1. More from Chapters 12-13

2.  1928 – Frederick Griffith is trying to develop a vaccine for Streptococcus pneumoniae, which causes pneumonia  Griffith was able to isolate 2 strains of the bacterium: one with a rough surface (R) and one with a smooth surface (S)

3.  Griffith injected one group of mice with the smooth (virulent) strain and these mice died after a few days.  He then injected another group with the rough (nonvirulent) strain and these mice continued to be healthy.

4.  Griffith took a heat-killed strain of the smooth bacteria and injected it into mice and observed that they did not die.  Griffith's fourth experiment was to inject heat treated, killed, smooth strain mixed with the rough strain.

5.  He found that after a few days the mice died. The blood of the dead mice showed high levels of virulent pneumococcus.  Griffith theorized that some type of transformation takes place from the virulent to the non-virulent strain for it to synthesize a new polysaccharide coat.

7.  Expanding on the work of Griffith, found that the agent responsible for genetic transferring is the nucleic acid DNA and not protein as most biochemists theorized at the time.  In 1944 Avery and his coworkers, McCarty and MacLeod, discovered the "transforming principle."

8.  First they treated the bacteria with centafugation, which eliminates large cellular pieces. The result: bacteria still transformed  Added protease, which removes all proteins. The result: bacteria still transformed

9.  Treated the bacteria with deoxyribonuclease, which eliminates all DNA. The result: no transformation in the bacteria  The trio concluded that DNA is the cause of transformation, where in this experiment virulence is inherited.

10.  Noticed a pattern in the amounts of the four bases: adenine, guanine, cytosine, and thymine.  Took samples of DNA of different cells and found that the amount of adenine was almost equal to the amount of thymine.

11.  The amount of guanine was almost equal to the amount of cytosine.  Thus you could say: A=T, and G=C. This discovery later became Chargaff’s Rule. (Complimentary base pairing)

13.  Decided to try to make a crystal of the DNA molecule.  If they could get DNA to crystallize, then they could make an x-ray pattern, thus resulting in understanding how DNA works.

14.  They obtained an x-ray pattern.  The pattern appeared to contain rungs, like those on a ladder between to strands that are side by side.  It also showed by an “X” shape that DNA had a helix shape.

17. DNARNA Has deoxyriboseHas ribose Has thymineHas uracil Double HelixSingle Strand Has instructions to make proteins Carries out protein making instructions

18.  http://upload.wikimedia.org/wikipedia/commons/t humb/6/6a/Griffith_experiment.svg/450px- Griffith_experiment.svg.png http://upload.wikimedia.org/wikipedia/commons/t humb/6/6a/Griffith_experiment.svg/450px- Griffith_experiment.svg.png  http://library.thinkquest.org/20465/griffith.html http://library.thinkquest.org/20465/griffith.html  http://library.thinkquest.org/20830/Textbook/Histor yofDNAResearch.htm http://library.thinkquest.org/20830/Textbook/Histor yofDNAResearch.htm  http://www.mun.ca/biology/scarr/CG_Chargaff.gif http://www.mun.ca/biology/scarr/CG_Chargaff.gif  http://www.chemistry.msu.edu/Portraits/images/fra nklinc.jpg http://www.chemistry.msu.edu/Portraits/images/fra nklinc.jpg  http://genome.jgi-psf.org/images/dna.jpg http://genome.jgi-psf.org/images/dna.jpg  http://www.nndb.com/people/979/000030889/mauri ce-wilkins-MED.jpg http://www.nndb.com/people/979/000030889/mauri ce-wilkins-MED.jpg