Shown below is an R loop prepared for electron microscopy by annealing a purified eukaryotic messenger RNA with DNA from a genomic clone containing the full-length gene corresponding to the mRNA.

(a) How many exons does the gene contain? How many introns?
(b) Where in this structure would you expect to find a 5€², 5€²-internucleotide bond? Where would you expect to find a polyadenylic acid sequence?