1. Identifying Substances of Genes
Chapter 12: DNA
Identifying Substances of Genes

2. Bacterial Transformation
Frederick Griffith ( )
British Scientist
Wanted to know what genes were made up of
Focused on Bacteria Pneumonia found in mice
2 strands: (S strain was deadly; R strand was harmless)
Ran a number of tests resulting in either live or dead mice
Surprised that a mixture of heat killed S strain and live R strain killed mouse
Gave him the idea of Transformation

3. Bacterial Transformation
What is Transformation?
Process of a gene changing the structure of bacteria from one strand to another
Oswald Avery ( )
American
Conducts experiment in 1944
Ran the bacteria against all types of substances
Transformation occurred
However, when they ran an experiment to destroy the DNA, transformation did not occur

4. Bacterial Viruses Alfred Hershey and Martha Chase
Wanted to determine if DNA or protein was genetic code
Used a bacteriophage to run the experiment
1952:
Which part of virus entered the cell? DNA or protein coat?
Understood that one of the them entered into the cell
Radioactive tags given to both protein and DNA
After separation, they found that DNA was molecule of heredity

5. Role of DNA Storing Information Copying Information
Controls blood type, eye color, and patterns of development
Copying Information
Needed for process of cell division
Transmitting Information
Used for when info is passed from parent to offspring

6. Chapter 12: DNA
Structure of DNA

7. Components of DNA Nucleic Acids Nucleotides
Molecules found in the cell’s nucleus
Nucleotides
Structure of DNA
Consists of:
Nitrogen base (Adenine, Thymine, Guanine, Cytosine)
5 carbon sugar (Deoxyribose)
Phosphate group
Covalent bonds are created between the sugar and phosphate group

8. Solving the Structure Chargaff’s Rule Erwin Chargaff (1905-2002)
Austrian looking to figure out how DNA was structured
Noticed proportions of nitrogen bases were similar
Adenine appeared 29.3%
Cytosine appeared 20%
Guanine appeared 20.7%
Thymine appeared 30%
Adenine always goes with Thymine
Cytosine always goes with Guanine
All DNA has this

9. Solving the Structure Rosalind Franklin (1920-1958)
Used x-ray defraction to help piece together part of structure
X-rays hit a crystal in the middle of the space
Causes light to shoot around object giving its shape
Showed that DNA strands twisted around each other (helix)
Showed it was made up of 2 strands
Franklin would ultimately die at age 37 due to overexposure to radiation from x-rays

10. Solving the Structure James Watson and Francis Crick
Watson (1928-) and Crick ( )
Came up with the idea of the double helix structure
Anti-parallel strands
Twist around each other in opposite directions
Bonds form between Adenine and Thymine; Cytosine and Guanine
Everything held together by hydrogen bonds
Durable enough to hold together but weak enough to allow flexibility and the strands to break apart during reproduction

11. Double Helix