Difference Between Exonuclease and Endonuclease
DNA is the genetic blueprint of living organisms and the integrity of this molecule is crucial for maintaining life. Nucleases are enzymes that catalyze the breakdown of nucleic acids, such as DNA and RNA. There are two major types of nucleases: exonucleases and endonucleases. Both enzymes play a significant role in DNA repair and replication, but they differ in their mechanism of action and specificity.
Exonucleases:
Exonucleases are enzymes that remove nucleotides from either the 3′ or 5′ end of a nucleic acid molecule. These enzymes degrade DNA or RNA in a step-by-step manner by cleaving a single nucleotide at a time from the end of a strand. Exonucleases are involved in various cellular processes such as DNA replication, DNA repair, DNA recombination, and RNA processing. Exonucleases function by recognizing the terminus of a nucleic acid strand and cleaving phosphodiester bonds between the nucleotides.
Endonucleases:
Endonucleases are enzymes that cleave the internal phosphodiester bonds of nucleic acid strands. Unlike exonucleases, which work on the ends of the DNA strand, endonucleases break the strand in the middle. The broken strand is then repaired by the cellular machinery. Endonucleases are diverse enzymes encoded by different genes and classified according to their cleaving mechanism, target sequence, chemical nature, and mode of action. For instance, restriction endonucleases are enzymes that specifically recognize and cleave DNA at specific sites, while repair endonucleases target damaged DNA.
Differences:
The main difference between exonucleases and endonucleases is their mechanism of action. Exonucleases degrade DNA or RNA from the ends of the nucleic acid strands, while endonucleases break the strand in the middle. Another difference is their specificity: exonucleases are non-specific enzymes that can cleave any nucleic acid substrate, whereas endonucleases are highly specific enzymes that recognize and cleave particular sequences or damaged DNA.
In conclusion, exonucleases and endonucleases are two essential enzymes involved in DNA repair and replication. While the former digests nucleic acid from the ends of the strand, the latter breaks the internal bonds of DNA. Understanding the differences in their mechanism of action and specificity is vital for targeted use in genetic engineering and biotechnology.
Table difference between exonuclease and endonuclease
| Exonuclease | Endonuclease |
|---|---|
| Exonucleases cleave nucleotides from the end of a polynucleotide chain. | Endonucleases cleave nucleotides at specific points within a polynucleotide chain. |
| Exonucleases can be either 3’ to 5’ or 5′ to 3’. | Endonucleases can be either single-stranded or double-stranded. |
| Exonucleases are involved in DNA repair and proofreading. | Endonucleases are involved in DNA replication, recombination and repair. |
| Examples of exonucleases include exonuclease I, II, III and Exonuclease T. | Examples of endonucleases include EcoRI, HindIII and BamHI. |