DNA replication is semiconservative. Which statement describes this mode?

DNA replication is semiconservative. Which statement describes this mode?

• A. Each daughter DNA molecule contains two old strands
• B. Each daughter DNA molecule contains two new strands
• C. Neither strand is retained
• D. Each daughter DNA molecule contains one old strand and one new strand

Answer: (D)

Semiconservative replication means each new DNA molecule contains one old (parental) strand and one newly synthesized strand. During replication, the two strands separate and each serves as a template for a new complementarily paired strand. DNA polymerase adds nucleotides in the 5' to 3' direction against the template, so the new strand is built to match the old one. As a result, you end up with two daughter molecules, each with one old strand and one new strand. The descriptions that imagine both strands being old or both being new would not reflect how the parental strands are used as templates and how the new strands are synthesized. Historically, experiments like Meselson and Stahl’s supported this one-old-one-new model.

Semiconservative replication means each new DNA molecule contains one old (parental) strand and one newly synthesized strand. During replication, the two strands separate and each serves as a template for a new complementarily paired strand. DNA polymerase adds nucleotides in the 5' to 3' direction against the template, so the new strand is built to match the old one. As a result, you end up with two daughter molecules, each with one old strand and one new strand. The descriptions that imagine both strands being old or both being new would not reflect how the parental strands are used as templates and how the new strands are synthesized. Historically, experiments like Meselson and Stahl’s supported this one-old-one-new model.