Early DNA Experiments – Guided Notes
(1) Frederick Griffith – 1928
Griffith’s experiments showed that hereditary material can __________________________________
_____________________________________.
 In 1928 Griffith was studying a bacterium called Streptococcus pneumoniae. He was trying to
__________________________________________ against a virulent strain of the bacterium.
 _____________ – disease causing
 _____________– a substance that is prepared from killed or weakened microorganisms
& introduced into the body to protect it from future infection by that microorganism.
 S bacteria is ___________________ because it has a ___________________. The capsule
protects it from attacks by the __________________________________. It is able to survive
long enough in the human body to ________________________________________.
 R bacteria is __________________________ because it lacks a___________________. Without
the capsule it is left defenseless against the human immune system. Therefore it is destroyed in
the human body _____________________________________________________.
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Griffith’s experimental procedure
Injected mouse with ________________________________ (w/o capsule).
 DID NOT kill mice
Injected mouse with ________________________________ (w/ capsule).
 Killed mice
Injected mouse with ________________________________.
 DID NOT kill mice
Injected mouse with _____________________________________________________________.
 Killed mice
Griffith’s Conclusion
The R bacteria ___________________________ found in the ________________________ and
became ___________________________________.
The transfer of genetic material from ____________________________________ or from one
organism to another organism is called _____________________________.
(2) Chargaff - 1950
• Discovered that ______________________________ and _____________________________
occurred in equal percentages in DNA.
• For Example: If you had ___ Adenine and ____ Cytosine then you would have ____ Thymine and
___ Guanine.
• Led to base pairing discovery (that A pairs with T and that C pairs with G)
(3) Hershey and Chase – 1952
Hershey and Chase confirmed that __________________________________, is the hereditary material.
 In 1952, two researchers, Martha Chase and Alfred Hershey, set out to test whether ________
___________________ was the hereditary material viruses transfer when viruses enter bacteria.
 _________________________ - is a virus that infects bacteria.
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Hershey and Chase’s experimental procedure
Grew bacteriophage (with ____________________________) in dish of e.coli (sulfur is only
found in __________________)
Grew bacteriophage (with _____________________________ ) in dish of e.coli (phosphorous is
only found in ____________________)
They traced the radioactive elements that had entered the e. coli to see which one was injected
into the cell.
The ___________ of the virus and ____________________ was what was in the e.coli causing it
to _________________________________________________.
Hershey and Chase’s conclusion
 Hershey and Chase confirmed that _________________________________________________
____.
(4) Watson and Crick – 1953
Watson and Crick used the information gathered by others to determine one of the most important
discoveries in human history – ____________________________________.
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Until Hershey and Chase’s experiment, most people believed that ______________________
________________________ (because protein was involved in basically everything to do with
cells and because it was believed DNA’s structure was too simple to encode the secret to life).
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After the Hershey and Chase experiment in 1952 proved DNA was in fact the hereditary
material, the race was on to discover it’s structure to gain a better understanding of it.
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Watson and Crick discovered the shape of DNA (double helix) in 1953 using information gained
from __________________________, mainly ________________________________________.
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Crick actually studied ___________________________ and Watson _____________________
before 1952.
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Watson and Crick went to lectures from other scientists concerning DNA and compiled
information they gained from them.
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Watson _______________________________________________ showing a vague picture
DNA’s shape (you could tell that it was the same thickness all the way through).
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Watson, Crick, and Wilkins received a Nobel prize from it while Franklin (who did most of the
work) died from cancer due to her exposure to X-rays.