1 Review List the conclusions that Griffith and Avery
drew from their experiments
Identify Variables What experimental variable did
Avery use when he repeated Griffith’s work
2 Review What conclusion did Hershey and Chase draw
from their experiments
Infer Why did Hershey and Case grow viruses in
cultures that contained both radioactive substances?
What might have happened if they only used one
radioactive substance
3 Choose Griffith, Avery, or Hershey and Chase and
develop a flow chart that shows how they used
various scientific methods. You may want to refer to
Ch 1 for descriptions of the scientific method.
CH 12 DNA
12.1 Identifying the Substance of Genes
Frederick Griffith


Two different strains of same bacteria one strains
caused pneumonia
Grew both in culture plates.


Griffith injected mice with disease-causing bacteria,
the mice developed pneumonia and died
He injected mice with harmless bacteria, the mice
stayed healthy.


Griffith took a culture of the S strain, heated the
cells to kill them, and then injected the heat-killed
bacteria into laboratory
Mice survived.


He mixed the heat-killed, S-strain bacteria with live,
harmless bacteria from the R strain and injected it
into laboratory mice
Injected mice developed pneumonia, and died.

Some chemical factor changed harmless bacteria
into disease-causing bacteria was transferred from
the heat-killed cells of the S strain into the live cells
of the R strain.
Transformation

Process where one strain of bacteria is changed by
a gene from another strain of bacteria.
Avery



Extracted a mixture of various molecules from the
heat-killed bacteria
Added enzymes that broke down proteins, lipids,
carbohydrates, and RNA
Transformation still occurred.

Avery’s team repeated the experiment using
enzymes that would break down DNA
Transformation did not occur

DNA is the transforming factor.

Hershey and Chase


Experiment with bacteriophages
Confirmed Avery’s results .
Bacteriophages
Virus that infects bacteria
 Attaches to the surface of the bacterial cell
 Injects its genetic
information
 New bacteriophages
are produced.

Hershey-Chase Experiment

What part of the virus - the protein coat or the
DNA core - entered the bacterial cell.
Hershey-Chase Experiment


Grew viruses in cultures containing radioactive
isotopes of phosphorus-32 (P-32) sulfur-35 (S-35)
Proteins contain almost no phosphorus and DNA
contains no sulfur.



If they found S-35 in the bacteria then the virus’s
protein coat had been injected into the bacteria
If they found P-32 then the DNA core had been
injected
They mixed the marked viruses with bacterial cells.


In the bacteria they found phosphorus P-32 , the
marker found in DNA
DNA was the genetic material.
The Role of DNA

Capable of storing, copying, and transmitting
genetic information in a cell.
Storing Information


Main job is of DNA is to store information
Genes control patterns of development.
Copying Information

Before a cell divides, it must make a complete copy
of its genes.
Transmitting Information


When a cell divides each cell receives a complete
copy of the genetic information
Loss of any DNA during meiosis might mean a loss
of valuable genetic information.