Which statement best identifies the strand that is synthesized continuously toward the replication fork during DNA replication?

Which statement best identifies the strand that is synthesized continuously toward the replication fork during DNA replication?

• A. The strand synthesized discontinuously toward the replication fork
• B. The strand synthesized continuously away from the replication fork
• C. The strand synthesized discontinuously away from the replication fork
• D. The strand synthesized continuously toward the replication fork

Answer: (D)

DNA polymerases can only synthesize new DNA in the 5' to 3' direction. As the replication fork opens, the template strand oriented 3' to 5' toward the fork allows continuous synthesis because the polymerase can add nucleotides in the direction of fork movement. This is the leading strand. The opposite template runs 5' to 3' toward the fork, so synthesis must occur in short segments away from the fork (Okazaki fragments) and later be joined. So describing the strand that is synthesized continuously toward the replication fork correctly identifies the leading strand.

DNA polymerases can only synthesize new DNA in the 5' to 3' direction. As the replication fork opens, the template strand oriented 3' to 5' toward the fork allows continuous synthesis because the polymerase can add nucleotides in the direction of fork movement. This is the leading strand. The opposite template runs 5' to 3' toward the fork, so synthesis must occur in short segments away from the fork (Okazaki fragments) and later be joined. So describing the strand that is synthesized continuously toward the replication fork correctly identifies the leading strand.