Structure of Nucleic Acid The nucleotides are made of phosphate, a pentose sugar, nitrogenous base. DNA is measured by the number of base pairs it has. Structure of Prokaryotic Genomes. The genome is composed of a single double-stranded DNA molecule in the form of a loop or circle. Contain single circular chromosomes 0.6-10Mb in length and circular plasmid species of 2kb-1.7Mb. Structure of Eukaryotes Genomes Have larger and more complex than those of prokaryotes. Eukaryotes cells are often diploid (two chromes copies?). Chromosomes are linear and within the nucleus.