Lagging strand

Definition

The lagging strand is one of the two strands of DNA being synthesized during DNA replication, characterized by its discontinuous synthesis in short segments known as Okazaki fragments. This strand is formed in the opposite direction of the replication fork movement and requires multiple RNA primers to initiate each fragment. Understanding its formation is crucial for grasping the overall process of DNA replication and the structural properties of DNA.

5 Must Know Facts For Your Next Test

1. The lagging strand is synthesized in short, discontinuous segments due to the antiparallel nature of DNA strands, meaning it is built away from the replication fork.
2. Each Okazaki fragment requires a separate RNA primer for synthesis, created by primase, before being extended by DNA polymerase.
3. After synthesis, Okazaki fragments are linked together by the enzyme DNA ligase to form a continuous DNA strand.
4. In eukaryotes, multiple lagging strands can be synthesized simultaneously due to the presence of multiple origins of replication on larger chromosomes.
5. The coordination between the leading and lagging strands ensures that both strands are replicated accurately and efficiently during the S phase of the cell cycle.

Review Questions

• How does the structure and orientation of the lagging strand impact its synthesis compared to the leading strand?
  • The lagging strand is synthesized in a discontinuous manner because it runs in the opposite direction of the replication fork's movement. This antiparallel orientation necessitates that it be made in short segments called Okazaki fragments, each requiring its own RNA primer for initiation. In contrast, the leading strand is synthesized continuously toward the fork, allowing for more efficient and straightforward replication.
• Discuss the role of Okazaki fragments in the context of lagging strand synthesis and how they are processed post-replication.
  • Okazaki fragments are crucial for synthesizing the lagging strand since this strand cannot be built continuously. Each fragment begins with an RNA primer laid down by primase and is extended by DNA polymerase. After all fragments are formed, they are joined together by DNA ligase to create a continuous strand, ensuring that genetic information is accurately copied and maintained.
• Evaluate how errors during lagging strand synthesis might affect overall genomic integrity and what mechanisms exist to mitigate these errors.
  • Errors during lagging strand synthesis can lead to mutations, potentially disrupting gene function or leading to disease. The presence of proofreading activity in DNA polymerases allows for correction of mismatched bases during replication. Additionally, post-replication repair mechanisms like mismatch repair further safeguard genomic integrity by identifying and repairing erroneous incorporation after replication has occurred.

Related terms

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

DNA polymerase: The enzyme responsible for adding nucleotides to a growing DNA strand during replication, ensuring accurate and efficient synthesis.

leading strand:

The other strand of DNA being synthesized during replication, which is made continuously in the same direction as the replication fork.