This demonstration model reproduces the structure of the deoxyribonucleic acid (DNA) molecule and the principle of complementarity of the nitrogenous bases. It is used in institutions of general secondary and higher education in lessons of biology, genetics and molecular biology when working through the topic “Structure of DNA”, and work with it gives pupils the opportunity to assemble a fragment of the molecule step by step, to study the mutual arrangement of its components and to grasp the principle of self-duplication of hereditary material. The model is used under the supervision of a teacher, and pupils of the junior grades work with it under the direct care of an adult; the recommended age of learners is from 10 years, that is pupils of grade 5 and above.
The total height of the model when assembled is 90 cm. It is composed of coloured elements — the nitrogenous bases, the residues of phosphoric acid, the deoxyribose and the central axis — which connect to one another, and the elements are made of high-quality and safe materials, namely polysulfone, an impact-resistant plastic. Each element has its own colour designation for easy recognition, and the colour marking follows the internationally accepted standard: adenine is light green, thymine yellow, cytosine orange, guanine blue, phosphoric acid white, deoxyribose red and the central axis white. The model has a full axis of rotation and turns around the central axis, which allows the double helix to be examined from all sides; the dimensions of the slots are clearly reproduced and provide an exact connection of the components, and the sizes of the separate elements are optimised for demonstration and for work in the hands. The number of nitrogenous base pairs in the fragment depends on the composition of the set, and the model needs no power supply.
The set includes the nitrogenous bases, that is adenine, thymine, cytosine and guanine, according to the list in the packing list, the residues of phosphoric acid as white elements according to the packing list, the deoxyribose, a pentose, as red elements according to the packing list, the central axis for rotation of the model — 1 pc, hydrogen bonds according to the configuration, the passport with the warranty coupon — 1 pc, and individual transport packaging — 1 pc. Diagrams with captions of the main elements are supplied with the set and help pupils to identify the components correctly and to understand the molecular structure of DNA. The model is delivered disassembled and ready for assembly, and the elements are packed so as to prevent the loss of small parts during transport.
The elements are laid out on the demonstration table of the biology room so that they are visible to the whole class, sorted by colour into separate groups. Assembly begins with the central axis, after which the residues of phosphoric acid, then the deoxyribose and then the nitrogenous bases are installed level by level, observing the principle of complementarity, in which adenine always pairs with thymine and cytosine with guanine; each element enters its socket tightly but without excessive force, and if an element does not enter easily its orientation is checked first. The assembled model is rotated slowly around the central axis and only around it; the helix is not bent and the model is not divided into arbitrary parts. The set contains small parts that are dangerous for children under three years of age, so it is kept out of the reach of young children and is not left unattended. The elements are wiped with a soft dry cloth, and when soiled with a slightly moistened soft cloth followed by wiping dry, while abrasive materials, alcohol, acetone and aggressive chemical agents are excluded; the elements are dried naturally at room temperature. The operating conditions are the premises of an educational institution at an air temperature from +5 to +40 °C and relative humidity from 40 to 60 % without condensate, out of direct sunlight and away from sources of heat. Marking and operating documentation are in Ukrainian, and the marking carries the trade mark, the model and a place for the inventory number. The service life is 5 years and the warranty period is 12 months from the date of sale.
