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The History of DNA Gregor Mendel-1866 –Determined Unit characters were the method of passing on traits for inheritance Friedrich Meischer - 1868 –Studied.

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Presentation on theme: "The History of DNA Gregor Mendel-1866 –Determined Unit characters were the method of passing on traits for inheritance Friedrich Meischer - 1868 –Studied."— Presentation transcript:

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3 The History of DNA Gregor Mendel-1866 –Determined Unit characters were the method of passing on traits for inheritance Friedrich Meischer –Studied nuclei of pus cells obtained from discarded surgical bandages –Detected a phosphorus-containing substance that he named nuclein.

4 Frederick Griffith 1928 : Work with Bacteria –Found that DNA taken from a virulent (disease-causing) strain of bacteria (Streptococcus pneumoniae) –Transformed a non-virulent form of the bacterium into a virulent form.

5 Oswald Avery, Colin MacLeod, and Maclyn McCarty 1943 Continued the study of Transformation principle

6 Mendel Meischer Griffith Avery McCartyMacLeod

7 Transformation Of Bacteria Two Strains Of Streptococcus Smooth Strain w/Capsule (Virulent) Rough Strain (Harmless) Capsule

8 Experimental Transformation Of Bacteria -Griffiths Experiment Control OUCH! Rough Smooth (virulent)

9 The History of DNA Alfred Hershey and Martha Chase –radioactive isotope tracer experiment –bacterial virus (bacteriophage T2) infects a host cell ( bacterium Escherichia coli) –found that T2 virus DNA, not its protein coat, enters the host cell –genetic information for replication of the virus

10 Using S 35 Bacteria grown in normal non- radioactive media T 2 grown in media containing S 35 incorporate S 35 into their proteins Blending causes phage protein coat to fall off T2 attach to bacteria and inject genetic material Is protein the genetic material? When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet. The supernatant is radioactive, but the pellet is not. Did protein enter the bacteria?

11 Using P 32 Bacteria grown in normal non- radioactive media T2 grown in P 32 containing media incorporate P 32 into their DNA Blending causes phage protein coat to fall off T2 attach to bacteria and inject genetic material Is DNA the genetic material? When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet The pellet is radioactive, but the supernatant is not. Did DNA enter the bacteria?

12 The History of DNA Structure Erwin Chargaff Chargaffs rule – four bases may occur in varying proportions in DNA of different organisms –# of A = # of T, w/ two hydrogen bonds – = # of G and C are present w/ 3 hydrogen bonds Rosalind Franklin and Maurice Wilkins –X-ray diffraction study concluded DNA fibers have two strands.

13 The History of DNA Structure James Watson and Francis Crick - University of Cambridge Worked on problem of making a DNA molecule model that was double stranded but also had the specific A - T and G - C base equivalencies Solution-double helical structure for DNA.

14 Chargaff Franklin Wilkins

15 Watson and Crick


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