The History of DNA All life on earth uses a chemical called DNA to carry its genetic code or blueprint. In this lesson we be examining the structure of this unique molecule. {Point out the alligator’s eyes in the first picture.} By the way, can you make out what this is? *************************************************************** [The goal of this presentation is to introduce high school biology students to the chemical structure of DNA. It is meant to be presented in the classroom while accompanying the teacher’s lecture, under the control of the teacher.]

The History of DNA Gregor Mendel-1866 Determined “Unit characters” were the method of passing on traits for inheritance Friedrich Meischer - 1868 Studied nuclei of pus cells obtained from discarded surgical bandages Detected a phosphorus-containing substance that he named nuclein.

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.

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

Meischer Mendel Griffith MacLeod McCarty Avery

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

Transformation Of Bacteria -Griffith’s Experiment Smooth (virulent) OUCH! Control Rough Control Control Experimental

The History of DNA Alfred Hershey and Martha Chase - 1952 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

Using S35 Did protein enter the bacteria? T 2 grown in media containing S35 incorporate S35 into their proteins Bacteria grown in normal non-radioactive media When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet. T2 attach to bacteria and inject genetic material The supernatant is radioactive, but the pellet is not. Mix-O-Matic Blending causes phage protein coat to fall off Did protein enter the bacteria? Is protein the genetic material?

Using P32 Did DNA enter the bacteria? Is DNA the genetic material? T2 grown in P32 containing media incorporate P32 into their DNA Bacteria grown in normal non-radioactive media When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet T2 attach to bacteria and inject genetic material The pellet is radioactive, but the supernatant is not. Mix-O-Matic Blending causes phage protein coat to fall off Did DNA enter the bacteria? Is DNA the genetic material?

The History of DNA Structure Erwin Chargaff- 1940 - “Chargaff’s 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.

The History of DNA Structure James Watson and Francis Crick - University of Cambridge -1953 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.

Franklin Chargaff Wilkins

Watson and Crick