Question

The enzyme DNA polymerase works only in the 5′ to 3′ direction. How does this affect the leading strand and the lagging strand?

A. DNA polymerase can work on both the leading and the lagging strand but is much faster on the leading strand.
B. DNA polymerase can work continuously on the leading strand but works discontinuously on the lagging strand, creating Okazaki fragments.
C. DNA polymerase can use only the leading strand as a template. A different enzyme is used to synthesize DNA on the lagging strand.
D. DNA polymerase can work continuously on the leading strand but must flip the lagging strand around before it can work on it

Answer 1

DNA polymerase can only add nucleotides in the 5′ to 3′ direction, resulting in continuous synthesis of the leading strand and discontinuous, fragmented synthesis of the lagging strand known as Okazaki fragments.

Step-by-step explanation:

The enzyme DNA polymerase works only in the 5′ to 3′ direction during DNA replication. This specificity affects how both the leading and lagging strands are synthesized. The leading strand is synthesized continuously in the direction of the replication fork because it aligns with the directionality of DNA polymerase. However, the lagging strand is synthesized in a discontinuous manner away from the replication fork, resulting in short stretches of DNA called Okazaki fragments. These fragments are later joined to form a continuous strand by the action of DNA ligase. As such, the correct answer to how DNA polymerase affects the leading and lagging strand is option B: DNA polymerase can work continuously on the leading strand but works discontinuously on the lagging strand, creating Okazaki fragments.

Answer 2

B

Step-by-step explanation:

DNA replication is semiconservative- meaning the old template strand will form a double helix with the newly synthesized strand. The DNA polymerase can only replicate DNA in the 5’ -> 3’ direction on a DNA strand. However, because the two strands of a DNA double helix run antiparallel (and they are replicated together), then during replication, one strand will be oriented in the opposite direction (i.e 3’ -> 5’ direction).

Because DNA polymerase requires a primer to begin replication, the leading strand will require one primer, because replication on this strand occurs continuously. On the lagging strand, many primers are required because replication is done piecemeal forming fragments called Okazaki fragments. The fragments are later joined by DNA ligases.