DNA ligase

Definition

DNA ligase is an enzyme that plays a crucial role in the process of DNA replication and repair by joining together the ends of DNA strands, forming phosphodiester bonds. This enzyme is essential for sealing nicks and gaps in the sugar-phosphate backbone of DNA, ensuring the integrity and continuity of the genetic material during replication and repair processes.

5 Must Know Facts For Your Next Test

1. DNA ligase is critical for joining Okazaki fragments on the lagging strand during DNA replication, ensuring continuous DNA synthesis.
2. In addition to replication, DNA ligase also participates in various DNA repair mechanisms by sealing breaks in the DNA backbone.
3. Different types of DNA ligases exist, with variations in their mechanisms and specificities; for example, prokaryotic and eukaryotic DNA ligases have distinct properties.
4. The action of DNA ligase requires ATP or NAD+ as a cofactor, which provides the energy necessary to form the phosphodiester bonds between nucleotides.
5. Mutations or deficiencies in DNA ligase can lead to severe consequences, including genomic instability and increased susceptibility to cancer.

Review Questions

• How does DNA ligase contribute to the overall fidelity of DNA replication?
  • DNA ligase enhances the fidelity of DNA replication by sealing nicks and gaps in the newly synthesized strands, particularly on the lagging strand where Okazaki fragments are formed. By joining these fragments into a continuous strand, DNA ligase helps prevent errors and maintains the integrity of the genetic information. Its activity ensures that all segments of the new DNA molecule are properly linked, thus minimizing potential mutations that could arise from incomplete or improper joining of DNA segments.
• Discuss the role of DNA ligase in both DNA replication and repair mechanisms, highlighting its importance in maintaining genomic stability.
  • DNA ligase plays a dual role in both DNA replication and repair processes. During replication, it connects Okazaki fragments on the lagging strand, facilitating complete and accurate synthesis of the new DNA strand. In repair mechanisms, such as nucleotide excision repair, it seals gaps left after damaged nucleotides are removed and replaced. This ability to join broken ends is vital for maintaining genomic stability; without effective action from DNA ligase, incomplete repairs could lead to mutations or chromosomal abnormalities.
• Evaluate the impact of defective DNA ligase on cellular functions and its potential link to cancer development.
  • Defective DNA ligase can severely impact cellular functions by compromising the integrity of DNA replication and repair pathways. When this enzyme is malfunctioning, it leads to an accumulation of unrepaired breaks and nicks in the DNA, which can result in genomic instability—a hallmark of cancerous cells. The failure to properly seal these breaks may allow for mutations to persist, leading to uncontrolled cell division and tumorigenesis. Consequently, understanding the function of DNA ligase is crucial not only for grasping basic molecular biology but also for developing potential therapeutic strategies against cancer.

Related terms

DNA polymerase: An enzyme responsible for synthesizing new DNA strands by adding nucleotides to a growing chain during DNA replication.

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

Nucleotide excision repair: A DNA repair mechanism that removes damaged or incorrect nucleotides from DNA and replaces them with the correct ones, often involving the action of DNA ligase to seal the newly synthesized segments.