1. Chapter 9
Sections 9-1 and 9-2

2. Section 9-1 Identifying the Genetic Material
Mendel’s experiments and results answered why you resemble your parents – because you have copies of their chromosomes, which contain their genes
New Question – What are genes made of?

3. Griffith’s Experiments
Griffith, a bacteriologist, was trying to prepare a vaccine against the pneumonia-causing bacterium, Streptococcus pneumoniae
VACCINE – substance that is prepared from killed or weakened microorganisms and is introduced into the body against future infections by the microorganisms

4. There are two types/strains of S. pneumoniae
First Strain – enclosed in a capsule made of polysaccharides. Makes bacterium virulent (disease causing). Smooth in appearance. Known as the S strain.
Second Strain – no polysaccharide capsule. Does not cause disease. Rough in appearance. Known as the R strain.

5. Mice infected with the S strain die, and the mice infected with the R strain do not.
To determine if the capsule was what was causing the disease, Griffith designed an experiment with both strains of the bacterium.
Griffith first injected mice with dead S bacteria. The mice remained healthy.
He then injected mice with “heat-killed” S bacteria (capsule still in tact). Mice remained healthy.

6. This proved that the capsule did not cause the disease, but what did?
Griffith then mixed the R strain bacteria with the heat-killed S strain. What do you think happened?
The mice died.
Griffith examined the blood of those mice and found NO R strain bacteria. He only found S strain.
The R strain had acquired the capsule from the S strain, changed, and became virulent.

7. Griffith’s experiment allowed him to discover what is known as TRANSFORMATION – a change in phenotype caused when bacterial cells take up foreign genetic material.
Now… What causes transformation?

8. Avery’s Experiment
There was a series of experiments that demonstrated that protein-destroying enzymes did not stop the process of transformation, but DNA-destroying enzymes did stop it.
Avery and his colleagues showed that DNA is the material responsible for transformation.

9. Hershey and Chase’s Experiment
It was then known that viruses were made of DNA or RNA surrounded by a protein coat for protection.
Bacteriophage or Phage – a virus that infects only bacteria. When they infect bacteria, they produce more virus which is released when the bacterial cell ruptures.

10. Hershey and Chase used bacteriophage T2.
They knew the only place sulfur was found was in the protein coating of the phage, and they also knew that phosphorus was only found in the DNA.
They used these chemical differences to carry out the experiment.

11. Step One
They grew T2 with E. coli that contained radioactive sulfur and another batch grown in radioactive phosphorus.
As the phage grew, it would incorporate each of the radioactive compounds.
Step Two
The radioactive labeled phage was used to infect two separate batches of E. coli.
The radioactive material could be followed through the biological processes, and this would show what was being transferred into the bacteria.

12. Step Three
After a few minutes, they tore the radioactive labeled phage off the bacterial cells.
They then used a centrifuge to separate the bacteria and phages.
Upon examining the upper layer (phage material), they found most of the radioactive sulfur was still part of the phage.
The radioactive phosphorus was found in the bacterial cells.
This showed that the viral DNA had been injected into the bacteria.

13. Step Four/Conclusions
Hershey and Chase concluded that the DNA of viruses is injected into the bacterial cells, and most of the proteins remain outside the cell.
This showed that DNA was the hereditary material.

14. 9-1 Review
Griffith discovered transformation, which is a change in phenotype caused when bacterial cells take up foreign genetic material.
Hershey and Chase determined that DNA was the material that carries hereditary information.

15. Section 9-2 The Structure of DNA
Watson and Crick determined the structure of DNA.
DNA is a molecule that is a double helix – two strands twisted around each other, like a winding staircase.
Each strand is made of linked nucleotides (a 5 carbon sugar, a nitrogen base, and a phosphate group).

18. The 5 carbon sugar in DNA is deoxyribose.
There are four different nitrogen bases: Adenine, Cytosine, Thymine, and Guanine.
Adenine – A
Guanine – G
Thymine – T
Cytosine - C

19. PURINES: Made of two rings – adenine and guanine
PYRIMIDINES: Made of one ring – thymine and cytosine
Chargaff’s Discovery – The amount of adenine in a DNA molecule always equals the amount of thymine in the same molecule. This is the same for cytosine and guanine. The amount of both pairs found in each molecule of different organisms will vary.

20. Pyrimidines
Purines

21. Wilkins and Franklin – the first to use X-Ray diffraction to photograph DNA fibers. The pictures showed that DNA resembled a tightly coiled helix and was composed of two or three stands of linked nucleotides.
Watson and Crick – First to create the three-dimensional model of the DNA molecule.

22. DNA Base-Pairing Rules
A purine on one strand is always paired with a pyrimidine on the opposite strand.
ADENINE ALWAYS PAIRS WITH THYMINE!!! Forms two hydrogen bonds with each other.
GUANINE ALWAYS PAIRS WITH CYTOSINE!!! Forms three hydrogen bonds with each other.

23. DNA Base-Pairing Rules
The strictness of base-pairing results in two strands that are complementary to each other; that is, the sequence of bases on one strand determines the sequence on the other strand.
TCGAACT Original Strand
AGCTTGA Complementary Strand

27. DNA Base-Pairing Rules
Problem 1
AGCCTGACGGATTCCGAT
TCGGACTGCCTAAGGCTA
Problem 2
GCAATTGACCATGGAATCG
CGTTAACTGGTACCTTAGC

28. 9-2 Review http://www.biologycorner.com/bio4/notes/DNA-structure.php
DNA is a double helix made of two strands of linked nucleotides.
Purines – A and G and Pyrimidines – C and T
A always pairs with T AND c always pairs with G

29. HOMEWORK Section Review Questions p. 195 (1-5)
Active Reading Worksheets for 9-1 and
9-2