Hennann Dugas University of Montreal
Montreal, Quebec Canada H3C3V1
I
A simplified Molecular Model of t-RNA for Use as a Teaching Aid
In recent years, considerable interest and work have been focussed on the three-dimensional structure of t-RNA molecules. Since it is often difficult to convey ideas concerning the relationships which exist between the structure and the function of a biological molecule, it was decided that the construction of a simple molecular model of class I t-RNA (with small variable loop) would be useful for both chemistry and biochemistry students. I believe that such a model can assist the teacher in illustrating secondary and tertiary interactions in biomolecules and thus can help familiarize the students with the idea of base pairing and base stacking encountered in nucleic acids. This paper described an easyto-build. inexnensive. model which can be assembled within one afternoon in the laboratory. Figure 1. Photograph of the molecular model using the sequence of E. cob tFieure 1 shows a ohotoma~hof the molecular model fur E. RNAm. coli L R N A P ~~~h.e m O d i w built k using the X-ray results's2 obtained from yeast t -RNAPhe. Basically, our model consists of a 1.5-mm aluminum (galvanized) rod of about 1.3 m lone and small olastic olates (about 40) madeof a 1.5-mm t h i ~ ~ ~ o l ~ ~shee; r o as~ il~ l e ~ e lustrated in Fieure 2. The aluminum rod is used to construct the backbone i f the molecule end the plates represent the Watson-Crick base pairs. A cardboard roll (4.3 cm in diameter) can be used to twist the aluminum rod into helical regions. The plates are narrow enough so as not to over-crowd the model. Incisions are made at both ends of the plates so that they can snap on easily to the metallic frame. For non-hydrogenbonded nucleotides, the plates are simply cut in half. Each nucleotide can be identified on the plate using a press-on letter Figure 2. Dimensions of lhe polypropylene plates (actualsize). set and the plate is transparent enough so as to see the letter when the model is turned or when it is up-side down. If neca different t-RNA, (2) the location and orientation of Watessary, the non-hydrogen-bonded plates can be fixed person-Crick base pairs as well as base stacking are easily demmanently to the rod, in the proper orientation, with a drop of onstrated, (3) the importance of extra hydrogen-bonded inepoxy glue. teractions for the maintenance of the tertiary structure of the The plates involved in extra (tertiary) hydrogen-hondings (10 of them) are colored on the edee with aoen marker for easv molecule becomes apparent, (4) the continuous double helix identification. A perforated s m k plasticball (0.7 cm in dLmade of T+C and acceptor stems is easily seen, and finally, (5) the change in conformation which takes place upon aminoaameter) and a lareer one (1.5 cm in diameter) can be added to the 5-ft end ana 3-ft end to represent, respectively, the cylation can be i l l u ~ t r a t e d . ~ phosphate group and the corresponding amino acid. In conclusion, the molecular model is judged to possess The size of the model was found to be convenient even for several advantages. I t is quickly and easily assembled from large lecture rooms and can be carried in a shoe box. The diinexpensive and readily available materials. I t is also applimensions of the model correspond to a scale of 1cm F.: 3.5A. cable to other nucleic acid molecules. For example, the distances between the 3-ft end and anticodon We wish to thank Mr. A. Combey, from our mechanical shop, for cutting and perforating the plastic plates. loop, the 3-ft end and 5-ft end, and the 3-ft end and T$C Imp are, respectively, 22 cm (77A), 8 cm (28A), and 18 cm (63&, values comparable to those found hy X-ray crystallogra'Kim, S. H.,Quigley, G. J., Suddath, F. L.,McPherson,A,, Sneden, phy. D., Kim, J. J., Weinzierl, J.,and Rich, A,, Science, 179,285 (1973). 11 is possible to demonstrate to studenta several important 2Sussman,J. L., and Kim, S. H.,Biochem. Biophys. Res. Commun., advantages which are inherent in this molecular cunstmction: 68.89 (1976). (1) the dates can be removed a t will by unsnapping them from Taron, M., Brisson, N., and Dugas, H., J. Bid. Chem., 251,1529 the metallic frame and can be replaced by others to construct (1976).
298 / Jwml of ChemicalEduc~tion
