Transcript Chapter 12: DNA

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 Rstrain 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


Genes control patterns of development
Genes carry the info to make a flower purple
 Copy

information
information
Before a cell divides it must make a complete
copy of every one of its genes
 Transmit

information
DNA molecules must be carefully sorted and
passed along during cell division