In semiconservative replication, what is the relationship between the two strands in each daughter DNA molecule?

In semiconservative replication, what is the relationship between the two strands in each daughter DNA molecule?

• A. Each daughter molecule contains one old strand and one newly synthesized strand
• B. Both strands are newly synthesized
• C. Both strands are parental
• D. No parental strands remain

Answer: (A)

Semiconservative replication means each daughter DNA molecule keeps one of the original parental strands and assembles a new complementary strand for it. As the double helix unwinds, each old strand serves as a template for a new strand, so after replication you get two DNA molecules, each with one old strand and one new strand. This happens because DNA polymerase can only add nucleotides onto an existing strand in a 5' to 3' direction, using the template to build a new complementary strand. The alternatives would require both strands to be new, both to be old, or a mix that doesn’t reflect how replication uses templates, none of which describe what actually occurs. So the two strands in each daughter molecule are one parental and one newly synthesized strand.

Semiconservative replication means each daughter DNA molecule keeps one of the original parental strands and assembles a new complementary strand for it. As the double helix unwinds, each old strand serves as a template for a new strand, so after replication you get two DNA molecules, each with one old strand and one new strand. This happens because DNA polymerase can only add nucleotides onto an existing strand in a 5' to 3' direction, using the template to build a new complementary strand. The alternatives would require both strands to be new, both to be old, or a mix that doesn’t reflect how replication uses templates, none of which describe what actually occurs. So the two strands in each daughter molecule are one parental and one newly synthesized strand.