Government scientistscontinue to study the bodies of the aliens whose spacecraft crashedin Roswell, NM in 1947. Among other things, the scientists have investigated the structure of the genetic material isolated fromthe aliens’ cells. This material is similar in some ways toDNA in its chemical makeup. It contains in abundance the 4-carbonsugar erythrose and a molar equivalent of phosphate groups.Additionally, it contains six nitrogenous bases: adenine (A),guanine (G), cytosine (C), uracil (U), inosine (I), and2-thiouracil (S2U).These bases exist in the following proportions:

(C + U +S2U) = (A + G +I)

U = G S2U = A C = I

X-ray diffraction studieshave established a regularity to the molecule and a constantdiameter of

about 23Å.
a. Based on the data described above, propose ageneral structural model for this molecule. Describe itbriefly.

b. What base-pairingproperties must exist for each of the bases in thismodel?

c. Is 2-thiouracil apurine or a pyrimidine?

d. Is inosine a purine or apyrimidine?