What is the difference between leading and lagging strands?

What is the difference between leading and lagging strands?

• A. The leading strand is synthesized discontinuously away from the fork; the lagging strand is synthesized continuously toward the fork.
• B. The leading strand is synthesized continuously toward the fork; the lagging strand is synthesized discontinuously toward the fork.
• C. The leading strand is synthesized continuously toward the fork; the lagging strand is synthesized discontinuously away from the fork as Okazaki fragments.
• D. Both strands are synthesized continuously toward the fork.

Answer: (C)

The main idea here is how DNA polymerase copies DNA directionally. DNA polymerase can only synthesize new DNA in the 5' to 3' direction. At the replication fork, one template runs 3' to 5' toward the fork, so it can be copied continuously in the same direction as the fork is opening—that’s the leading strand. The other template runs 5' to 3' toward the fork, so synthesis must occur in short segments moving away from the fork; these short pieces are called Okazaki fragments and are later stitched together to form a continuous strand—that’s the lagging strand. So the leading strand is synthesized continuously toward the fork, while the lagging strand is synthesized discontinuously away from the fork as Okazaki fragments.

The main idea here is how DNA polymerase copies DNA directionally. DNA polymerase can only synthesize new DNA in the 5' to 3' direction. At the replication fork, one template runs 3' to 5' toward the fork, so it can be copied continuously in the same direction as the fork is opening—that’s the leading strand. The other template runs 5' to 3' toward the fork, so synthesis must occur in short segments moving away from the fork; these short pieces are called Okazaki fragments and are later stitched together to form a continuous strand—that’s the lagging strand. So the leading strand is synthesized continuously toward the fork, while the lagging strand is synthesized discontinuously away from the fork as Okazaki fragments.