Which model of DNA replication is accepted?

Which model of DNA replication is accepted?

• A. Conservative model
• B. Random replication model
• C. Dispersive model
• D. Semiconservative model

Answer: (D)

The concept being tested is how DNA strands are copied during replication. The accepted model is semiconservative, meaning each daughter DNA molecule ends up with one strand from the original molecule and one newly synthesized strand. This idea was solidified by the Meselson–Stahl experiments. They grew bacteria in heavy nitrogen so all DNA was heavy, then switched to light nitrogen and tracked DNA density. After one round of replication, every DNA molecule showed an intermediate density, indicating each molecule contained one old (heavy) strand and one new (light) strand. After a second round, the pattern split into two bands: some molecules remained intermediate while others were light, consistent with daughter molecules containing either one old and one new strand or two new strands. This outcome fits semiconservative replication and does not fit a purely Conservative model, which would produce one heavy and one light molecule after the first round, nor a purely Dispersive model, which would not yield two distinct bands after two generations.

The concept being tested is how DNA strands are copied during replication. The accepted model is semiconservative, meaning each daughter DNA molecule ends up with one strand from the original molecule and one newly synthesized strand.

This idea was solidified by the Meselson–Stahl experiments. They grew bacteria in heavy nitrogen so all DNA was heavy, then switched to light nitrogen and tracked DNA density. After one round of replication, every DNA molecule showed an intermediate density, indicating each molecule contained one old (heavy) strand and one new (light) strand. After a second round, the pattern split into two bands: some molecules remained intermediate while others were light, consistent with daughter molecules containing either one old and one new strand or two new strands. This outcome fits semiconservative replication and does not fit a purely Conservative model, which would produce one heavy and one light molecule after the first round, nor a purely Dispersive model, which would not yield two distinct bands after two generations.