Scientists and DNA Research
Fredrick Griffiths
https://www.youtube.com/watch?v=vQOdDGM5vSg
Hershey & Chase
http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/00724
37316/120076/bio21.swf::Hershey+and+Chase+Experiment
Rosalind Franklin
https://www.youtube.com/watch?v=JiME-W58KpU
Erwin Chargaff
https://www.youtube.com/watch?v=HvJlnujmYcg
Watson & Crick
https://www.youtube.com/watch?v=VegLVn_1oCE
Now do Activity 5.1 Science, Ethics and the Double Helix by reading the procedure and
answering questions # 1 to 3 on page 211.
Griffiths
In this experiment, bacteria from the III-S strain were killed by heat, and their remains were added to II-R
strain bacteria. While neither alone harmed the mice, the combination was able to kill its host. Griffith was
also able to isolate both live II-R and live III-S strains of pneumococcus from the blood of these dead
mice. Griffith concluded that the type II-R had been "transformed" into the lethal III-S strain by a
"transforming principle" that was somehow part of the dead III-S strain bacteria.
Hershey & Chase
The Hershey–Chase experiments were a series of experiments conducted in 1952[1] by Alfred
Hershey and Martha Chase that helped to confirm that DNA is the genetic material. While DNA had been
known to biologists since 1869,[2] a few scientists still assumed at the time that proteins carried the
information for inheritance. In their experiments, Hershey and Chase showed that when bacteriophages,
which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most
of their protein does not. Although the results were not conclusive, and Hershey and Chase were cautious
in their interpretation, previous, contemporaneous and subsequent discoveries all served to prove that
DNA is the hereditary material. Knowledge of DNA gained from these discoveries has applications
inforensics, crime investigation and genealogy.
Rosalind Franklin
Franklin is best known for her work on the X-ray diffraction images of DNA which led to the discovery of
the DNA double helix. According to Francis Crick, her data was key to determining the structure[3] to
formulate Crick and Watson's 1953 model regarding the structure of DNA.[4] Franklin's images of Xray diffraction confirming the helical structure of DNA were shown to Watson without her approval or
knowledge. This image and her accurate interpretation of the data provided valuable insight into the DNA
structure, but Franklin's scientific contributions to the discovery of the double helix are often overlooked.
Erwin Chargaff
Erwin Chargaff proposed two main rules in his lifetime which were appropriately named Chargaff's rules.
The first and best known achievement was to show that in natural DNA the number of guanine units
equals the number of cytosine units and the number of adenine units equals the number of thymine units.
In human DNA, for example, the four bases are present in these percentages: A=30.9% and T=29.4%;
G=19.9% and C=19.8%. This strongly hinted towards the base pair makeup of the DNA, although
Chargaff did not explicitly state this connection himself.
Watson & Crick
When Watson and Crick produced their double helix model of DNA, it was known that most of the
specialized features of the many different life forms on Earth are made possible by proteins. Structurally,
proteins are long chains of amino acidsubunits. In some way, the genetic molecule, DNA, had to contain
instructions for how to make the thousands of proteins found in cells. From the DNA double helix model, it
was clear that there must be some correspondence between the linear sequences of nucleotides in DNA
molecules to the linear sequences of amino acids in proteins. The details of how sequences of DNA
instruct cells to make specific proteins was worked out by molecular biologists during the period from
1953 to 1965. Francis Crick played an integral role in both the theory and analysis of the experiments that
led to an improved understanding of the genetic code