Transcript The History of the Discovery of DNA

The History of the
Discovery of DNA
Griffith – 1928
Studied Streptococcus pneumoniae, the bacterium that causes pneumonia.
The outer coat of the bacterium is either smooth (S) or rough (R).
Griffith injected both strains into mice and found that only the S bacteria were
deadly; live R and heat-killed S were harmless individually.
BUT – if the live R and heat-killed S were injected together, mice died and living
S bacteria appeared.
Griffith concluded that something from the dead S bacteria converted R
bacteria into the S form.
He called it the “transforming principle.”
Avery – 1943
Avery put heat-killed S bacteria into a test tube.
When he added enzymes that destroy proteins, the S bacteria were still able to
transform R bacteria.
But when DNA destroying enzymes were added, the R bacteria couldn’t be
transformed.
Avery concluded that DNA was the “transforming” substance.
Chargaff – 1950
Chargaff studied the chemical composition of the DNA molecule.
Chemical studies of DNA had revealed that it contained a type of sugar called
deoxyribose, plus a phosphate group and four different molecules, or bases,
called adenine, thymine, guanine, and cytosine.
Chargaff realized that the amount of adenine in a DNA sample always equaled
the amount of thymine, and the amount of cytosine always equaled the amount
of guanine.
This relationship, called Chargaff’s law, helped scientists who came after him
decipher the three-dimensional structure of the molecule.
Hershey and Chase – 1952
Hershey and Chase worked with bacteriophages.
They knew that the viruses were transferring hereditary information to infected
bacteria, but they weren’t sure if the information was protein or DNA.
So they infected bacteria with viruses that had either radioactively labeled
proteins or radioactively labeled DNA.
Infected bacteria became radioactive only from the DNA, proving that DNA is
the molecule of heredity.
Franklin – 1952
Franklin was an expert at x-ray diffraction, a technique that
uses focused beams of x-rays to produce photographs of the
crystallized forms of molecules.
As the x-rays pass through the molecule, they bounce off—
or diffract—before striking photographic film.
The patterns produced on the film by those bouncing x-rays
can then be used to reconstruct the three-dimensional
structure of the molecule.
Franklin’s images of DNA ultimately revealed its exact
structure.
Watson and Crick – 1953
Watson and Crick had been tinkering with large three-dimensional models of
DNA, trying to determine the structure of the molecule.
After viewing on of Franklin’s x-ray diffraction images, which they did without
her knowledge, they figured out that DNA is made up of two mirror-image
strands composed of stacked DNA nucleotides linked together into a twisting
double helix.
The double helix resembles a ladder, with the sugar and phosphate as the rails
and the nitrogen bases held by hydrogen bonds as the rungs.
For the discovery, they received the Nobel Prize in Chemistry. Franklin’s
colleague, Wilkins, also received the award, but not Franklin as she had died.
Sanger – 1975
The two-time Nobel Prize winner developed a method of sorting DNA fragments
so that the exact sequence of nitrogen bases can be determined.
Genentech – 1977-1979
The world’s first genetic engineering company was the first to genetically modify
bacteria to produce human hormones, including insulin and human growth
hormone.
Mullis – 1985
Mullis published the first paper describing polymerase chain reaction (PCR), a
chemical reaction that can be used to make many copies of even tiny amounts
of DNA quickly.
National Institutes of Health – 1990
The first federally approved gene replacement therapy was conducted on a 4year-old girl with a rare form of immune deficiency disease.
Calgene, Inc. – 1993
The California biotech company produced the first commercially grown
genetically engineered food—a tomato—that was granted a license for human
consumption from the US FDA.
Roslin Institute – 1996
Dolly the sheep, the first mammal to ever be cloned from the cells of an adult
animal, was born at the Roslin Institute in Scotland.
International Human Genome
Sequencing Consortium – 2003
Scientists with the Human Genome Project, begun in 1990, announced the
sequencing of the human genome to an accuracy of 99.99%.