Essentials of Genetics 9th Edition by Michael Palladino William Klug, Michael Cummings, Charlotte Spencer

Exercise 6

Reconsider Problem 1 in Chapter. In the model you proposed, could the molecule be replicated semiconservatively? Why? Would other modes of replication work?
Problem 1
Newsdate: March 1, 2015. A unique creature has been discovered during exploration of outer space. Recently, its genetic material has been isolated and analyzed, and has been found to be similar in some ways to DNA in chemical makeup. It contains in abundance the 4-carbon sugar erythrose and a molar equivalent of phosphate groups. In addition, it contains six nitrogenous bases: adenine (A), guanine (G), thymine (T), cytosine (C), hypoxanthine (H), and xanthine (X). These bases exist in the following relative proportion:

X-ray diffraction studies have established a regularity in the molecule and a constant diameter of about 30 Å.
Together, these data have suggested a model for the structure of this molecule. (a) Propose a general model of this molecule, and briefly describe it. (b) What base-pairing properties must exist for H and for X in the model? (c) Given the constant diameter of 30 Å, do you think either (i) both H and X are purines or both pyrimidines, or (ii) one is a purine and one is a pyrimidine?