DNA Replication

DNA, an abbreviation for deoxyribonucleic acid, is a double-stranded, helical molecule (visually, it resembles a ladder that is twisted into a spiral staircase shape) that forms the molecular basis for heredity. For the manufacture of a new double helix of DNA to occur in the process of DNA replication, this molecule must first unwind itself to allow the information-encoding building blocks of the DNA (the bases) to become accessible.

The base pairing within DNA is specific; the base called adenine pairs with the base called thymine, and the base cytosine pairs only with the base called gua-nine. Put another way, the pairing is complementary. When a stretch of the DNA double helix separates into the two strands of bases due to the action of enzymes, each of the exposed strands acts as a template for the formation of a new strand that contains the complimentary sequence of bases. The process, which involves the coordinated activity of several different enzymes, produces two completely new and identical daughter strands of DNA.

This method of replication is known as the semi-conservative model. A competing hypothesis, which was eventually disproved, was the conservative hypothesis; it predicted that separating of the strands of the double helix was unnecessary, and that two new strands could form along side the existing strands even when they were linked together. Experiments conducted by Matthew Meselson and Franklin W. Stahl in the late 1950s that traced the incorporation of radioactive compounds into the newly forming DNA established beyond all doubt that the conservative model was incorrect.