Science As a Process


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 ALCAPTONURIABlack urine disease Lack enzyme to break down alcapton Builds up in joints (osteoarthritis), heart valves, and kidney stones

Excess excreted in urine Frederick GRIFFITH (1928) See the experiment Bacterial transformation of pneumonia bacteria in mice Oswald AVERY, Colin MACLEOD, and Maclyn

MCCARTY (1944) Repeated Griffiths experiment but added enzyme to destroy different kinds of molecules. . . . DNA is the transforming molecule George BEADLE and Edward TATUM (1940s) one gene-one enzyme

Neurospora bread mold mutants Each lacks different enzyme in biochemical pathway If add missing substance, mold is able to grow Experiment images from: Campbell and Reece AP Biology Alfred HERSHEY and Martha CHASE (1952) See their experiment

DNA = genetic code molecule ROSALIND FRANKLIN and MAURICE WILKINS Analyzed DNA with X-ray crystallography to try and determine its structure 1953 - JAMES WATSON & FRANCIS CRICK used Rosalind Franklins X-ray crystallography mages (PHOTO 51) to come up with alpha helix

model for the structure of DNA Matthew MESELSON and Franklin STAHL (1958) DNA copies by semi-conservative model

See their experiment Images from: 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 MESELSON & STAHL Can tell which model it is by the banding patterns of DNA molecules SO WHAT ? Provided evidence for SEMI-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 2009 Nobel Prize Physiology/Medicine

Discovery of Telomeres Jack Szostak Carol Greider Elizabeth Blackburn.

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