 DNA normally exists as a double @-@ stranded molecule , coiled into the shape of a double helix . Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand : A pairs with T , and C pairs with G. Thus , in its two @-@ stranded form , each strand effectively contains all necessary information , redundant with its partner strand . This structure of DNA is the physical basis for inheritance : DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand . 
