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SCIENCE AS A PROCESS
WHAT DO WE KNOW ABOUT DNA?
HOW DID WE FIGURE IT OUT?
http://profiles.nlm.nih.gov/CC/A/A/A/Z/_/ccaaaz~.jpg
http://en.wikipedia.org/wiki/Rosalind_Franklin
http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg
http://www.3quarksdaily.com/.a/6a00d8341c562c53ef0120a6194d2f970c-600wi
http://www.time.com/time/time100/scientist/profile/watsoncrick.html
Archibald GARROD (1909)
1st to suggest genes dictate phenotypes through enzymes
that catalyze specific reactions in cells
Coined term “inborn errors of metabolism”
Hypothesized that patients with alcaptonuria lack an enzyme
in metabolic pathway
ALCAPTONURIA“Black urine” disease
Lack enzyme to break down alcapton
Builds up in joints (osteoarthritis),
heart valves, and kidney stones
Excess excreted in urine
http://www.nexusediciones.com/images/alcaptonuria04.jpg
Frederick GRIFFITH (1928)
• See the experiment
Bacterial transformation of pneumonia bacteria in mice
http://upload.wikimedia.org/wikipedia/en/thumb/f/f4/Griffithm.jpg/140px-Griffithm.jpg
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=glyco2&part=ch39&rendertype=figure&id=ch39.f1
Oswald AVERY, Colin MACLEOD,
and Maclyn MCCARTY (1944)
Repeated Griffith’s experiment but added enzymes
to destroy different kinds of molecules.
. . . DNA is the transforming molecule
http://profiles.nlm.nih.gov/CC/A/A/A/Z/_/ccaaaz~.jpg
George BEADLE and Edward TATUM (1940’s)
“one gene-one enzyme”
Neurospora bread mold mutants
Each lacks different enzyme in
biochemical pathway
If add missing substance,
mold is able to grow
http://www.nauba-aloke-bangla.com/EBook/Projukti-o-Biggan/top100/Beadle_Tatum.jpg
Experiment images from: Campbell and Reece AP Biology
Alfred HERSHEY and
Martha CHASE (1952)
• See their experiment
DNA = genetic code molecule
http://osulibrary.oregonstate.edu/specialcollections/coll/nonspcoll/catalogue/portrait-hersheychase-600w.jpg
https://www.msu.edu/course/lbs/333/fall/images/HERSHEY2.gif
ROSALIND FRANKLIN and MAURICE WILKINS
Analyzed DNA with X-ray crystallography to try
and determine its structure
1953 - JAMES WATSON & FRANCIS CRICK
used Rosalind Franklin’s X-ray crystallography
images (PHOTO 51) to come up with alpha helix
model for the structure of DNA
http://en.wikipedia.org/wiki/Rosalind_Franklin
http://www.time.com/time/time100/scientist/profile/watsoncrick.html
http://www.pnas.org/content/101/52/17889/F1.medium.gif
Matthew MESELSON
and Franklin STAHL (1958)
DNA copies by semi-conservative model
• See their experiment
http://en.wikipedia.org/wiki/File:DNAreplicationModes.png
MESELSON & STAHL
Images from: http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/106/unit01/6.dnareplicationmodels.html
Grew bacteria for many generations in radioactive (heavy)
15N . . . so all DNA is heavy
Then grow in 14N, centrifuge as generations divide, and
check to see where heavy DNA ends up
http://www.sumanasinc.com/webcontent/animations/content/meselson.html
MESELSON & STAHL
Can tell which model
it is by the banding
patterns of DNA
molecules
SO WHAT ?
Provided evidence for
SEMI-CONSERVATIVE
REPLICATION MODEL
http://www.sumanasinc.com/webcontent/animations/content/meselson.html
Telomeres protect DNA from being degraded
Telomeres become shorter with each replication;
shorter in older cells
Telomerase enzyme lengthens telomeres
Stem cells, germ cells making gametes, and cancer cells
have increased telomerase activity
2009
Nobel Prize
Physiology/Medicine
Discovery of Telomeres
Jack Szostak
Carol Greider Elizabeth Blackburn.