The Meselson - Stahl Experiment

"the most beautiful experiment in biology"

DNA Replication is Semiconservative

The structure of DNA suggested to Watson and Crick the mechanism by which DNA — hence genes — could be copied faithfully. They proposed that when the time came for DNA to be replicated, the two strands of the molecule

  • separated from each other but
  • remained intact as each served as the template for the synthesis of
  • a complementary strand.

When the replication

Restriction Enzymes

Restriction enzymes are DNA-cutting enzymes found in bacteria (and harvested from them for use). Because they cut within the molecule, they are often called restriction endonucleases.

In order to be able to sequence DNA, it is first necessary to cut it into smaller fragments. Many DNA-digesting enzymes (like those in your pancreatic fluid) can do this, but most of them are no use for sequence work because they cut each molecule randomly. This produces a heterogeneous

DNA Sequencing

DNA sequencing is the determination of the precise sequence of nucleotides in a sample of DNA.

The most popular method for doing this is called the dideoxy method or Sanger method (named after its inventor, Frederick Sanger, who was awarded the 1980 Nobel prize in chemistry [his second] for this achievment).

DNA is synthesized from four deoxynucleotide triphosphates. The top formula shows one of them: deoxythymidine triphosphate (dTTP). Each new nucleotide is added to the