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

B

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.