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. DNA mechanism is process is known as semi-conservative replication because two copies of the original molecules are produced.