During DNA replication, the leading strand is best described as which of the following?

• A. Synthesized 5' to 3' toward the fork
• B. Synthesized 3' to 5' away from the fork
• C. Made in short fragments called Okazaki fragments
• D. Requires RNA primers to start each fragment

Answer: (A)

The main idea here is that DNA polymerases add nucleotides only to the 3' end, so new DNA grows in the 5' to 3' direction. At the replication fork, the template strand that runs 3' to 5' toward the fork allows continuous synthesis toward the fork, producing a leading strand. This continuous, forward synthesis in the 5' to 3' direction toward the fork is what makes the leading strand best described as such. In contrast, the lagging strand runs opposite, so it’s made away from the fork in short Okazaki fragments, each needing a new RNA primer to start, which is why that description fits the lagging strand.