Transcript DNA - TeacherWeb

The History of DNA
Unlocking the code of life
Friedrich Meischer:
First to Isolate DNA
DNA
appeared too
simple to be
the carrier of
all the
information
needed to
make proteins
Is it DNA?
In 1928, Griffith found out that the
information carried in the cell could be
transferred to another cell.
He called this transfer
“transformation”.
He did not yet know about DNA and
the prevailing thought of the time was
that protein was the more likely
culprit.
Frederick Griffith
Griffith conclusions.
When he injected a
mixture of heatkilled, diseasecausing bacteria
and live harmless
bacteria into mice
the mice developed
pneumonia.
Focusing in on an answer.
Avery, MacLeod and McCarty
repeated the Griffith experiment
except that they killed the heat-killed
bacteria with enzymes that destroyed
proteins, lipids, carbohydrates and
RNA.
Transformation still occurred.
When they destroyed the DNA the
transformation did not occur.
Oswald Avery, Collin MacLeod and
Maclyn McCarty: It is DNA!
More evidence…….
Hershey and Chase developed an
experiment that conclusively
determined that it was the DNA and
not protein that allowed information to
be passed down to the next
generation.
Hershey and Chase
Hershey and Chase conclusions
Because only the
radioactive
phosphorus was
found in the
bacteria, only the
DNA was injected
into the cell.
Phosphorus is
only found in DNA.
Sulfur is only
found in protein.
Another puzzle piece…..
P. A. Levene discovered that DNA
was composed of 4 nitrogenous
bases:
Guanine (g)
Adenine (a)
Thymine (t)
Cytosine ( c)
Levene
Erwin Chargaff’s Rules
Chargaff determined that different
species carry differing amounts of the
nitrogenous bases.
He also determined that some of the
bases always showed equality:
C=G and A=T
Chargaff
The helical structure is
revealed.
Discovery of the DNA double helix
came in 1953.
Rosalind Franklin and Maurice
Wilkins - took an X-ray
crystallography photo of DNA showing
the double helix structure.
Franklin and Wilkins
EUREKA!!!!!!!
James Watson and Francis Crick took
all of the available evidence and
determined the structure of the
“molecule of life.”
It is a twisting double helix.
Watson and Crick