What describes the semiconservative model of DNA replication?

What describes the semiconservative model of DNA replication?

• A. Each new double helix consists of two newly formed strands.
• B. Each new double helix consists of one old parental strand and one newly formed daughter strand.
• C. Both strands are completely new.
• D. The original double helix remains intact and is copied once.

Answer: (B)

The main idea here is that DNA replication is semiconservative. That means each new double helix contains one strand that came from the original molecule and one newly synthesized strand. During replication, the double helix unwinds and each parental strand serves as a template for building a complementary new strand, so the old information is preserved in one strand of every daughter molecule. This description is the best fit because it captures how the parental strands guide exact copying of their sequences, producing two DNA molecules that each carry one old strand and one new strand. It’s also supported by classic experiments showing that after replication, daughter molecules are hybrids containing one original strand and one new strand. The other descriptions don’t match what is observed: having both strands be newly formed would produce two fully new duplexes, not one old and one new per molecule; saying both strands are completely new describes a fully new copy, which isn’t how cells replicate; and saying the original double helix remains intact and is copied once implies no separation or pairing with a new strand, which doesn’t fit the semiconservative mechanism.

The main idea here is that DNA replication is semiconservative. That means each new double helix contains one strand that came from the original molecule and one newly synthesized strand. During replication, the double helix unwinds and each parental strand serves as a template for building a complementary new strand, so the old information is preserved in one strand of every daughter molecule.

This description is the best fit because it captures how the parental strands guide exact copying of their sequences, producing two DNA molecules that each carry one old strand and one new strand. It’s also supported by classic experiments showing that after replication, daughter molecules are hybrids containing one original strand and one new strand.

The other descriptions don’t match what is observed: having both strands be newly formed would produce two fully new duplexes, not one old and one new per molecule; saying both strands are completely new describes a fully new copy, which isn’t how cells replicate; and saying the original double helix remains intact and is copied once implies no separation or pairing with a new strand, which doesn’t fit the semiconservative mechanism.