Leading strand

Definition

The leading strand is the continuous strand of DNA that is synthesized in the same direction as the replication fork during DNA replication. It is formed as a result of the addition of nucleotides to the growing strand, allowing for efficient and uninterrupted synthesis of DNA as it unwinds.

5 Must Know Facts For Your Next Test

1. The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short, discontinuous segments called Okazaki fragments.
2. DNA polymerase adds nucleotides to the 3' end of the leading strand, extending it as the replication fork opens up.
3. In prokaryotes, replication begins at a single origin and occurs bidirectionally, with leading strands forming on both sides of the fork.
4. The leading strand's synthesis is faster than that of the lagging strand due to its continuous nature, making it crucial for rapid cell division.
5. Despite being synthesized continuously, the leading strand still requires primase to lay down a short RNA primer before DNA polymerase can start adding nucleotides.

Review Questions

• How does the leading strand differ from the lagging strand in terms of its synthesis during DNA replication?
  • The leading strand is synthesized continuously in the same direction as the replication fork, allowing for a smooth and efficient addition of nucleotides. In contrast, the lagging strand is synthesized in short segments known as Okazaki fragments, which occur in the opposite direction of the replication fork. This difference in synthesis results from how DNA polymerase can only add nucleotides to the 3' end of a growing strand.
• Discuss the role of DNA polymerase and primase in the synthesis of the leading strand.
  • DNA polymerase is crucial for synthesizing the leading strand by adding nucleotides to its growing end. It works continuously as the replication fork progresses. However, before DNA polymerase can begin this synthesis, primase lays down an RNA primer that provides a starting point. This collaboration ensures that the leading strand can be synthesized efficiently and without interruption.
• Evaluate the importance of leading strand synthesis in prokaryotic cell division and how it relates to overall DNA replication efficiency.
  • Leading strand synthesis plays a vital role in prokaryotic cell division by allowing for rapid and efficient DNA replication. As prokaryotes often divide quickly, having a continuous leading strand means that they can replicate their genome with minimal delays. This efficiency not only supports faster cell division but also helps maintain genetic integrity during replication. By ensuring that one strand can be synthesized without interruption, prokaryotes are better equipped to adapt and thrive in various environments.

Related terms

DNA Polymerase: An enzyme that synthesizes new DNA strands by adding nucleotides to a pre-existing chain during DNA replication.

Lagging Strand: The strand of DNA that is synthesized in short segments, known as Okazaki fragments, in the opposite direction of the replication fork.

Replication Fork: The Y-shaped region where the double-stranded DNA is separated into two single strands, allowing for replication to occur.