Question

which of the following diagrams best represents leading strand and okazaki fragment synthesis at a replication fork? choose 1 answer: diagrams a, b, c, d as shown

Explanation:

To determine the correct diagram, we recall DNA replication: DNA polymerase synthesizes new strands only in the \(5'\to3'\) direction. The leading strand is synthesized continuously (in the direction of the replication fork movement), and the lagging strand (with Okazaki fragments) is synthesized discontinuously (opposite to the replication fork movement, as short fragments).

• The replication fork opens with one template strand having a \(3'\) end towards the fork (leading strand template) and the other with a \(5'\) end towards the fork (lagging strand template).
• The leading strand is synthesized continuously in the \(5'\to3'\) direction, following the fork. The lagging strand is synthesized as Okazaki fragments (each \(5'\to3'\)) in the opposite direction of the fork, so the arrows for the lagging strand should point backward relative to the fork’s movement, and the leading strand forward.

Looking at the options, Option B shows the leading strand (upper) synthesized in the direction of the fork (arrow towards the fork’s interior, \(5'\to3'\) along the template’s \(3'\) end) and the lagging strand (lower) with Okazaki fragments (arrows pointing opposite to the fork’s movement, as discontinuous synthesis). Other options have incorrect directionality (e.g., A has leading strand arrow opposite, C/D have lagging strand arrows in the wrong direction relative to the fork).

Answer:

B. The diagram where the leading strand (upper) is synthesized continuously in the direction of the replication fork (arrow towards the fork) and the lagging strand (lower) has Okazaki fragments with arrows pointing opposite to the fork’s movement (discontinuous synthesis), consistent with \(5'\to3'\) synthesis for both strands.