Question

which of the following statements correctly describes how the leading and the lagging strands of dna formed during dna replication differ?

the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

the leading strand is synthesized by adding nucleotides to the 3 end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5 end.

the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together.

the leading strand is synthesized at twice the rate of the lagging strand.

Explanation:

1. Analyze the first option: DNA replication occurs with the replication fork moving. The leading strand is synthesized continuously in the 5' to 3' direction, which is the same as the replication fork's movement. The lagging strand is synthesized in the opposite direction of the replication fork (since it's also 5' to 3' but the fork moves, so it's made in Okazaki fragments), so this option's description of direction relative to the fork is correct.
2. Analyze the second option: Both leading and lagging strands are synthesized by adding nucleotides to the 3' end (DNA polymerase can only add to 3' end), so this option is wrong.
3. Analyze the third option: The leading strand is synthesized continuously, and the lagging strand is synthesized in short fragments (Okazaki fragments) that are later joined. This option has them reversed, so it's wrong.
4. Analyze the fourth option: There's no evidence that the leading strand is synthesized at twice the rate of the lagging strand; they are synthesized in coordination, so this option is wrong.

Answer:

A. The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.