A-LevelBiologyNucleic acids and protein synthesis9700/12 · Oct/Nov 2010 · Q211 Mark
A culture of bacteria had all its DNA labelled with the heavy isotope of nitrogen (15N). A sample was taken and spun in a centrifuge. The diagram shows the position of the DNA band at Z in the centrifuge tube. [Figure 21.1 showing a centrifuge tube with bands labeled X, Y, Z] The culture was then allowed to reproduce using nucleotides containing the normal isotope of nitrogen (14N). Samples were taken and spun in a centrifuge after one generation and again after two generations. In which pattern would the DNA be found after the first and after the second generations? after first generation after second generation
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.
Ahalf at X and half at Y quarter at X, quarter at Z and half at Y
Bhalf at X and half at Z quarter at X, quarter at Z and half at Y
Call at Y half at X and half at Y
Dall at Z half at Y and half at Z
✓ Correct answer
C: all at Y half at X and half at Y
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