Key Difference – DNA Ligase vs DNA Polymerase
DNA ligase and DNA polymerase are important enzymes involved in DNA replication and DNA repair mechanisms of organisms. DNA ligase is responsible for joining DNA fragments by catalyzing the formation of phosphodiester bonds between nucleotides. DNA polymerase is responsible for synthesis of DNA from its building blocks (nucleotides) using template DNA. This is the key difference between DNA ligase and DNA polymerase.
CONTENTS
1. Overview and Key Difference
2. What is DNA Ligase
3. What is DNA Polymerase
4. Side by Side Comparison – DNA Ligase vs DNA Polymerase
5. Summary
What is DNA Ligase?
DNA ligase is an enzyme which catalyzes the formation of phosphodiester bond between 3’ – OH and 5’- PO4 groups of nucleotides and facilitates the joining of DNA fragments. It is also known as a molecular stitcher. This ability enables the filling the gaps or the nicks of DNA and joining Okazaki fragments formed during DNA replication. DNA ligases are highly useful in recombinant DNA technology for the production of the recombinant DNA molecules. DNA ligase joins DNA of interest with vector DNA. Therefore, it is an important enzyme for organisms.
DNA ligase enzyme depends on a cofactor and Mg2+ ions for its function. There are two cofactors that help in DNA ligases. NAD+ acts as a cofactor for bacterial DNA ligases while ATP often acts as a cofactor virus and eukaryotic DNA ligases. Eukaryotic DNA ligase action completes via three main steps.
Step 01. DNA ligase attacks ATP molecule and releases pyrophosphate (two phosphate group) and AMP, and forms ligase-adenylate intermediate by binding covalently with resultant AMP.
Step 02: Formed enzyme AMP intermediate transfers AMP to the 5’ phosphate of the nick and forms DNA – adenylate (5′-phosphate oxygen of the DNA strand attacks the phosphorus of ligase-adenylate intermediate).
Step 03: DNA ligase catalyzes attack of the 3′-OH of the nick on DNA-adenylate to join the polynucleotides and liberates AMP.
DNA ligases are usually isolated from T4 bacteriophage and extensively used in recombinant DNA technology.
Figure 01: DNA ligase in nick repair
What is DNA Polymerase?
DNA polymerase is a ubiquitous enzyme present in all organisms involved in DNA synthesis and genome replication. Genetic information passes from parent to offspring with the aid of DNA polymerases. It catalyzes the synthesis of new DNA complementary for the existing DNA. DNA polymerase adds nucleotides (building blocks of nucleic acids) to the 3’ OH group of the primer sequence and continues the strand formation to 5’ direction. Most of the DNA polymerases have 5’ to 3’ polymerase activity and 3’ to 5’ exonuclease activity for proofreading.
Prokaryotic DNA polymerases are described under five major groups. Eukaryotes contain at least 16 different DNA polymerases. All these DNA polymerases are grouped into seven families namely A, B, C, D, X, Y, and RT (Reverse transcriptase).
Figure 02: DNA polymerase driven DNA replication
What is the difference between DNA Ligase and DNA Polymerase?
DNA Ligase vs DNA Polymerase |
|
| DNA ligase is an enzyme which catalyzes the formation of phosphodiester bonds between nucleotides and connects DNA fragments together. | DNA polymerase is an enzyme which catalyzes the synthesis of DNA using nucleotides. |
| Role in DNA Replication | |
| DNA ligase is an additional enzyme in DNA replication which joins Okazaki fragments. | DNA polymerase is the main enzyme in DNA replication. |
| Requirements | |
| It depends on Mg2+ ions and ATP/NAD+ cofactors | It depends on a template, nucleotides, primers and Mg2+. |
| Functions | |
| DNA ligase is important for DNA recombination, DNA repair and DNA replication. | DNA polymerase is important for DNA replication, DNA repair and DNA recombination technology. |
Summary – DNA Ligase vs DNA Polymerase
DNA ligase is an important enzyme which is needed for joining DNA fragments by phosphodiester bonds. DNA polymerase is the main enzyme important for new DNA synthesis. The key difference between DNA ligase and DNA polymerase is their function. However, both enzymes are essential for DNA repairing, DNA replication and recombinant DNA technology.
Reference:
Rossi, R., A. Montecucco, G. Ciarrocchi, and G. Biamonti. “Functional characterization of the T4 DNA ligase: a new insight into the mechanism of action.” Nucleic Acids Research. U.S. National Library of Medicine, 01 June 1997. Web. 11 Mar. 2017
Martin, Ina V., and Stuart A. MacNeill. “ATP-dependent DNA ligases.” Genome Biology. BioMed Central, 2002. Web. 11 Mar. 2017
Garcia-Diaz, Miguel, and Katarzyna Bebenek. “Multiple functions of DNA polymerases.” Critical reviews in plant sciences. U.S. National Library of Medicine, Mar. 2007. Web. 11 Mar. 2017
Image Courtesy:
1. “Ligase nick repair mecanism” By Jrmcnall – ChemDraw (CC BY-SA 3.0) via Commons Wikimedia
2. “Phage T7 replication machinery” By Danykl – Own work (CC BY-SA 4.0) via Commons Wikimedia