Deoxyribonucleic Acid (DNA) Students will be successful when they can…….. 1.When they can summarize the experiments leading to the discovery of DNA as the genetic material 2.Diagram and label the basic structure of DNA 3.Describe the basic structure of the eukaryotic chromosome

Discovering DNA The Fredrick Griffith Experiment (1928)

Griffith used two different strains of a bacteria that causes Pneumonia (Streptococcus pneumoniae) One strain had a sugar coat (the S strain), and caused pneumonia killing a mouse by injection. the other did not have a coat and is referred to as the rough strain (R strain). It did not kill the mouse by injection.

Griffith discovered that if he heated the S strain it would die, and no longer kill the mouse. But, if he mixed the heated S strained with some live R strain (non disease-causing) the R strain would be transformed into the S strain, killing the mouse. The Smooth strain was extracted from the dead mouse and cultured. It was still the rough strain, but had developed characteristics of the disease causing strain.

Griffith’s Conclusions Griffith concluded that there had been a transformation from the live R bacteria to Live S bacteria. This experiment set the stage for the search to identify the transforming substance.

Oswald Avery’s Experiment (1944) Avery and Colleagues identified the molecule that transformed the R strain of bacteria into the S strain. He isoladed different macromolecules, such as DNA, Protien, and lipids. When the live R strain was exposed to the DNA of the S strains DNA, it was transformed into the disease causing S strain.

Hershey and Chase Experiment (1952) Alfred Hershey and Martha Chase published results of experiments that provided definitive evidence that DNA is the transforming factor

The Experiment Hershey and Chase used a new technique called radioactive labeling using radio-active Phosphorus(P32) and Radioactive sulfur (S35). Proteins take up sulfur not phosphorus, so the proteins are labeled. DNA takes up Phosphorus, but not sulfur, therefore labeling the DNA.

Viruses and Bacteria are Grown in Medium Containing 32 P, and another group of Viruses are grown in a medium of 35 S. And then Blended up

The Blender dislodges the viruses from the bacteria cells, and the bacteria is seperated from the liquid containing the viruses.

Results of the Hershey Chase Experiment Results: bacterial cells infected with the radioactive label of 32 P had incorporated 32 P into its cells. The bacteria infected with the 35 S did not incorporate it into itself, the 35 S was left in the broth.

Conclusions DNA not Protein was the genetic material that could be passed from generation to generation in viruses.

II. DNA Structure After Hershey and Chase found that DNA was the molecule responsible for inheritance a scientific race had begun to discover the structure of the DNA molecule.

What is a Nucleotide The structure of Nucleotides includes: A phosphate sugar backbone, with one of the 5 nitrogenous bases (ATCG,U).

The 4 Nucleotide bases of DNA and Uracil (RNA) Uracil (only found in bacterial RNA)

We’ve seen this structure before!! (this is a molecular homology, and evidence for evolution)

The Brilliance of Erwin Chargaff (1950) Chargraff analyzed the numbers of each nucleotide (GCTA) in the entire genomes of different species. Here’s what he found!

Well, for starters it implies that the Adenine and Thymine are related some how, as well as Cytosine and Guanine? Like, maybe they’re totally complementary base pairs. DUDE!!!

Rosalind Franklin Rosalind Franklin took a new job at King’s college in London working with a technique called X-ray Diffraction. X-ray diffraction shoots X- rays at molecules and measure how the energy waves are broken up. Allowing photographs of molecules to be taken.

Photograph 51 Photograph 51 showed a pattern describing a double helix. This photograph along with other data was taken without her knowledge by her Mentor and shared with two other scienctists.

James Watson and Francis Crick Both were working at Cambridge University (London) when they saw Rosalind photograph. They soon realized that structure of the DNA was a double helix, and built their famous model.

The DNA Model that won them the Nobel Prize 1.Two outside strands consist of alternating deoxyribose and phosphates. 2.Cytosine and guanine bases pair to each other by three hydrogen bonds 3.Thymine and adenine bases pair to each other by two hydrogen bonds

Orientation of the Two Strands The top strand of DNA is the 5’ (5 prime) strand and at the end of the top rail is the 3’ (3 prime) and said to be 5’ to 3’ orientated. The bottom rail is the opposite, 3’ to 5’. This is referred to as antiparallel.

The Announcement In 1953 Watson and Crick surprised the scientific community by publishing a one-page paper in the journal Nature suggesting a structure for the DNA molecule as well as a hypothesized a method of replication.