DNA replication

Meselson–Stahl Experiment

In their second paper on the structure of DNA*, Watson and Crick (pdf) described how DNA's structure suggests a pattern for replication:

"…prior to duplication the hydrogen bonds are broken, and the two chains unwind and separate. Each chain then acts as a template for the formation onto itself of a new companion chain, so that eventually we shall have two pairs of chains, where we only had one before." - Watson and Crick, 1953

This is called semiconservative replication.

Today we know that this is the pattern used by living cells, but the experimental evidence in support of semiconservative replication was not published until 1958. In the 5 years between Watson and Crick's suggestion and the definitive experiment, semiconservative replication was controversial and other patterns were considered.

DNA Polymerase

DNA polymerases are the enzymes that replicate DNA in living cells. They do this by adding individual nucleotides to the 3-prime hydroxl group of a strand of DNA. The process uses a complementary, single strand of DNA as a template.

The energy required to drive the reaction comes from cutting high energy phosphate bonds on the nucleotide-triphosphate's used as the source of the nucleotides needed in the reaction.

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