Question

Answer the following questions about DNA replication.

A. On a DNA strand that is being synthesized, which end is growing–the 3′ end, the 5′ end, or both ends? Explain your answer.
B. On a DNA strand that is being used as a template, where is the copying occurring relative to the replication origin–3′ of the origin, 5′, or both?

Answer 1

The growing end of a DNA strand being synthesized is the 3' end, and replication occurs in different directions depending on the strand. Polymerase adds nucleotides in the 5' to 3' direction, and the leading strand is synthesized towards the replication fork.

Step-by-step explanation:

The growing end of a DNA strand being synthesized is the 3' end. This is because DNA polymerase reads the template strand in the 3' to 5' direction and adds nucleotides only in the 5' to 3' direction. The leading strand is synthesized towards the replication fork, while replication on the lagging strand occurs in the direction away from the replication fork in short stretches called Okazaki fragments.

The 3' end is indeed the growing end of a DNA strand during synthesis. This directional specificity is a consequence of the enzymatic activity of DNA polymerase, which reads the template strand in the 3' to 5' direction and synthesizes the new strand in the 5' to 3' direction. This fundamental principle of DNA replication is crucial for maintaining the integrity of genetic information.

During DNA replication, the leading strand is synthesized continuously towards the replication fork, following the direction of the unwinding DNA. Conversely, the lagging strand is synthesized discontinuously in the opposite direction away from the replication fork. Replication on the lagging strand occurs in short, complementary fragments called Okazaki fragments. These fragments are later joined by DNA ligase to form a continuous, newly synthesized strand, ensuring accurate and complete replication of the entire DNA molecule.