When the strands of the probe are separated, they will be able to bind to complementary sequences, either the original binding partners or the same sequences found in any other DNA molecules whose source interests us. Using procedures that locate the label on the probe, we can detect those specific sequences in the DNA sample of interest. This capability is at the heart of all DNA diagnostic methods. The sugar in RNA is ribose, not deoxyribose. This is important because the 2' hydroxyl can act as a nucleophile to catalyze the hydrolysis of the phosphodiester bond involving the adjacent 3' hydroxyl, especially if the hydrogen ion is removed, making RNA is inherently less stable than DNA, especially at high pH. 2.
Uracil replaces thymine.
Naturally occurring RNA is usually single-stranded. Within the single strands, short base-paired regions can be formed by folding the chain back on itself. Single stranded nucleic acid molecules have fewer structural constraints, and are able to form a wider variety of base-base contacts since they can tolerate more conformations. This is true of both DNA and RNA, but is more common with RNA since it is more often found in a single-stranded form. RNA bases are often chemically modified after formation of the RNA strands.