More from Chapters 12-13

 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)

 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.

 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.

 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.

 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."

 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

 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.

 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.

 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)

 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.

 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.

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

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