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Activity 16.1 Concept map

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Brielle Cameron

on 24 February 2011

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Transcript of Activity 16.1 Concept map

Map A Griffith's Experiment Mouse 1 Injected with Living S (Steptococcus) cells The Control Mouse Dies... Mouse 2 The Control Injected with Living R (Strotococcus0) Cells Mouse Lives! Mouse 3 The Control Injected with Heat- Killed S Cells Mouse Lives! Mouse 4 The Experimental Injected with a mixture of heat-killed S cells and living R cells Mouse Dies... This mouse died because the living R cells went through a... Transformation. (a change in genotype and phenotype due to the assimilation of external DNA by a cell.) This means that even though the S cells were heat killed, its DNA was not, which helped transform the R cells into S cells by changing its DNA. This allowed the R cells to change to S cells and reproduce more S cells. Because of this experiment, this helped Oswald Avery (an American bacteriologist), and his colleagues, Maclyn McCarty and Colin Macleod to find the identity of the transforming substance. They focused on three main substances: RNA, protein, and DNA By breaking open heat-killed pathogenic bacteria and extracting the cellular contents (in separate samples using RNA, proteins and DNA) that activated either RNA, proteins, or DNA, they found that... That when DNA was kept active (and only DNA) is when transformation occured. But this did not occur with RNA or DNA. Map B Hershey and Chase's Experiment Using a bacteria called T2 (a bacteriophage or phage), which is mainly main of protein and DNA, Hershey and Chase were able to find out which of the two is involved in the process of turning E. coli in to a reprodcution center for more T2. By labeling proteins with a radioactive sulfur (35 S) and DNA with a radioactive phosphorus (32 P), Hershey and Chase were able to track where both proteins and DNA in the phage went to. First, they put the phases through a waring blender, after the phages infected the bacteria, and this process helped separate the phases from the now infected bacteria. Then they put the mixture through a high-velocity centrifugation so the bacteria would form a pellet at the bottom of the test tube and the phages would sit at the top because they are lighter. They found that DNA was responsible for T2's ablility to turn E. coli into reproducing viruses, not protein, since DNA was seen traveling in to the E. coli and not protein. Map C Watson and Cricks Discovery By looking at a X-ray Diffraction photo of DNA that Rosaling Frankin took, Watson and Crick were able to make up the shape of DNA, the double helix. By using Chargaff's rule.... Which is the equivalences for any given species between the number of A and T bases and the number of G adn C bases, Watson and Crick began to find out even more about DNA's stucture. They found out the purine stucture: asenine and guanine (A and G) And the pyrimidine structure: cytosine and thymine (C and T) They knew that two purines put together would be to wide to fit into the double helix structure and that two pyrimidines would be to narrow to fit into the double helix structure. So, this had to mean that one purine and one pyrimidine would be just perfect for the double helix part (sounds like Goldylocks, doesn't it?) Next was to figure out which puzzel piece fit with which... They knew that hydrogen bonds would have to be used to keep the structure of DNA because it is strong but also easily breakable, which allows it to be copied so easily. Going off this information, they then found out that only adenine formed a hydrogen bond with thymine (and visa versa), while guanine only formed a hydrogen bond with cytosine (and visa versa). This is what they came up with... Also, by reading Rosaling Franklin's unpublished annual report summary, Waston and Crick found out that a sugar-phosphate backbone was on the outside of the double helix structure. Map D Meselson and Stahl's Experiment Basically, Watson and Crick "barrowed" information from other scientists in order to find the structure of DNA and become famous. So! How does DNA relicate itself so it can pass on genitic information to the next generation? First, three models were created that could answer this question... Conservative Model When two parental strands reassociate after acting as templates for new strands. This then restores the parental double helix Semiconservative model When two strands of the parental molecule separate and each functions as a template for synthesis of a new to make a complementary strand. Dispersive Model When each strand of both daughter molecules contains a mixture of old and newly synthesdized DNA. After having a model, Meselson and Stahl went to work to find out which model is the right model. First, they cultured E. coli in 15 N, which is a heavy isotope. Then they transferred the bacteria to 14 N, which is a lighter isotope. Then two DNA samples were taken from the 14 N flask (one every 20 minutes and one every 40 minutes, after the first and second replications). This allowed Meselson and Stahl could distingusih DNA of different densities by centriuging DNA extracted from the bacteria. They came to the conclustion that DNA replication is semiconservative. The End!
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