Answer
Fig. 4.1
The helix would bulge where two purines are paired and be constricted where two pyrimidines join U.
Work Step by Step
Pyrimidines and purine do not pair up arbitrarily in the DNA structure. Usually Adenine and thymine pair up(A-T) and guanine and cytosine join up(G-C).So where there is a an A on one backbone there is a T on the other backbone facing it (the A-T base pair), and C and G also form a base pair.
