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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.

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SCIENCE AS A PROCESS

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  1. 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

  2. Gregor Mendel 1840’s • True breeding plants crossbred to yield F1 of all one genotype, F2 had a predictable ratio of resemblance to one or the other parent. • Heredity packaged in transferable units. • Laws of Segregation, Independent Assortment

  3. Thomas Hunt Morgan • Early 1900’s • Fruit fly genes are proteins and were associated with chromosomal inheritance. • Crossing over • Linked traits

  4. 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

  5. Oswald AVERY (1944)Colin MACLEOD, and Maclyn MCCARTY 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

  6. 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

  7. Erwin Chargraff1947 • Composition of DNA and concentration of nitrogenous bases • Predictable ratio, changes from species to species • T to A • G to C

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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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