Which model describes DNA replication where each new double helix consists of one original strand and one newly synthesized strand?

Which model describes DNA replication where each new double helix consists of one original strand and one newly synthesized strand?

• A. Conservative
• B. Dispersive
• C. Semiconservative
• D. Conjugative

Answer: (C)

DNA replication that preserves one original strand in each new double helix is semiconservative replication. In this mode, the two parental DNA strands separate, and each strand serves as a template for synthesizing a new complementary strand. The result is two DNA molecules, each composed of one old (parental) strand and one newly synthesized strand. This pattern was supported by the Meselson-Stahl experiment: after one replication round, the DNA population had intermediate density consistent with one old and one new strand per molecule; after a second round, both intermediate and light densities appeared as predicted for semiconservative replication. Conservative replication would yield one molecule with both original strands and another with both new strands, which isn’t what’s observed. Dispersive replication would produce mixtures where both strands of each molecule contain a patchwork of old and new DNA, also not matching the data. Conjugative refers to transfer of DNA between cells, not a replication mechanism. So the semiconservative model best explains how each new double helix ends up with one original strand and one newly made strand.

DNA replication that preserves one original strand in each new double helix is semiconservative replication. In this mode, the two parental DNA strands separate, and each strand serves as a template for synthesizing a new complementary strand. The result is two DNA molecules, each composed of one old (parental) strand and one newly synthesized strand. This pattern was supported by the Meselson-Stahl experiment: after one replication round, the DNA population had intermediate density consistent with one old and one new strand per molecule; after a second round, both intermediate and light densities appeared as predicted for semiconservative replication.

Conservative replication would yield one molecule with both original strands and another with both new strands, which isn’t what’s observed. Dispersive replication would produce mixtures where both strands of each molecule contain a patchwork of old and new DNA, also not matching the data. Conjugative refers to transfer of DNA between cells, not a replication mechanism. So the semiconservative model best explains how each new double helix ends up with one original strand and one newly made strand.