Micscape Lite - Product Review

DNA Molecular Model Kits compared and contrasted - helices and two base pairs.

by David Walker, UK

Maker - unbranded Source - e.g. eBay UK Price - typical £4-30 with shipping Height - 34 cm

Despite its price, this simple and cheap model made of plastic and card (model immediate right) shows some key features well; the double helix, the G-C and A-T base pairing. Also ideal for showing right handedness and can be assembled in the left handed form to show they are not equivalent. It does not show the major and minor ridges nor features at the molecular level. It is the easiest of those reviewed to show the 36° twist for each base pair by holding a protractor on the axis. It is robust with some care in handling. Can be disassembled for storage. The model could be part built, helix split and pairs cut apart to show some basic replication concepts. Some similar kits e.g. offered on Amazon have clear not coloured plastic strip backbones.

Suggested complementary model: A smaller two base pair model illustrated below to show molecular structure of the base pairs and sugar-phosphate backbone.

The pre-cut base pairs are made of stiff foam with card facings, the backbones are pre-notched plastic strips.
The spacers nest to form the stand.

Maker - Molymod www.molymod.com Model - Advanced miniDNA AMDNA-06-22 for 22 base pairs Source - e.g Amazon and edu' suppliers Price - typical £39-12 (inc. VAT).
Height - 47 cm Scale - ca. 1 cm = 2 Å.

The 22 base pair model was tried (image above far right), there is also a 12-layer model. The model from this well established British maker shows a number of additional key features to the simpler helix above. It is one of the clearest of those reviewed to show the major and minor grooves, more clearly perhaps than the Minit kit built to the atomic level as there are 22 rather than 15 base pairs. Some indication of the helical backbone structure is shown from the purple tetrahedral phosphate groups and the pentagonal sugars. The base pairs have double and triple bonded hydrogen bonds but the bases are arbitrary shapes not reflecting their molecular structure. Labelling them after purchase as standard with the DynamicDNA kit below could be useful.

The kit as with all Molymod kits are presented well and supplied instruction leaflet is clear which illustrates how it can be used to demonstrate replication.

Suggested complementary model: The molecular structures of the base pairs can be illustrated by building the Molymod 'open model kit' article number MKO-ACGT-53 using the standard Molymod atomic system. See below.

Maker - Cochranes of Oxford www.cochranes.co.uk Model Minit ProView DNA Model Kit with 15 base pairs Source - direct from Cochranes and edu' suppliers
Price - £123-20 (£147-84 inc. VAT) Height x Width - 127 x 41 cm Scale - 1Å = 2 cm

This kit has been reviewed in detail in the April 2021 issue of Micscape where assembly tips were also suggested. It is built using the maker's well established Minit system. To speed the assembly, it could be readily split into modules for a class of students (it took the author a week assigning a few hours or so a day to the build). This is the finest way of really understanding the DNA structure; the base structures and hydrogen bond pairing, anti-parallel phosphate - sugar backbone. When built and assembled it provides a great deal of satisfaction! The string suspension system with key atoms already attached to the strings greatly eases the potentially tricky step of adding the backbones.

This is arguably best as a build once model for permanent display, the bonds loosen on reuse. On a low ceiling (as in the author's home) it occupies little room. It maybe more vulnerable in a classroom environment, the suspension system is stable but potentially vulnerable to knocks. A free standing support with storage in a side room may be one approach for safe keeping. As remarked in the intro', even a photo of a 3D model flattens the structure emphasising why hands on is so beneficial.

Cochranes also sell the kit in the larger scale Orbit system (a two base pair shown in later table). This is larger but does have a custom stand available. See the maker's website for an image of an assembled model for scale.

Maker - ChemKits www.chemkits.com Source - maker's website Model - Organic Chemistry kits - Price - $41-99 Scale - ca. 1 inch = 1Å

This model system uses metal atom centres with coloured bonds. It also shows the Van der Waal's distances of hydrogens. A clear, open structure is achieved for this DNA model although perhaps the VDW's bond extensions may confuse the basic structure somewhat but could be snipped off. The vertical bond prongs can be used to make supports for the structure but remains quite fragile if handled. Two kits may be needed to complete as the author has multiple kits (my first acquired in a chemistry course in the 70s, the system has a long pedigree). The separate base pair groups are quite robust for handling.

Maker - 3D Molecular Designs www.3dmoleculardesigns.com Source - maker's website, TimStar in UK Model - DynamicDNA Price - two, six and 12 base pairs: $45, $124, $237 Height - Scale - ca. 1 in 80 million stated

As the name suggests this is a dynamic model that uses an innovative combination of magnetic bonding and keyed connectors to form a model that in its 6 or 12 base pair form can be untwisted and used to illustrate replication and transcription. Of those base models built it is the most robust, maintains the base pair spacing and can be readily handled between students. The author has the two base pair kit shown below but the 12 base pair is illustrated below courtesy of the makers.

Left above: The two base pair kit built by the author.
Right above: The 12 base pair kit which includes a stand for vertical display. Photo courtesy of 3D Molecular Designs, LLC. The Dynamic DNA Kit^© is manufactured by 3D Molecular Designs, in Milwaukee Wisconsin, US. It is available in the UK from Timstar Laboratory Suppliers https://timstar.com/mo190100-dynamic-dna-kit.html

Above. The molecular structures of base pairs, sugars and phosphates are shown with atoms colour coded. Labels are provided. The correct base pairs attract via the magnets to make the bonds. 3DMolecular Designs offer invaluable, detailed Teacher's Resources describing the more extensive capabilities of the system to show replication and transcription.

Maker - Molecular Visions (Darling Models) www.molecularvisions.com Model /price A-T #13a and G-C #13b $4 each, sugar-phosphate #13c $2-25  Scale - 1Å = 2 inches.

This system uses coloured atom - bond integral units with atom centres built from interlocking units. This system of those tested requires the most pre-assembly familiarity with how the system works; the ball and stick systems are more intuitive. Care needs to be taken to ensure prongs and receptors of the bond connectors are in the correct places for assembly. The instruction sheet notes these but the coloured expanded view of the completed units in the extensive booklet provided with the general kits was found more useful.

Base pair kits for G-C and A-T are available in this system and sugar, phosphate groups. The large scale of this system makes them ideal for demonstrations with the coloured bonds rather than atoms easier to see at distance. This kit by default shows the double bonds in the bases; this is possible with the other systems but less routine for complex molecules. However, its scale and bond flexibility makes this system the most unsuitable for showing as a part helix of the two base pairs of the systems tried, not helped by the free rotation of the sugar and phosphate bonds in the backbones. Building a two base pair model and devising a means to support it for a photo' was challenging using materials to hand with a cluttered result; a retort stand, coat hanger wire, cable ties, Plasticine and some computer stand base supports was the best could do!

Maker - Molymod www.molymod.com Model MKO-ACGT-53  two separate base pairs, MKS-122-10 ten base pairs with stand Source - edu' suppliers two pairs, typically £19-89 exc. VAT, ten pairs £142 plus VAT. Amazon US currently stocks the 10 base pairs $230.  Price - Scale - 'open / ball and stick' 1Å = 2.5 cm, 'closed / semi-space filling' 1Å = 1.5 cm

This system can be built using either short bonds to give a semi-space filling model or with longer bonds to approach a more ball and stick type. The MKO-ACGT-53 kit allows the separate two base pairs G-C and A-T to be built in open form. The various organic / biochemistry kits in the system can be used to build the backbones. The shorter bonds are more rigid and thus preferred for a two base pair part helix. Some support as shown was required for the planes not to sag and to provide some support to the backbones. To hand around the separate base pairs both bond types are suited and quite robust. The longer bonds allow the double bonds to be shown using an sp³ atom in an sp² role. Strained atom angles are not available so the shorter bonds are strained and tend to ping out in the five membered rings even with the special flexible 'V-link' ML-20 bonds. The large coloured atoms give a clear indication of molecular structure.

A splendid ten base pair model MKS-122-10 with the shorter bonds is available with stand that provides the base pair support.

Model using the shorter bonds to give a 'closed / semi-space' filling model.

Base pairs using the longer bonds to give an 'open / ball and stick' model.

Maker - Cochranes of Oxford www.cochranes.co.uk Model Orbit ProView DNA model Kit with 15 base pairs Source - direct from Cochranes and edu' suppliers Scale - ca. 1Å = 3 cm
Price - Full 15 base pair DNA kit £130-40 (£156-48 inc. VAT). Two base pairs can use the Biochemistry Class kits £52-77 (£63-32 inc. VAT).

Like the Minit, it is a 'ball and stick' type with coloured atoms but at a larger scale. Two base pairs could be built using the Biochemistry Class kit. The molecular structure of the base pairs and sugar-phosphate backbone is clearly shown at this larger scale. The holes in the atoms are useful for supporting the two layers the correct distance apart. It is a rather delicate structure though for handling. The separate two base pairs are robust for handling and can be separately presented and stored. Both the Orbit and Minit systems provide carbon and nitrogen atoms of the correct angles for strained rings and each are marked.