What is the lagging strand?

• A. The new strand built away from the replication fork in pieces called Okazaki fragments
• B. The strand synthesized continuously toward the fork
• C. The template strand used for synthesis
• D. The RNA primer that initiates synthesis

Answer: (A)

The lagging strand is the newly synthesized DNA strand that is built in short pieces away from the replication fork. DNA polymerase can only add nucleotides in the 5' to 3' direction, so on the strand oriented 3' to 5' relative to the fork, synthesis occurs discontinuously. These short segments are called Okazaki fragments, each starting with an RNA primer laid down by primase. The fragments are later extended by DNA polymerase and finally joined together by DNA ligase after the RNA primers are removed and replaced with DNA. This contrasts with the leading strand, which is synthesized continuously toward the fork, and with the template strand or the primer, which are parts of the process but not the entire lagging strand itself.