Nucleic acids
DNA and RNA are nucleotide polymers. DNA usually contains deoxyribose and thymine; RNA contains ribose and uracil. Phosphodiester linkages connect adjacent nucleotides in a strand. The two strands in a typical DNA double helix run antiparallel: one 5′ to 3′ and the other 3′ to 5′. A pairs with T in DNA and with U in RNA; G pairs with C. The order of bases stores information. Heating can separate DNA strands by disrupting interactions between bases without necessarily breaking the sugar–phosphate backbone.
For a double-stranded DNA sample with 28% adenine, thymine is also 28%. The remaining 44% is split equally between guanine and cytosine, giving 22% each.
Complementary base pairing does not mean every RNA has equal A and U percentages. That equality is guaranteed for an entire fully paired double-stranded molecule, not an arbitrary single strand.