Complementary polydeoxynucleotide

The first evidence of the special structure of DNA was the observation that the amounts of adenine and thymine are almost equal in every type of DNA. The same applies to guanine and cytosine. The model of DNA structure formulated in 1953 explains these constant base ratios intact DNA consists of two polydeoxynucleotide molecules ( strands ). Each base in one strand is linked to a complementary base in the other strand by H-bonds. Adenine is complementary to thymine, and guanine is complementary to cytosine. One purine base and one pyrimidine base are thus involved in each base pair. 

DNA in the chromosomes of most organisms is double-helical-, i.e., it consists of two polydeoxynucleotide chains (or strands) twisted around one another in the form of a helix. The genetic information is contained in the sequence of nucleotides along one of the chains, with the sequence in one being complementary to that in the other (Chap. 7). A replica of DNA is one that is an exact copy of itself. 

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