Which DNA strand is synthesized discontinuously?

Which DNA strand is synthesized discontinuously?

• A. Leading strand
• B. Lagging strand
• C. Template strand
• D. Coding strand

Answer: (B)

The question tests how DNA is copied in replication. DNA polymerase only adds nucleotides in the 5′ to 3′ direction, so the strand running 3′ to 5′ toward the fork can be copied continuously as the fork opens—that’s the leading strand. The other parental strand runs 5′ to 3′ toward the fork, so synthesis must proceed away from the fork in short segments (Okazaki fragments) that are later stitched together; this is the lagging strand, synthesized discontinuously. The terms “template strand” and “coding strand” relate to transcription terminology and aren’t describing the replication-as-synthesis pattern here. So the strand synthesized discontinuously is the lagging strand.

The question tests how DNA is copied in replication. DNA polymerase only adds nucleotides in the 5′ to 3′ direction, so the strand running 3′ to 5′ toward the fork can be copied continuously as the fork opens—that’s the leading strand. The other parental strand runs 5′ to 3′ toward the fork, so synthesis must proceed away from the fork in short segments (Okazaki fragments) that are later stitched together; this is the lagging strand, synthesized discontinuously. The terms “template strand” and “coding strand” relate to transcription terminology and aren’t describing the replication-as-synthesis pattern here. So the strand synthesized discontinuously is the lagging strand.