13.1 Ecologists Study Relationships

12.1 Identifying the Substance of Genes

Key Questions:

-What clues did bacterial transformation yield about the gene?

-What role did bacterial viruses play in identifying genetic material?

-What is the role of DNA in heredity?

Key Questions:

-What clues did bacterial transformation yield about the gene?

-What role did bacterial viruses play in identifying genetic material?

-What is the role of DNA in heredity?

Chapter12 DNA

Vocabulary:Transformationbacteriophage

Vocabulary:Transformationbacteriophage

13.1 Ecologists Study Relationships

What is DNA?A large molecule found in the nucleus of cells that is responsible for heredity (passing of genes from parent to offspring).

Warm-up

How do we know the function of DNA?

DNA was identified as the genetic material responsible for heredity through a series of experiments.

Gene: Sequence of DNA that codes for a protein and thus determines a trait; factor that is passed from parent to offspring

8.1 Identifying DNA as the Genetic Material

Rosalind Franklin 1952Watson and Crick 1953

• Rosalind Franklin determined what elements made up DNA (N & P)

The discovery of DNA

• Watson and Crick used Franklin’s data to describe the shape of DNA as a double helix

Watson Crick

Franklin

Double Helix

8.1 Identifying DNA as the Genetic Material12.1 Identifying the Substance of Genes12.1 Identifying the Substance of Genes

• What clues did bacterial transformation yield about the gene?

• What clues did bacterial transformation yield about the gene?

DNA Structure was not determined until 1950

•-Scientists had to first understand the function of DNA

•It took many scientists observing and experimenting to determine DNA’s structure

DNA Structure was not determined until 1950

•-Scientists had to first understand the function of DNA

•It took many scientists observing and experimenting to determine DNA’s structure

8.1 Identifying DNA as the Genetic Material

KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

How do we know the function of DNA?

8.1 Identifying DNA as the Genetic Material

Griffith (1924-41): finds “transforming material” (genetic material) • Griffith experimented with the bacteria that cause pneumonia.

• He used two forms: the S form (deadly/smooth colonies) and the R

form (not deadly/rough edged colonies).

11What clues did bacterial transformation yield about the gene?

Why?Why?

But why did they die?

But why did they die?

Concluded: A “transforming material” passed from dead S bacteria to live R bacteria, making them deadly and this transforming factor had to be a gene.

Concluded: A “transforming material” passed from dead S bacteria to live R bacteria, making them deadly and this transforming factor had to be a gene.

8.1 Identifying DNA as the Genetic Material

• Avery wanted to determine: What was the molecular cause for transformation?

• Avery isolated and purified Griffith’s transforming factor.• Avery compared the chemical make-up of four samples

of Griffith’s transforming material to the chemical make-up of DNA.

• Avery wanted to determine: What was the molecular cause for transformation?

• Avery isolated and purified Griffith’s transforming factor.• Avery compared the chemical make-up of four samples

of Griffith’s transforming material to the chemical make-up of DNA.

11What clues did bacterial transformation yield about the gene?

Griffith didn’t know what made up genes so…Griffith didn’t know what made up genes so…

8.1 Identifying DNA as the Genetic Material

Avery’s Data

11

Avery’s Conclusion:– Chemical tests showed the chemical make-up of the

unknown transforming samples matched that of DNA.

Avery’s Conclusion:– Chemical tests showed the chemical make-up of the

unknown transforming samples matched that of DNA.

What clues did bacterial transformation yield about the gene?

8.1 Identifying DNA as the Genetic Material

Hershey and ChaseHershey and Chase

• Used Viruses that infect bacteria called… Bacteriophages– A bacteriophage is a kind of virus that infects bacteria

• Used Viruses that infect bacteria called… Bacteriophages– A bacteriophage is a kind of virus that infects bacteria

What role did bacterial viruses play in identifying genetic material?

8.1 Identifying DNA as the Genetic Material

• Hershey and Chase studied viruses that infect bacteria (bacteriophages)

• Results - Tagged DNA was found inside the bacteria; tagged proteins were not!

• They tagged the DNA in the virus with radioactive phosphorus.

• They tagged the proteins

in the virus with radioactive

sulfur.• Exposed tagged viruses to

bacterial cells

11

Bacterial cell

Therefore the function of DNA was determined as the genetic material responsible for heredity!

Hershey and Chase (1952) “confirm that DNA is the genetic material”

8.1 Identifying DNA as the Genetic Material

The DNA that makes up genes must be cable of…

• Storing Information: information for characteristics & patterns of development

• Copying Information: a cell copies its DNA before it divides

• Transmitting Information: genes are passed from one generation to the next

What is the role of DNA in heredity?