Question

dna replication
learning objective 19.1: use a drawing that you create to explain the statement: \a newly synthesized dna strand is half old and half new.\

why is dna replication described as \semi - conservative?\

after replication completes, each double helix is made of one old strand and one new strand.

during dna replication, the common base - pairing rules (a with t, g with c) are only partially followed.

after replication completes, the dna double - helices are identical in some places and different in others.

during dna replication, only one strand is used as a template for new dna synthesis.

Explanation:

To determine why DNA replication is semi - conservative, we analyze each option:

• Option 1: In semi - conservative DNA replication, the original DNA double helix unwinds, and each of the old strands serves as a template for the synthesis of a new complementary strand. So, after replication, each new double helix consists of one old (template) strand and one newly synthesized strand. This matches the definition of semi - conservative replication.
• Option 2: Base - pairing rules (A - T, G - C) are strictly followed during DNA replication. So this option is incorrect.
• Option 3: After DNA replication, the new DNA double - helices are identical to the original (and to each other) in terms of genetic information, not "identical in some places and different in others". So this option is wrong.
• Option 4: During DNA replication, both strands of the double helix are used as templates for the synthesis of new strands, not just one. So this option is incorrect.

Answer:

A. After replication completes, each double helix is made of one old strand and one new strand.