Lagging strand

Definition

The lagging strand is one of the two strands of DNA that is synthesized discontinuously during DNA replication, creating short segments known as Okazaki fragments. This occurs because DNA polymerase can only add nucleotides in the 5' to 3' direction, resulting in the lagging strand being synthesized away from the replication fork. The discontinuous nature of the lagging strand is critical for ensuring that the entire DNA molecule is accurately replicated.

5 Must Know Facts For Your Next Test

1. The lagging strand is synthesized in short bursts called Okazaki fragments, which are later connected by DNA ligase.
2. This strand runs in the opposite direction to the leading strand, meaning its synthesis occurs away from the replication fork.
3. Each Okazaki fragment begins with an RNA primer, which is necessary for DNA polymerase to start synthesizing DNA.
4. As replication progresses, the lagging strand must frequently re-initiate synthesis at new RNA primers due to its discontinuous nature.
5. The complexity of lagging strand synthesis adds an extra layer of regulation and coordination during DNA replication, ensuring complete and accurate duplication of genetic material.

Review Questions

• How does the structure and function of the lagging strand differ from that of the leading strand during DNA replication?
  • The lagging strand differs from the leading strand primarily in its method of synthesis. While the leading strand is synthesized continuously in the same direction as the replication fork, the lagging strand is synthesized discontinuously in short segments called Okazaki fragments. This discontinuity requires multiple initiation points and RNA primers, making it a more complex process compared to the leading strand's straightforward synthesis.
• Discuss the role of Okazaki fragments in the synthesis of the lagging strand and their significance in DNA replication.
  • Okazaki fragments are crucial for the synthesis of the lagging strand because they enable the overall process of DNA replication to occur despite the constraints imposed by directional synthesis. Each fragment begins with an RNA primer, allowing DNA polymerase to synthesize new DNA. After these fragments are produced, they are joined together by DNA ligase, ensuring that the entire lagging strand is properly assembled. This mechanism highlights how cells adapt their replication strategies to efficiently duplicate their genetic material.
• Evaluate how errors in lagging strand synthesis could impact genetic integrity and what mechanisms exist to correct these errors.
  • Errors during lagging strand synthesis can lead to mutations that affect genetic integrity, potentially causing issues like cancer or hereditary diseases. The presence of Okazaki fragments increases the risk for such errors due to multiple initiation sites. However, cells have evolved proofreading mechanisms, such as exonuclease activity of DNA polymerases, and repair pathways like mismatch repair that can identify and correct these mistakes. This intricate system emphasizes the importance of accuracy in DNA replication and its potential consequences for organismal health.

Related terms

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

leading strand: The other strand of DNA that is synthesized continuously in the same direction as the replication fork during DNA replication.

DNA polymerase: An enzyme that synthesizes new DNA strands by adding nucleotides to a growing chain during DNA replication.