Question

The strand of parental DNA on which a new continuous strand is synthesised that grows towards the replication fork is called

• A. leading strand
• B. complementary strand
• C. leading template
• D. lagging template.

Answer 1

Answer: (C)

DNA polymerase, enzyme can cause polymerisation only in $5^{{}^{\prime }}\to 3^{{}^{\prime }}$ direction on $3^{{}^{\prime }}\to 5^{{}^{\prime }}$ strand because it adds them at the $3^{{}^{\prime }}$ end. Since the two strands of DNA run in antiparallel directions, the two templates provide different ends for replication. Consequently, replication is continuous on one strand while it is discontinuous on the other strand. The strand which opens from $3^{{}^{\prime }}\to 5^{{}^{\prime }}$ is called leading template and its complementary strand is called leading strand. It is constructed continuously at a faster rate. The other strand which opens from $5^{{}^{\prime }}\to 3^{{}^{\prime }}$ is called lagging template and its complementary strand is called lagging strand. It is constructed discontinuously at a slower rate. The lagging strand is constructed in the form of short fragments of DNA (Okazaki fragments), in $5^{{}^{\prime }}\to 3^{{}^{\prime }}$ direction, which are later joined by the enzyme DNA ligase. Each Okazaki fragment needs one RNA primer. Later, RNA primer is removed by the enzyme RNase.