Hybridization

Hybridization is a technique in which molecules of single-stranded de­oxyribonucleic acid (DNA) or ribonucleic acid (RNA) are bound to com­plementary sequences of either single-stranded DNA or RNA. Complementary base pairs are adenine (A) with thymine (T) or uracil (U) and vice versa, and guanine (G) with cytosine (C) and vice versa. Although the DNA double helix is relatively stable at body temperatures, high tem­peratures can split, or “melt,” the double helix into single, complementary strands. After disrupting the double helix in this way, lowering the temper­ature then causes the single-stranded DNA to base-pair, or anneal, to other single strands that have complementary sequences.

Single-stranded DNA can hydridize to either single-stranded DNA or single-stranded RNA. Two complementary single-stranded DNA molecules can reform the double helix after annealing. In DNA-RNA hybridization, the RNA base uracil pairs with adenine in DNA. Single-stranded RNA that is complementary to a messenger RNA (mRNA) sequence is called “anti­sense” RNA. Antisense RNA and mRNA form a double helix that is slightly different from a DNA double helix.

Researchers use hybridization for many purposes. Overall genetic re­latedness of two species can be determined by hybridizing their DNA. Due to sequence similarity between closely related organisms, higher tempera­tures are required to melt such DNA hybrids when compared to more dis­tantly related organisms. In forensic DNA testing, a variety of different methods use hybridization to pinpoint the origin of a DNA sample, in­cluding the polymerase chain reaction (PCR). PCR produces many copies of a particular nucleic acid sequence and is also used to clone genes. In an­other technique, short DNA sequences are hybridized to cellular mRNAs to identify expressed genes. Pharmaceutical drug companies are exploring the use of antisense RNA to bind to undesired mRNA, preventing the ri­bosome from translating the mRNA into protein.

References

Alberts, Bruce, et al. Molecular Biology of the Cell, 4th ed. New York: Garland Pub­lishing, 2000.

Freifelder, David. Molecular Biology, 2nd ed. Boston: Jones & Bartlett, 1987.