Suppose you are a biologist trying to discover the process by which DNA copies itself. You grow cells in a culture that contains a special isotope of nitrogen, N-15, which will become part of any new DNA the cell makes. After one generation, you analyze
the DNA and find all the DNA has some N-15 in it. You then take those cells and grow them for another generation in a culture with the normal isotope of nitrogen, N-14, and find that half of the DNA has some N-15 in it and half of it has only N-14. From this information, what can you infer is the process by which DNA replicates?
What will be an ideal response?
The process must be that each strand of a double helix serves as the template for the synthesis of a new strand. After the first generation, all new DNA will have one strand that is new and one that is old, so each double helix will have one strand that has N-15 and one strand that does not. If those same cells are grown for another generation in N-14, each parent strand with N-15 will be paired up with a new strand that has just N-14, and each parent strand with just N-14 will be paired up with a new strand that also is just N-14. This explains why half of the new DNA in the second generation has N-15 and half has only N-14.
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deficiency.
a. phosphorus b. magnesium c. potassium d. oxygen e. nitrogen
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Indicate whether the statement is true or false
How were nitroglycerine's therapeutic benefits discovered?
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