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SCIENCE AS A PROCESSWHAT DO WE KNOW ABOUT DNA?HOW DID WE FIGURE IT OUT?
http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg
http://en.wikipedia.org/wiki/Rosalind_Franklin
http://www.time.com/time/time100/scientist/profile/watsoncrick.html
http://www.3quarksdaily.com/.a/6a00d8341c562c53ef0120a6194d2f970c-600wi
http://profiles.nlm.nih.gov/CC/A/A/A/Z/_/ccaaaz~.jpg
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 micehttp://upload.wikimedia.org/wikipedia/en/thumb/f/f4/Griffithm.jpg/140px-Griffithm.jpghttp://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 enzymesto 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”
http://www.nauba-aloke-bangla.com/EBook/Projukti-o-Biggan/top100/Beadle_Tatum.jpg
Experiment images from: Campbell and Reece AP Biology
Neurospora bread mold mutantsEach lacks different enzyme in biochemical pathway If add missing substance, mold is able to grow
Alfred HERSHEY and Martha CHASE (1952)
• See their experiment
DNA = genetic code molecule
http://osulibrary.oregonstate.edu/specialcollections/coll/nonspcoll/catalogue/portrait-hersheychase-600w.jpghttps://www.msu.edu/course/lbs/333/fall/images/HERSHEY2.gif
http://en.wikipedia.org/wiki/Rosalind_Franklin http://www.time.com/time/time100/scientist/profile/watsoncrick.html
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 helixmodel for the structure of DNA
Matthew MESELSON and Franklin STAHL (1958)
• See their experiment
DNA copies by semi-conservative model
http://en.wikipedia.org/wiki/File:DNAreplicationModes.png
http://www.pnas.org/content/101/52/17889/F1.medium.gif
MESELSON & STAHLGrew 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
Images from: http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/106/unit01/6.dnareplicationmodels.html
http://www.sumanasinc.com/webcontent/animations/content/meselson.html
MESELSON & STAHLCan tell which model it is by the bandingpatterns of DNA
molecules
SO WHAT ?
http://www.sumanasinc.com/webcontent/animations/content/meselson.html
Provided evidence forSEMI-CONSERVATIVE REPLICATION MODEL
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
Jack Szostak Carol Greider Elizabeth Blackburn.
2009Nobel PrizePhysiology/MedicineDiscovery of Telomeres