3.9 - The Experimental Proof

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Across
  1. 3. The result was that 15N was .................. into newly synthesised DNA.
  2. 7. They grew E. coli in a medium containing 15NH4Cl (15N is the ......... isotope of nitrogen) as the only nitrogen source for many generations.
  3. 9. Then they ............. the cells into a medium with normal 14NH4Cl and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as double- stranded helices.
  4. 10. This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a .............. density gradient.
  5. 12. It was shown first in ........... and subsequently in higher organisms, such as plants and human cells.
Down
  1. 1. Matthew .......... and Franklin ......... performed the experiment in 1958:
  2. 2. Thus, the DNA that was extracted from the culture one generation after the transfer from 15N to 14N medium [that is after 20 minutes; E. coli divides in 20 minutes] had a ........ or ......... density.
  3. 4. It is now proven that DNA ...........semi-conservatively.
  4. 5. The various samples were separated independently on CsCl gradients to measure the .......... of DNA.
  5. 6. The experiments proved that the DNA in ........... also replicate semi-conservatively.
  6. 8. DNA extracted from the culture after another generation [that is after 40 minutes, II generation] was composed of equal amounts of this ......... DNA and of ‘..........’ DNA.
  7. 11. Very similar experiments involving use of radioactive thymidine to detect distribution of newly synthesised DNA in the chromosomes was performed on Vicia faba (faba beans) by ........... and colleagues in 1958.