Download Bell Work: What does DNA stand for?

Bell Work:
What does DNA stand for?
Welcome back, while you are working I will check your questions for the first page of the science fair packet.
Glowing Mouse?
The mouse is glowing because of green fluorescent protein (GFP). This gene was extracted from a glowing jellyfish, put into a virus and then into a mouse egg. The jellyfish gene was incorporated into the mouse's gene and TADA you have a glowing mouse!
Why the heck do we need glowing mice? So, it is easier for cats to catch??
No, researchers hope to be able to track cancer cells by using the GFP gene.
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Griffith's Mice
In 1928 microbiologist Frederick Griffith was investigating two forms of the bacterium that causes pneumonia.
Form 1 (S bacteria) was surrounded by a coating made from sugar molecules.
Form 2 (R bacteria) did have the smooth coating.
When he injected the mice, only those with S bacteria died. If the S bacteria were killed by heating, the mice were unaffected.
When he injected them with a combination of heat­killed S bacteria and R bacteria, the mice surprisingly died.
Even more surprising was that he found live S bacteria in the blood samples from the dead mice.
He concluded that some material had been transferred from the heat­killed S bacteria to the live R bacteria. This material changed harmless R bacteria into disease causing S bacteria. This material was called "the transforming principle"
Oswald Avery wanted to find out exactly what the material Griffith found was.
He began a series of tests with R and S bacteria.
They ran a series of tests to determine if it was DNA or protein was the transforming principle.
Chemical tests showed no proteins were present, but DNA was.
Chemical analysis showed the proportions of the elements found was very similar to DNA, and proteins contain almost no phosphorus.
Enzyme tests proved there was no protein, because when the team added enzymes that break down proteins, the transforming of R to S bacteria still occurred.
They concluded that DNA must be the transforming principle.
Yet, there will still scientists that insisted Avery's extract had proteins in it. Apparently these were the scientists who couldn't read.
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In 1952 Alfred Hershey and Martha Chase had conclusive evidence that DNA was the transforming principle.
They were studying bacteriophages, which are a type of virus that infect bacteria. These bacteria were great to use because they are pretty much DNA surrounded by a protein coat.
Hershey and Chase realized that protein contains sulfur, but very little phosphorus and DNA contains phosphorus, but no sulfur. So, they grew phages that contained radioactive isotopes of sulfur and phosphorus.
Experiment 1­ Bacteria where infected with phages that had radioactive sulfur atoms in their protein. They then used a blender, to separate the bacteria from the phages that remained outside the bacteria. None of them showed evidence of radioactivity.
Experiment 2­ Bacteria tagged with radioactive phosphorus were put through the same test. This time radioactivity was clearly present.
Finally this convinced scientists that the genetic material is DNA and NOT protein. They probably listened because they were American.
Edwin Chargaff
Analyzed the DNA of several different organisms and found the same four bases were found in all organisms.
But the proportion of these bases differed from organism to organism.
He did find the amount of adenine was equal to the amount of thymine and the amount of guanine was equal to the amount of cytosine.
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James Watson and Francis Crick were supposed to be studying the structure of proteins, but were fascinated by the structure of DNA. They hypothesized using the work of Hershey, Chase, Chargaff and Linus Pauling who said DNA was either a helix or a spiral, that DNA was a spiral.
At the same time Rosalind Franklin and Maurice Wilkins were studying DNA using x­ray crystallography.
The DNA is bombarded with radiation and a film captures the diffraction pattern.
Franklin's X­ray patterns showed an X surrounded by a circle, this data gave Watson and Crick the information they needed.
However, she didn't give it to them. Wilkins took the pictures to Watson and Crick, within weeks they had figured out the structure of DNA.
Wilkins, Watson and Crick won the Nobel Prize in 1962. Rosalind Franklin was not even mentioned and had died of cancer fours years early. However, a Nobel Prize cannot be awarded posthumously.
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