Milestones in DNA History
1869 Johann Friedrich Miescher identifies a weakly acidic
substance of unknown function in the nuclei of human white blood cells.
This substance will later be called deoxyribonucleic acid, or DNA.
1912 Physicist Sir William Henry Bragg, and his son,
Sir William Lawrence Bragg, discover that they can deduce the atomic structure
of crystals from their X-ray diffraction patterns. This scientiFic tool
will be key in helping Watson and Crick determine DNA's structure.
Pholo courtesy of Cold Spring Harhor Lahoratory Archives.
1924 Microscope studies using stains for DNA and protein
show that both substances are present in chromosomes.
1928 Franklin Griffith, a British medical officer, discovers
that genetic information can be transferred from heat-killed bacteria cells
to live ones. This phenomenon, called transformation, provides the first
evidence that the genetic material is a heat-stable chemical.
1944 Oswald Avery, and his colleagues Maclyn McCarty
and Colin MacLeod, identify Griffith's transforming agent as DNA. However,
their discovery is greeted with skepticism, in part because many scientists
still believe that DNA is too simple a molecule to be the genetic material.
1949 Erwin Chargaff, a biochemist, reports that DNA
composition is speciesspecific; that is, that the amount of DNA and its
nitrogenous bases varies from one species to another. In addition, Chargaff
finds that the amount of adenine equals the amount of thymine, and the amount
of guanine equals the amount of cytosine in DNA from every species.
1953 James Watson and Francis Crick discover the molecular
structure of DNA.
Photo by A.C. Barrington Brown, courtesy of Cold Spring
Harbor Laboratory Archives.
1962 Francis Crick, James Watson, and Maurice Wilkins
receive the Nobel Prize for determining the molecular structure of DNA.
Milestones in Biotechnology
1909 British physician Archibald Garrod first proposes
the relationship between genes and proteins. He hypothesizes that genes
might be involved in creating the proteins that carry out the chemical reactions
of metabolism.
1930s Through experimentation with mutant strains of
Neurospora bread mold, George Beadle and Edward Tatum support Garrod's hypothesis.
This evidence will give rise to the "one gene-one proteinH hypothesis,"
that each protein in a cell results from the expression of a single gene.
1957 During a dysentery epidemic in Japan, biologists
discover that some strains of bacterium are resistant to antibiotics. Later
scientists will find that this resistance is transferred by olasmids.
1961 Sidney Brenner and Francis Crick establish that
groups of three nucleotide bases, or codons, are used to specify individual
amino acids.
Pholo courtesy of Huntington Potter and David Dressler.
1966 The genetic code is deciphered when biochemical
analysis reveals which codons determine which amino acids.
1970 Hamilton Smith, at Johns Hopkins Medical School,
isolates the first restriction enzyme, an enzyme that cuts DNA at a very
specific nucleotide sequence. Over the next few years, several more restriction
enzymes will be isolated.
1972 Stanley Cohen and Herbert Boyer combine their efforts
to create recombinant DNA. This technology will be the beginning of the
biotechnology industry.
Pholo courtesy of Sandra Black and Lillian Castro.
1976 Herbert Boyer cofounds Genentech, the first firm
founded in the United States to apply recombinant DNA technology
1978 Somatostatin, which regulates human growth hormones,
is the first human protein made using recombinant technology.
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Resource Book Index: Stories from the Scientists
