Lagging strand

Definition

The lagging strand is one of the two strands of DNA being replicated during DNA synthesis, characterized by its discontinuous replication in short segments called Okazaki fragments. This strand is synthesized in the opposite direction to the replication fork, necessitating multiple starting points for DNA polymerase to work effectively. As a result, the lagging strand plays a critical role in ensuring accurate and complete DNA replication in prokaryotes.

5 Must Know Facts For Your Next Test

1. The lagging strand is synthesized in short segments due to the antiparallel nature of DNA, where one strand is built continuously (leading strand) while the other must be built in pieces.
2. Each Okazaki fragment on the lagging strand is initiated by an RNA primer laid down by primase, which is then extended by DNA polymerase.
3. After synthesis, Okazaki fragments are connected together by the enzyme DNA ligase, creating a continuous DNA strand from the previously separate fragments.
4. In prokaryotes, the entire process of DNA replication occurs in the cytoplasm, as they lack a defined nucleus.
5. The efficiency and accuracy of lagging strand synthesis are vital for maintaining genomic integrity during cell division in prokaryotic organisms.

Review Questions

• How does the synthesis of the lagging strand differ from that of the leading strand during DNA replication?
  • The lagging strand is synthesized discontinuously in short segments known as Okazaki fragments, while the leading strand is synthesized continuously in the same direction as the replication fork. This difference arises because DNA polymerase can only add nucleotides in a 5' to 3' direction. Therefore, as the replication fork opens up, the leading strand can be built straight through, whereas the lagging strand must start anew at several points due to its opposite orientation relative to the fork.
• What role do Okazaki fragments play in the context of lagging strand synthesis, and how are they processed after their formation?
  • Okazaki fragments are crucial components of the lagging strand that allow for its discontinuous synthesis. Each fragment begins with an RNA primer laid down by primase, which is then extended by DNA polymerase. Once all fragments are synthesized, they are joined together by DNA ligase, resulting in a complete and continuous DNA molecule. This processing ensures that despite its segmented nature during initial synthesis, the final product is an intact and functional DNA strand.
• Evaluate how issues with lagging strand synthesis can impact prokaryotic cell division and overall genomic stability.
  • Problems with lagging strand synthesis can lead to incomplete or inaccurate replication of DNA, which may result in mutations or genomic instability. If Okazaki fragments are not properly joined or if primers are not correctly removed, it can create gaps or errors in the DNA sequence. These issues can hinder prokaryotic cell division by causing defects in daughter cells or potentially leading to cell death. Additionally, persistent replication errors can accumulate over generations, contributing to evolutionary changes or vulnerabilities within bacterial populations.

Related terms

Okazaki fragments:

Short segments of DNA synthesized on the lagging strand during replication, which are later joined together by DNA ligase.

DNA polymerase:

An enzyme responsible for synthesizing new DNA strands by adding nucleotides to a growing chain, crucial for both leading and lagging strand synthesis.

Replication fork: The Y-shaped region where the double-stranded DNA splits into two single strands during replication, allowing access for replication machinery.