a model for representing nucleic acid molecules , such as deoxyribonucleic acid and ribonucleic acid consists of a plurality of helical segments secured together in end to end relation in the form of one or two helixes comprising the molecular backbone . each of the helical segments is proportioned in length and helical curvature to be a model of the backbone units of the dna and rna molecules . each unit has a flat planar member extending from the mid portion thereof which has a shape corresponding to one of the bases found in each of the separate nucleotides . means are provided for securing the bases on opposing nucleotides together to hold a pair of helical molecular backbones together , with the helical segments and planar members illustrating the size , proportions , and relationship in the molecule in the various nucleotides .