The Meselson-Stahl Experiment

The Meselson and Stahl experiment provided evidence for which model of DNA replication?

• A) Conservative replication

• B) Dispersive replication

• C) Semi-conservative replication

• D) None of the above

Answer explanation

Explanation: The Meselson and Stahl experiment demonstrated that DNA replicates semi-conservatively, where each new DNA molecule consists of one old strand (template) and one newly synthesized strand. This finding supported the semi-conservative model of DNA replication proposed by James Watson and Francis Crick.

In the Meselson and Stahl experiment, what did the results confirm about DNA replication?

• A) Conservative replication, where both parent strands stay intact and serve as templates for new strands.

• B) Dispersive replication, where the parent strands are broken into fragments, and those fragments serve as templates for new strands.

• C) Semi-conservative replication, where the two parent strands serve as the template for the synthesis of new strands.

• D) None of the above.

Answer explanation

The Meselson and Stahl experiment provided strong evidence supporting the semi-conservative model of DNA replication, where each new DNA molecule contains one strand from the original DNA molecule and one newly synthesized strand. This confirms option C.

In the Meselson and Stahl experiment, bacterial cells were grown for several generations on a medium containing a heavy isotope of nitrogen. Which heavy isotope of nitrogen was used in this experiment?

• A) Nitrogen-13 (N-13)

• B) Nitrogen-14 (N-14)

• C) Nitrogen-15 (N-15)

• D) Nitrogen-16 (N-16)

In the Meselson and Stahl experiment, after the initial growth in a medium containing a heavy isotope of nitrogen (N-15), the bacterial cells were transferred to a new medium containing the normal lighter isotope, N-14. What was the purpose of this transfer?

• A) To label the newly synthesized DNA strands with N-15.

• B) To label the newly synthesized DNA strands with N-14.

• C) To distinguish between the two parental DNA strands.

• D) To observe the dispersion of nitrogen isotopes within the DNA molecules.

In the Meselson and Stahl experiment, after transferring bacterial samples to a medium containing N-14, the DNA was extracted and dissolved in a solution of cesium chloride. What was the purpose of dissolving the DNA in cesium chloride?

• A) To separate DNA into its individual nucleotide components.

• B) To visualize DNA under a microscope.

• C) To measure the density of DNA molecules.

• D) To break the DNA strands into smaller fragments for analysis.