Chapter 11 Textbook Gentics

In 1958, Meselson and Stahl resolved the question of which of three potential modes of replication is utilized by E. coli during the duplication of DNA in favor of semiconservative replication, showing that newly synthesized DNA consists of one old strand and one new strand.

Taylor, Woods, and Hughes demonstrated semiconservative replication in eukaryotes using the root tips of the broad bean as the source of dividing cells.

Arthur Kornberg isolated the enzyme DNA polymerase I from E. coli and showed that it is capable of directing in vitro DNA synthesis, provided that a template and precursor nucleoside triphosphates are supplied.

The discovery of the polA1 mutant strain of E. coli, capable of DNA replication despite its lack of polymerase I activity, cast doubt on the enzyme’s hypothesized in vivo replicative function. Polymerase III has been identified as the enzyme responsible for DNA replication in vivo.

During the initiation of DNA synthesis, the double helix unwinds, forming a replication fork at which synthesis begins. Proteins stabilize the unwound helix and assist in relaxing the coiling tension created ahead of the replication fork.

DNA synthesis is initiated at specific sites along each template strand by the enzyme primase, resulting in short segments of RNA that provide suitable ends upon which DNA polymerase III can begin polymerization.

Concurrent DNA synthesis occurs continuously on the leading strand and discontinuously on the opposite lagging strand, resul