DNA is a double helix.

The Watson and Crick model of a double helix structure provides an answer to the 
regularity of the composition in bases and its physiological properties 
(replication in the cell). It is confirmed by diffraction data. 
Models using beads are useful to handle the concept.

The base composition is variable, but in all cases the amount of adenine is 
equal to the amount of thymine (A=T). In the same manner, C=G. 
Consequently A+C=T+G.



D 
Deoxyribo: the pentose does not have any oxygen in position 2. Compare a deoxyribose 
with a ribose. 

N 
Nucleic: these molecules were first found in the nucleus of the cell, before being 
found in mitochondria, chloroplasts (of plant cells), and in the cytoplasm of prokaryotes. 

A 
Acid: only two of the three acid groups of the phosphoric acid are used to form the 
DNA chain. The third one gives the phosphoribo-backbone an acidic property.