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

Matthew MESELSON and Franklin STAHL (1958) 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

Images from: http://instruct1. cit. cornell MESELSON & STAHL 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.