What does semiconservative replication mean?

What does semiconservative replication mean?

• A. One old and one new strand per molecule
• B. Both strands are new
• C. DNA is replicated twice per cell cycle
• D. Replication occurs only at origins

Answer: (A)

Semiconservative replication means each daughter DNA molecule contains one strand from the original molecule and one newly synthesized strand. As the double helix unwinds, each parental strand acts as a template for a new complementary strand, so two DNA molecules are produced, each with one old strand and one new strand. This pattern was famously demonstrated by Meselson and Stahl using isotope labeling, showing that after one round of replication every molecule comprised one conserved strand and one newly made strand. So the correct description is that there is one old strand and one new strand per molecule. The other options don’t describe this feature: having both strands new would mean no parental template is retained, replication twice per cell cycle describes timing rather than product composition, and replication only at origins concerns where replication starts rather than the nature of the copied strands.

Semiconservative replication means each daughter DNA molecule contains one strand from the original molecule and one newly synthesized strand. As the double helix unwinds, each parental strand acts as a template for a new complementary strand, so two DNA molecules are produced, each with one old strand and one new strand. This pattern was famously demonstrated by Meselson and Stahl using isotope labeling, showing that after one round of replication every molecule comprised one conserved strand and one newly made strand.

So the correct description is that there is one old strand and one new strand per molecule. The other options don’t describe this feature: having both strands new would mean no parental template is retained, replication twice per cell cycle describes timing rather than product composition, and replication only at origins concerns where replication starts rather than the nature of the copied strands.