Meselson-Stahl Experiment Video Lessons

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Concept: Meselson-Stahl Experiment

Problem: To confirm the semiconservative model of replication, it was important for Meselson and Stahl to quantify the amount of DNA in each band produced by density-gradient centrifugation. To accomplish this, they took advantage of the fact that DNA absorbs ultraviolet light, and used UV light to photograph each tube. By scanning the UV photographs with a microdensitometer, graphs like the ones below were produced. The height of each peak in the graph is directly proportional to the concentration of DNA in the corresponding band. Also, the position of each peak reflects the 14N and 15N content of the band. Suppose that the scientists analyzed the same amount of DNA (10 units) by density-gradient centrifugation after two, three, and four rounds of replication in 14N medium. What would you predict the microdensitometer graph would look like after each round? The beginning of the experiment as well as Replication Cycle 1 is given to you. Match up replication rounds “A”, “B” and “C” in the correct order with Replication Cycles 2, 3 and 4.Match up replication rounds “A”, “B” and “C” in the correct order with Replication Cycles 2, 3 and 4.a) replication cycle 2 =b) replication cycle 3 =c) replication cycle 4 =

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Problem Details

To confirm the semiconservative model of replication, it was important for Meselson and Stahl to quantify the amount of DNA in each band produced by density-gradient centrifugation. To accomplish this, they took advantage of the fact that DNA absorbs ultraviolet light, and used UV light to photograph each tube. By scanning the UV photographs with a microdensitometer, graphs like the ones below were produced. The height of each peak in the graph is directly proportional to the concentration of DNA in the corresponding band. Also, the position of each peak reflects the 14N and 15N content of the band. Suppose that the scientists analyzed the same amount of DNA (10 units) by density-gradient centrifugation after two, three, and four rounds of replication in 14N medium. What would you predict the microdensitometer graph would look like after each round? The beginning of the experiment as well as Replication Cycle 1 is given to you. Match up replication rounds “A”, “B” and “C” in the correct order with Replication Cycles 2, 3 and 4.

Match up replication rounds “A”, “B” and “C” in the correct order with Replication Cycles 2, 3 and 4.

a) replication cycle 2 =

b) replication cycle 3 =

c) replication cycle 4 =

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Based on our data, we think this problem is relevant for Professor Waletzko's class at OSU.