Which statement best describes the composition of each newly formed DNA molecule after replication?

Which statement best describes the composition of each newly formed DNA molecule after replication?

• A. One old and one new
• B. Two old
• C. Two new
• D. One old and two new

Answer: (A)

In DNA replication, each new DNA molecule is formed semiconservatively: the two strands of the original double helix separate, and each original strand serves as a template for a new complementary strand. DNA polymerase builds the new strand using base pairing, so every daughter molecule ends up with one old (parent) strand and one newly synthesized strand. That’s why the best description is one old and one new strand in each new DNA molecule. The other possibilities don’t fit because a molecule cannot have two old strands (both would be parental, implying no replication), two new strands (no template used), or one old and two new strands (a DNA molecule has only two strands).

In DNA replication, each new DNA molecule is formed semiconservatively: the two strands of the original double helix separate, and each original strand serves as a template for a new complementary strand. DNA polymerase builds the new strand using base pairing, so every daughter molecule ends up with one old (parent) strand and one newly synthesized strand. That’s why the best description is one old and one new strand in each new DNA molecule.

The other possibilities don’t fit because a molecule cannot have two old strands (both would be parental, implying no replication), two new strands (no template used), or one old and two new strands (a DNA molecule has only two strands).