. Biophysical science. Biophysics. 294 X-ray Analyses of Proteins and Nucleic Acids /15 : 6. C P O o O H Base pairs with about 10 rungs per turn. The pairs of bases fit across the chain as rungs being supported in the middle by hydrogen bonds. It is necessary that each pair of bases fit very exactly. Measurements based on X-ray diffrac- tion patterns of crystals of the purine and pyrimidine bases have shown that these do indeed fit, provided that adenine (A) is paired with thymine (T), and guanine (G) with cytosine (C). If this is the case, one should have the relative concentrations of organi
. Biophysical science. Biophysics. 294 X-ray Analyses of Proteins and Nucleic Acids /15 : 6. C P O o O H Base pairs with about 10 rungs per turn. The pairs of bases fit across the chain as rungs being supported in the middle by hydrogen bonds. It is necessary that each pair of bases fit very exactly. Measurements based on X-ray diffrac- tion patterns of crystals of the purine and pyrimidine bases have shown that these do indeed fit, provided that adenine (A) is paired with thymine (T), and guanine (G) with cytosine (C). If this is the case, one should have the relative concentrations of organic bases in DNA related as [A]/[T] = [G]/[C] = This relationship had been verified for all DNA and was one of the pieces of evidence used by Crick and Watson to construct their model. Gamow tried to explain protein for- mation in terms of the location of residues along the DNA chain. The diagram in Figure 14 shows the type of blocks Gamow considered to deter- mine amino acid arrangement. In the outlined cross, G, T, and C are in- dependent, but the A is determined by Figure 13. The helix of DNA, with three different ways of representing the molecular arrangement. Top, general picture of the double helix, with the phosphate-sugar com- binations making up the outside spirals and the base pairs the cross-bars; middle, a some- what more detailed representations: phos- phate (P), sugar (S), adenine (A), thymine (T), guanine (G), cytosine (C), and hydrogen (H); bottom, detailed structure showing how the space is filled with atoms: carbon (C), oxygen (O), hydrogen (H), phosphorus (P) and the base pairs. After C. P. Swanson, The Cell, (Englewood Cliffs, N. J.: Prentice- Hall, Inc., 1960).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ackerman, Eugene, 1920-. Englewood Cliffs, N. J. , Prentice-Hall
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