1. 12.1 Identifying the Substance of Genes
Chapter12 DNA
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?
Vocabulary:
Transformation
bacteriophage

2. Warm-up
What is DNA?
A large molecule found in the nucleus of cells that is responsible for heredity (passing of genes from parent to offspring).
Gene: Sequence of DNA that codes for a protein and thus determines a trait; factor that is passed from parent to offspring
How do we know the function of DNA?
DNA was identified as the genetic material responsible for heredity through a series of experiments.

3. Rosalind Franklin 1952 Watson and Crick 1953
The discovery of DNA
Rosalind Franklin 1952 Watson and Crick 1953
Franklin
Rosalind Franklin determined what elements made up DNA (N & P)
Watson and Crick used Franklin’s data to describe the shape of DNA as a double helix
Watson
Crick
Double Helix

4. 12.1 Identifying the Substance of Genes
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

5. How do we know the function of DNA?
KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

6. Griffith (1924-41): finds “transforming material” (genetic material)11
What clues did bacterial transformation yield about the gene?
Griffith ( ): 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).
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.
Why?
But why did they die?

7. Griffith didn’t know what made up genes so…11
What clues did bacterial transformation yield about the gene?
Griffith didn’t know what made up genes so…
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.

8. What clues did bacterial transformation yield about the gene?11
What clues did bacterial transformation yield about the gene?
Avery’s Data
Avery’s Conclusion:
Chemical tests showed the chemical make-up of the unknown transforming samples matched that of DNA.

9. What role did bacterial viruses play in identifying genetic material?
Hershey and Chase
Used Viruses that infect bacteria called… Bacteriophages
A bacteriophage is a kind of virus that infects bacteria

10. Hershey and Chase (1952) “confirm that DNA is the genetic material”11
Hershey and Chase studied viruses that infect bacteria (bacteriophages)
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
Bacterial cell
Results - Tagged DNA was found inside the bacteria; tagged proteins were not!
Therefore the function of DNA was determined as the genetic material responsible for heredity!

11. The DNA that makes up genes must be cable of…
What is the role of DNA in heredity?
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