Section 13.1Identifying the Substance of the

Gene

Standard

• LS1.3 Integrate evidence to develop a structural model of a DNA molecule. Using this model, develop and communicate an explanation for how DNA serves as a template for self-replication and encodes biological information.

I Can…

• LS 1.3 I can use historical evidence to identify patterns and model the structure of the DNA molecule.

Key Questions

1. What clues did bacterial transformation yield about the gene?

2. What role did viruses play in identifying genetic material?

3. What is the role of DNA in heredity?

Vocabulary

• Transformation

• Bacteriophage

Griffith

• In 1928, British scientist Frederick Griffith was investigating how bacteria caused pneumonia.

• “S-type” – diseasing-causing bacteria that grew in smooth colonies

• “R-type” – harmless bacteria that grew in rough colonies

1. Injected S-type into mouse… mouse died

2. Injected R-type into mouse… mouse lived

Did the S-type produce a poison that made the mice sick?

Griffith

3. Heated S-type cells, injected dead cells into mouse… mouse lived

(suggesting cause of pneumonia was not a poison)

4. Heat-killed S-type cells + living R-type cells, injected into the mouse…

mouse died

How did the mice die in experiment #4? Neither of those bacteria types made the mice sick on their own. When he examined the lungs of the mice, he found S-type bacteria. How did this happen if the S-type bacteria were dead?

Griffith and Transformation

• Transformation- one strain of bacteria (the R-type harmless) had been changed permanently into another strain (the S-type disease-causing)

• Some kind of “chemical factor” was passed from the heat-killed S-type bacteria to the living R-type bacteria

Griffith’s Experiments

Live S

strain

Avery

• In 1944, Oswald Avery and a team of scientists wanted to identify the molecule that caused transformation in Griffith 4th experiment.

1. Heat-killed S-type + enzymes that destroyed proteins, lipids, carbohydrates, and RNA. Added to the living R-type strain. Injected into mouse. Mouse died (transformation still occurred)

2. Heat-killed S-type + enzymes that destroyed DNA. Added to the living R-type strain. Injected into mouse. Mouse lived (transformation did not occur)

Avery

• By observing bacterial transformation, Avery and other scientists discovered that DNA stores and transmits genetic information from one generation of bacteria to the next.

• Conclusions:

• Avery and his team discovered that DNA stores and transmits genetic information from one generation of bacteria to the next.

• DNA was the transforming factor.

• His work provided evidence that genes were made of DNA.

Hershey and Chase

• Many scientists were skeptical of Avery’s results.

• In 1952, Alfred Hershey and Martha Chase confirmed the genetic importance of DNA.

• Viruses- non-living particles made of a protein coat and a DNA or RNA core

• Bacteriophage- a virus that infects bacteria • Attaches to surface of bacterium and injects genetic information into cell • Viral genes act to produce many new bacteriophages• The cell died and splits open, releasing hundreds of new viruses

Hershey and Chase

• Used radioactive markers to determine if DNA or protein was the genetic material of the virus.

• Because proteins contain almost no phosphorus and DNA contains no sulfur…

• Phosphorus-32 was used to mark DNA• Sulfur-35 was used to mark protein

• Conclusion- confirmed Avery’s conclusion that DNA was the genetic material.

The Role of DNA

Specifically, the DNA molecule must be capable of storing and copying genetic information, as well as putting that information to work in gene expression.

Section 13.1 Exit Ticket

1. What did the experiments of Griffith and Avery show about genetic information?

2. How did the results of the Hershey-Chase experiment strengthen Avery’s conclusions?

3. What are the three key roles of DNA?

The End ☺