Early DNA Experiments – Guided Notes (1) Frederick Griffith – 1928

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 _____________________________________________________.
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.
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 – ____________________________________.
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).
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.
Watson and Crick discovered the shape of DNA (double helix) in 1953 using information gained
from __________________________, mainly ________________________________________.
Crick actually studied ___________________________ and Watson _____________________
before 1952.
Watson and Crick went to lectures from other scientists concerning DNA and compiled
information they gained from them.
Watson _______________________________________________ showing a vague picture
DNA’s shape (you could tell that it was the same thickness all the way through).
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.