DNA .. the chemical secert

In living organisms, DNA does not usually exist as a single molecule, but instead as a tightly-associated pair of molecules.
These two long strands entwine like vines, in the shape of a double helix.
The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a base, which interacts with the other DNA strand in the helix.
In general, a base linked to a sugar is called a nucleoside and a base linked to a sugar and one or more phosphate groups is called a nucleotide.
If multiple nucleotides are linked together, as in DNA, this polymer is referred to as a polynucleotide.
The backbone of the DNA strand is made from alternating phosphate and sugar residues.[8] The sugar in DNA is 2-deoxyribose, which is a pentose (five carbon) sugar.
The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings.
These asymmetric bonds mean a strand of DNA has a direction.
In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand. This arrangement of DNA strands is called antiparallel.
The asymmetric ends of a strand of DNA bases are referred to as the 5 (five prime) and 3 (three prime) ends. One of the major differences between DNA and RNA is the sugar, with 2-deoxyribose being replaced by the alternative pentose sugar ribose in RNA.
The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T).
These four bases are shown below and are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate.