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