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SCIENCE AS A PROCESS. http://profiles.nlm.nih.gov/CC/A/A/A/Z/_/ccaaaz~.jpg. WHAT DO WE KNOW ABOUT DNA? HOW DID WE FIGURE IT OUT?. http://en.wikipedia.org/wiki/Rosalind_Franklin. http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg.

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science as a process
SCIENCE AS A PROCESS

http://profiles.nlm.nih.gov/CC/A/A/A/Z/_/ccaaaz~.jpg

WHAT DO WE KNOW ABOUT DNA?

HOW DID WE FIGURE IT OUT?

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
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
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
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
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 mutants

Each lacks different enzyme in biochemical pathway

If add missing substance,

mold is able to grow

alfred hershey and martha chase 1952
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

slide7

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)
  • See their experiment

DNA copies by semi-conservative model

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

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 stahl10
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

slide11
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

2009Nobel PrizePhysiology/Medicine

Discovery of Telomeres

Jack Szostak Carol Greider Elizabeth Blackburn.

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