12.1: Identifying the Substance of Genes

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

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

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

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

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