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 DNA12.1 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.