Biology CP
Ch. 10 - The Discovery of DNA
1928: Frederick Griffith’s Experiment
 Tried to find a vaccine for ______________________.
 Studied two strains of Streptococcus pneumoniae, R cells and S cells, by injecting them
into mice.
 “S” strain are virulent (causes disease)
 “R” strain are avirulent
 Griffith injected mice with strains of live and dead “S” and “R” bacteria.
Griffith’s Data
Strepococcus pneumoniae
strain
Result on mouse:
Griffith’s conclusion- The Transforming Principle
 The dead S bacteria transferred an inheritable material to the R strain (heredity: passing
on of traits)
 As a result, the living R bacteria were _______________ into the S strain.
1940’s: Oswald Avery’s Experiment
 Repeated Griffith’s experiments but removed the___________________, ____________,
or______________ molecules.
 Observed which molecule was responsible for “transforming” the R bacteria into S.
Avery’s Data
Dead S strain with…
Result when S strain is mixed with live R strain:
Proteins removed
DNA removed
RNA removed
Avery’s Conclusion
 _______________is the hereditary material that transformed R bacteria into S bacteria.
1952: Alfred Hershey and Martha Chase’s Experiment
 Studied_________________________ (viruses that infect bacteria).
1. Used radioactive tags to identify DNA (32P) and protein (35S)
2. Infected bacteria with the virus.
3. Used blender to remove virus from the surface of the bacteria.
4. Observed what molecule was transferred from the virus into the infected bacteria.
Hershey and Chase’s Observations
 Radioactive protein molecules found ________________ bacteria.
 Radioactive DNA found_____________ bacteria
Hershey and Chase’s Conclusions
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
1950’s Watson and Crick
 Discovered that the structure of DNA is a ____________________ _____________
o two chains that wrap around each other.
Franklin and Wilkins
 Took X-ray diffraction photographs of _____________crystals, which led Watson and
Crick to their discovery.
3 parts of DNA:
1.
2.
3.
These make up the basic unit of DNA, which is called the ___________.
4 Nitrogenous Bases
1.
2.
3.
4.
Structure of DNA
 The backbone of alternating _____ and _________ are like the handrails
 The__________ ____ are like the rungs/ steps of the ladder.
Complementary Base Pairing
 Adenine bonds with ________
 Guanine bonds with________
o Bonded by ________ ______.
o The order of the bases is called the ______ _____________.
Exit Ticket
1. If one strand of DNA has the following base sequence, what sequence would the
complementary strand contain?
ATAGCAGCT
2. What are the two components of the DNA backbone (railing of the staircase)?
3. Name at least two scientists that contributed to deriving the structure of DNA.