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12.1: Identifying the Substance of Genes
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Investigating bacteria and pneumonia S strain: mouse dies of pneumonia R strain: mouse lives Heat-killed S strain: mouse lives Mix of heat-killed S strain and R strain:
mouse dies Conclusion: some chemical factor was
transferred from dead S-strain to live R-strain cells (transformation). Offspring cells inherited the ability to cause disease chemical factor had to be a gene
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Repeated Griffith’s work Extracted molecules from heat-killed
bacteria and treated it w/ enzymes that destroyed lipids, proteins, carbs, etc. transformation still occurred
Repeated again but used enzymes that broke down nucleic acid (DNA) transformation did not occur
Conclusion: DNA was the transforming factor
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Worked with bacteriophage (virus that infects bacteria) composed of DNA core and protein coat
Grew virus cultures that contained radioactive P-32 and S-35
Proteins contain no P; DNA contains no S This will identify which molecule enters
the bacteria carrying the genetic material Result: all radioactivity in bacteria was
from P, the marker found in DNA Conclusion: Genetic material of
bacteriophage was DNA, not protein
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Hershey and Chase’s experiment confirmed Avery’s findings—many scientists now convinced that DNA was the genetic material found in genes of all living cells
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Storing informationGenes control patterns of developmentGenes carry the info to make a flower
purple Copy information
Before a cell divides it must make a complete copy of every one of its genes
Transmit informationDNA molecules must be carefully sorted
and passed along during cell division