why dna wound into a double helix
1 The helix in the double helix means that the entire thing is wound up in a spiral. 2  DNA composition: purine and pyrimidine bases, sugars, phosphate. 3  Nucleotide = base (Adenine, Guanine, Thymine, Cytosine) + sugar + phosphate. 4  Nucleoside = base + sugar = Adenosine, Guanosine, Thymidine, Cytidine.