ABSTRACT
DNA, the genetic material common to all life forms, has the inherent property of self-adhesion. The famous double helix consists of two strands of DNA that adhere to each other because of the attractive forces of hydrogen bonds that occur between DNA’s four chemical residues: the bases A, T, C, and G. This adhesion occurs in a very specific manner such that the A bases bind to T’s and the C’s to G’s (Fig. 16.1). Stretches of sequence bind only to complementary stretches that have a high percentage of the bases matching up correctly. For example, the sequence ATTCGAGTTA will bind more tightly to its exact complement, TAAGCTCAAT (where every A aligns with a T and every C with a G), than it will bind to TAACCTCATT, which has only 8 out of 10 bases lining up with its complement. Geneticists and molecular biologists have been taking advantage of the nature of one strand to bind (or hybridize) to another strand and especially how the strength of this binding is related to the number of bases that are complementary. For decades researchers have been analyzing nucleic acids (DNA and RNA) that have been size separated through gel matrixes, as in the use of Southern blots (1) to analyze gene structure/ organization, and in the use of northern blots (1) to examine gene expression (mRNA abundance). In these techniques, single-stranded DNA or RNA is stabilized on a membrane and is then hybridized with radioactively labeled nucleic acid to identify or quantify fragments of interest.
