DNA ligase

Definition

DNA ligase is an enzyme that facilitates the joining of DNA strands together by forming phosphodiester bonds. This enzyme is crucial in DNA replication, where it connects Okazaki fragments on the lagging strand and seals nicks in the sugar-phosphate backbone, ensuring the integrity of the newly synthesized DNA. By playing a key role in both prokaryotic and eukaryotic DNA replication processes, DNA ligase maintains genetic continuity and stability.

5 Must Know Facts For Your Next Test

1. DNA ligase is essential for sealing gaps between Okazaki fragments on the lagging strand during replication, which allows for a continuous DNA molecule.
2. In prokaryotes, DNA ligase is involved in both DNA replication and repair processes, helping to fix nicks caused by damage or incomplete replication.
3. Eukaryotic cells have multiple types of DNA ligases, with Ligase I being primarily responsible for lagging strand synthesis and Ligase III involved in repairing damaged DNA.
4. The action of DNA ligase requires ATP (adenosine triphosphate) or NAD+ (nicotinamide adenine dinucleotide) as a cofactor to provide the necessary energy for forming bonds.
5. In biotechnology, DNA ligase is widely used in molecular cloning and genetic engineering to join fragments of DNA, enabling researchers to create recombinant DNA molecules.

Review Questions

• How does DNA ligase function in the context of Okazaki fragment processing during DNA replication?
  • DNA ligase plays a critical role in processing Okazaki fragments by joining them together after they have been synthesized on the lagging strand. Once RNA primers are replaced with DNA nucleotides by DNA polymerase, there are still gaps between these fragments. DNA ligase seals these gaps by forming phosphodiester bonds, creating a continuous strand of DNA that is essential for the overall integrity of the replicated genome.
• Discuss the differences in the function and types of DNA ligases found in prokaryotic versus eukaryotic cells.
  • Prokaryotic cells typically have a single type of DNA ligase that performs both replication and repair functions. In contrast, eukaryotic cells contain multiple types of ligases, each with specific roles; for example, Ligase I is mainly involved in joining Okazaki fragments during lagging strand synthesis, while Ligase III is primarily associated with repairing damaged DNA. This specialization allows eukaryotic cells to manage their complex genomic structures more effectively.
• Evaluate the significance of DNA ligase in molecular biology applications, particularly in genetic engineering.
  • DNA ligase is pivotal in molecular biology applications like genetic engineering and cloning because it enables researchers to join specific DNA fragments together to form recombinant molecules. The ability to create hybrid genes or insert genes into vectors relies heavily on the action of DNA ligase to seal the nicks after fragment assembly. This capability allows for targeted modifications in genomes and contributes significantly to advancements in biotechnology, therapeutic development, and research into gene function.

Related terms

Okazaki fragments:

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

DNA polymerase:

An enzyme responsible for synthesizing new DNA strands by adding nucleotides complementary to the template strand during DNA replication.

Nuclease: An enzyme that cleaves the bonds between nucleotides in nucleic acids, often used to remove damaged or unnecessary segments of DNA before ligation.