What does semiconservative replication mean?

• A. Each daughter molecule contains two newly synthesized strands
• B. Both daughter molecules contain the original parent strands intact
• C. Replication occurs in only one direction
• D. Each daughter DNA molecule contains one parental strand and one newly synthesized strand

Answer: (D)

Semiconservative replication means that each daughter DNA molecule contains one parental (old) strand and one newly synthesized strand. During replication, the two strands of the original double helix unwind and separate, with each old strand serving as a template for a new complementary strand. DNA polymerases add nucleotides in the 5' to 3' direction, pairing A with T and G with C, so two new double helices form, each built from one old strand and one new strand. This outcome is supported by classic experiments showing that the parental strands persist in the daughters. The other ideas would imply both daughter molecules keep the original strands intact or both strands are new, or they focus on directionality rather than the old-versus-new strand pairing.