Experiments by thefollowing scientists provided critical information concerningD
ID: 5735 • Letter: E
Question
Experiments by thefollowing scientists provided critical information concerningDNA. Describe each classical experiment and how it providedevidence for the chemical nature of a gene/ Hershey and Chase Griffith and Avery Meselson and stahl Experiments by thefollowing scientists provided critical information concerningDNA. Describe each classical experiment and how it providedevidence for the chemical nature of a gene/ Hershey and Chase Griffith and Avery Meselson and stahl Hershey and Chase Griffith and Avery Meselson and stahlExplanation / Answer
In their first experiment, they labeled the DNA of T4 phages with radioactive Phosphorus-32 (the element phosphorus is present in DNA but not present in any of the 20 amino acids from which proteins are made). They allowed the phages to infect E. coli, then placed the protein shells from the infected cells with a blender and separated the cells and viral coats by using a centrifuge. They found that the radioactive tracer was not visible only in the pellet of bacterial cells and not in the supernatant containing the protein shells.
In their second experiment, they labeled the phages with radioactive Sulfur-35 (Sulfur is present in the amino acids cysteine and methionine, but not in DNA). After separation, the radioactive tracer then was found in the protein shells, but not in the infected bacteria, supporting the hypothesis that the genetic material which infects the bacteria is DNA.
Griffith & Avery
Griffith used two strains of Diplococcus pneumoniae (which infects mice), a type III-S (smooth) and type II-R (rough) strain. The III-S strain covers itself with a polysaccharide capsule that protects it from the host's immune system, resulting in the death of the host, while the II-R strain doesn't have that protective capsule and is defeated by the host's immune system. A German bacteriologist, Fred Neufeld, had discovered the three pneumococcal types (Types I, II, and III) and discovered the Quellung reaction to identify them in vitro.[3] Until Griffith's experiment, bacteriologists believed that the types were fixed and unchangeable, from one generation to another.
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