If the figure on page 34 of your article on the structure of DNA is an accurate representation of bonding between base pairs, then the alternative DNA structure proposed by Mark Curtis cannot be correct ("Deconstructing DNA", 16 May, p 32).
Under the classic Watson and Crick scheme, three hydrogen bonds link cytosine and guanine, whereas adenine and thymine are linked by only two. This bonding pattern is supported by the observation reported in many elementary biochemistry texts that it takes more heat energy to separate strands of DNA rich in C-G than for DNA in which A-T base pairs predominate, partly because C-G pairs are held together more strongly by their three bonds than A-T pairs are by two.
According to Curtis's new structure, however, both base pairings appear to be linked by only two bonds. A double helix held together by such bonds would not exhibit the ...
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