Multiple models were proposed to explain replication. What experimental approach allowed researchers to distinguish between them?
A. Cells were pulsed with high specific activity [3H] thymidine to show the direction of DNA synthesis on the chromosome.
B. Cells infected with T4 bacteriophage were grown in the presence of radioactive nucleotides. When DNA was analyzed in alkaline CsCl gradients, the presence of short DNA fragments indicated that discontinuous replication had occurred.
C. Bacteria were grown on 15NH4 until the entire DNA contained heavy nitrogen and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.
D. Bacteria were grown on [3H] thymidine until the entire DNA contained heavy thymidine and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.
E. None of these choices is correct.
C
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