G, or thymine, T, attached to a sugar deoxyribose.

This arrangement creates the sugar-phosphate backbone of the DNA structure.

Along the backbone of each strand, phosphodiester bonds covalently link the third carbon atom of one sugar to the fifth carbon atom of the next sugar molecule in the chain.

In the opposing antiparallel strands, each base is uniquely paired, C with G and A with T, due to the differences in the number of hydrogen bonds that form between them.

Such chemical polarity ensures efficient packing, winding the two strands around each other to form a 3-D double helix, with ten base pairs every full turn.