Photograph courtesy of The Dolan DNA Learning Center

Three-dimensional models have performed a pivotal role in the development of molecular biology since its origins in the 1950s, both as an experimental technique and in raising public awareness and political and financial support for the discipline. Perhaps the best-known molecular model is Watson and Crick's double helix in the photographs by Antony C. Barrington-Brown.

In the 1980s physical models were replaced in research laboratories by computer-generated images. Although stereo pairs of full-colour images remain popular, some viewers find these hard to see (the observer usually has to go 'cross-eyed'). Alternative methods require the use of expensive polarising filters or LCD-shuttered spectacles. The method described here combines the accuracy of computer modelling with the ease of viewing anaglyph images.

It is relatively simple to create 3-D images from molecular model data and apart from the tinted glasses this requires no camera or special equipment. Molecular modelling software such as RASMOL is available free-of-charge and is well-known in schools...

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This model took John about 3 months (in his spare time) to devise. After salvaging his children's Lego from the attic, John was forced to contact the experts at Legoland. Unlike other Lego DNA models we've seen, this one is relatively accurate with approximately the correct proportions. A giant version of John's Lego DNA model was built at the Experimentarium in Denmark in November 2003.

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This cut-out 3-D model of DNA can be used by students to learn about the structure of DNA. It will take the average person about 90 minutes to assemble a model of 16 nucleotide units. However this activity is better-suited to an entire class, where each student can assemble one base-pair. If the nucleotide pairs are photocopied onto overhead transparency sheets instead of card, these can be assembled to make a particularly attractive model.

The model upon which this one is based was brought to the our attention by Dr Cheong Kam Khow of the Singapore Science Centre. The original was devised by the late Van R. Potter of the University of Wisconsin-Madison in 1958.

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This is a beautiful model from the British family firm of Spiring's, that produces the well-known 'Molymod' range. Unlike the usual Molymod models, it's made of specially-shaped, brilliantly-coloured plastic pieces and is very easy to assemble (I did it without referring to the instructions). The 12 base-pair model is about 23 cm tall and it looks stunning. Everyone in the NCBE office thought it was the best model they'd ever seen and wanted one to decorate their desks. The 24 bp model (45 cm high) is even better.

The revised (2006) version of the model, unlike most introductory DNA models, shows the major and minor grooves in the helix and indicates whether there are two or three hydrogen bonds between each base pair.

There are also pieces available for constructing RNA strands alongside the DNA - you can 'unzip' the model by removing the central supporting spine and pulling the helix apart along the hydrogen bonds. Clearly a lot of thought has gone into this product - every base is a subtly-different shape and they've even made the sugars out of a slightly different plastic so that the model flexes correctly to create a double helix. Plus, you can tell it's British; the phosphate groups are purple, not yellow.

There are also add-on RNA and amino acid parts availablel which can be used to demonstrate protein synthesis.

This tiny model is amazing simply because of the way it has been produced. Data from the Protein Data Bank (.pdb files) are used directly by the Wilwaukee School of Engineering to create exquisite models using sophisticated tools that are usually coupled with CAD-CAM software. They can make virtually any model for which a .pdb file is available, including complex proteins. The Web site is worth looking at simply to marvel at the beautiful models that are on display. Be warned that these models can be very costly; each one is a bespoke job.

This 2-dimensional jigsaw was used by students to learn about the structure, replication and transcription of DNA. The 180 component parts, which were made of robust, coloured plastic, are reversible, provided both a simple and an 'advanced' model (the simple version is shown above on the left; the more advanced one on the right).

The kit comprised sufficient parts for use by a whole class and came with a comprehensive 28-page guide with instructions for teachers and students (available in English, German and Dutch). The pieces and guide were designed to be used at two levels, using either representative letters or complete molecular structures. The DNA jigsaw is no longer available.

Fancy your own Watson and Crick model? This reconstruction of the 'original' model was built for the Dolan DNA Learning Center at Cold Spring Harbor Laboratory in the USA. A team from the Science Museum in London undertook the task. The word 'original' has to be used with caution as Francis Crick has stated that several models were built before the one in the now-famous photographs taken by A. C. Barrington-Brown in May 1953.

The 'original' DNA model was moved from the Cavendish Laboratory to the model room of the MRC Laboratory of Molecular Biology. When, however, the importance of the discovery began to be recognised in the 1970s, the remaining plates were probably taken as souvenirs. A replica model built by Claudio Villa of the LMB for the BBC's 1987 'Life Story' (American title: 'The Race for the Double Helix') also suffered the same fate.

Although there are several who claim to have some of the metal plates from which Watson and Crick's DNA model was constructed, the truth is hard to discern. Some plates appear to have been sent, in error, to a scientist who left the LMB to take up a post at Bristol University, and these were used in the reconstruction found in the Science Museum. All of today's reconstructions are based on Barrington-Brown's photos.

Photograph courtesy of The Dolan DNA Learning Center

The CHIME plug-in can be used to view molecular structures within older versions of the Netscape Web browser.

The frame shown on the right comes from a complete suite of animated, interactive CHIME pages designed to help students learn about the structure of DNA.

It can be viewed or downloaded entirely (for viewing off-line) from: http://molvis.sdsc.edu/dna/index.htm

This is a colourful, robust classroom model which, once assembled, can't be taken apart. It stands about 22 cm tall when completely compressed, and 85 cm tall when extended to the fullest extent. At full stretch, it looks simply like a ladder, which is useful for demonstrating the structure of DNA at a very basic level.

It comes with a small (8-page) instruction booklet that includes information about DNA's structure that can be used when teaching.

We found it very difficult to extend and hold the model to obtain the correct 10 base-pairs per turn - the photo on the right shows it pulled up the maximum extent at which it will remain self-standing. Pull it any further and it'll spring out into the 'ladder' formation.

As a model it tells you little more than could easily be shown in a quickly-sketched diagram, but it might be useful if you need to demonstrate just the essential elements of the structure.

In our opinion, this is the worst 'DNA' model we've ever encountered. We found it difficult to make and if you follow the instructions you'll have a left-handed double helix with six base-pairs per turn instead of the ten you'd expect. Oddly, all the photos on the accompanying leaflet show a right-handed double helix. To us, the leaflet was bewildering nonsense ("Meet Felix, the Double Helix" is about as eloquent as it gets), but at least the manufacturers have the honesty to admit that "Zome DNA model is a simplified approximation of the actual DNA molecule". Quite.

The photo on the right does not do justice to this accurate scale model. It's a DIY model that is really intended for the connoisseur. In fact, we haven't finished building it yet (you can see that the lower part lacks sugar-phosphate backbones). The plastic parts clip together and are strong, but the model would not stand up to rough handling in the classroom. It would, however, make a fine display model. There are no paints provided but the detailed booklet with this kit explains how to colour-code each atom. The completed model stands on an attractive and sturdy wooden base. The model is about 60 cm tall and roughly 15 cm in diameter. The accompanying booklet includes numerous questions for students encouraging them to analyse the structure in detail.

Danish origami expert Thoki Yen's ingenious model of DNA is simple to make, and can be extended to provide additional turns (although it can be tricky to fold a long strip of paper accurately, and you may have to resort to sticking several models together). You can download the instructions from Thoki's Web site; they were also published in Trends in Biochemical Sciences, Volume 20, page 94.

This large (2.5 m) Molymod DNA model was made by Graeme Jones from Keele University, as part of the 'DNA 50' celebrations organised by the British Council.

It's now in the laboratory of the excellent Science Festival School at the International Institute of Cell and Molecular Biology in Warsaw.

In 2002, Graeme had been involved in building the world's biggest DNA model, a 12-metre high version of this Molymod construction.

This inexpensive, 12 bp model stands about 45 cm high. It is easy to build and shows the general structural features of DNA plus the transcription of 4 bp to mRNA. It's made from tough plastic straws and linking units.

Although sufficient base-pairs are provided to show one complete turn of the double helix, the supporting rod is not tall enough to allow this. The grey and green straws are similar in colour and can therefore be confused in poor light (I made the model wrongly on my first attempt). It would also be a good idea to provide linking units that represent ribose in a different colour to those of deoxyribose.

Cochranes also manufacture another, larger model which shows every atom and bond in a 15 bp length of DNA.

Usefully, spare parts are also available.

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