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Unraveling DNA: Scientific Discoveries and Breakthroughs

Explore the journey of DNA discovery from Mendel to Watson and Crick, detailing experiments by Griffith, Avery, Hershey, and others, leading to the understanding of DNA's structure and replication. Delve into the contributions of scientists like Rosalind Franklin and Meselson & Stahl in elucidating the genetic code and replication models. Learn about telomeres and the Nobel Prize-winning work on their discovery. This comprehensive overview sheds light on the fascinating process of unraveling the mysteries of DNA.

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Unraveling DNA: Scientific Discoveries and Breakthroughs

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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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