A-LevelBiologyNucleic acids and protein synthesis9700/12 · Oct/Nov 2011 · Q231 Mark
Bacteria were grown in a medium containing 15N. After several generations, all bacteria contained 15N. Some of these bacteria were transferred to a medium containing the isotope of nitrogen, 14N. The bacteria were allowed to divide once. The DNA of some bacteria was extracted and analysed. This DNA was all hybrid DNA containing equal amounts of 14N and 15N. Some bacteria from the medium with 15N were transferred into a medium of 14N. The bacteria were allowed to divide twice. The graph shows the percentages of 14N and 15N in the DNA of these bacteria. [Figure 23.1] Some bacteria from the medium with 15N were transferred into a medium of 14N. The bacteria were allowed to divide three times. What would be the percentages of 14N and 15N in the DNA extracted from these bacteria?
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
ABar chart showing 0% for 14N and 100% for 14N/15N
BBar chart showing 50% for 14N and 50% for 14N/15N
CBar chart showing 75% for 14N and 25% for 14N/15N
DBar chart showing 25% for 14N and 75% for 14N/15N
✓ Correct answer
C: Bar chart showing 75% for 14N and 25% for 14N/15N
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