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In 1928, Frederick Griffith, an English army doctor,
wanted to make a vaccine against a bacteria
named Streptococcus pneumoniae, which caused a
type of pneumonia. Since the time of Pasteur, about
50 years before, vaccines had been made using
killed microorganisms which could be injected into
patients to elicit the immune response of live cells
without risk of disease. Though he failed in making
the vaccine he stumbled on a demonstration of the
transmission of genetic instructions by a process
we now call the "transformation principle".
• He found that the bacterium had two forms
when grown on agar plates, a smooth (S)
and a rough (R) form. The R bacteria were
harmless, but the S bacteria were lethal
when injected into mice. Heat-killed S cells
were also harmless - the same effect seen
by Pasteur. However, surprisingly when
live R cells were mixed with killed S cells
and injected into mice the mice died, and
the bacteria rescued from the mice had
been "transformed" into the S type.
• This experiment strongly implied that
genetic material had been transferred from
the dead to the live cell. It was hard to be
certain of this, or to know what exactly
genetic material was transferred and was
responsible for the transformation process.
• http://www.juliantrubin.com/bigten/dnaexp
eriments.html
For many years, genetic information was
thought to be contained in cell protein.
Continuing the research done by
Frederick Griffith in 1928, Avery worked
with MacLeod and McCarty on the
mystery of inheritance. He had received
emeritus status from the Rockefeller
Institute in 1943, but continued working
for five years, proving that not all
breakthrough discoveries are achieved
by younger people (by this time he was
in his late sixties).
Techniques were available to remove
various organic compounds from
bacteria, and if the remaining organic
compounds were still able to cause R
strain bacteria to transform then the
substances removed couldn't be the
carrier of genes. S strain bacteria first
had the large cellular structures
removed.
Then they were treated with protease
enzymes, which removed the proteins
from the cells before the remainder was
placed with R strain bacteria. The R strain
bacteria transformed, meaning that
proteins didn't carry the genes for causing
the disease. Then the remnants of the R
strain bacteria were treated with a
deoxyribonuclease enzyme which
removed the DNA. After this treatment, the
R strain bacteria no longer transformed.
This indicated that DNA was the carrier of
genes in cells.
• http://faculty.uca.edu/~johnc/mbi1440.htm
• http://www.juliantrubin.com/bigten/dnaexperiments.html
• http://en.wikipedia.org/wiki/Oswald_Avery
• http://www.accessexcellence.org/RC/VL/GG/hershey.htm
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