What Is The Differences between Endonuclease and Exonuclease?

So, what is the main difference between endonuclease and exonuclease? The former cleaves nucleic acid strand at the middle whereas the latter cleaves nucleic acid strands from the ends.

Enzymes are substances produced by living organisms to act as a catalyst to bring about biochemical reactions. There are several types of enzymes in the body such as nuclease and amylase.  Nuclease is a type of enzyme whose function is to hydrolyze the nucleic acid of the DNA and RNA. This enzyme is further subdivided into endonuclease and exonuclease. 

Many students pursuing microbiology tend to find it challenging to tell their differences and even state examples during the exam. No need to worry as we got your back.  This article provides further differences between endonuclease and exonuclease in a tabular form. Take the time to read through it and also find out more about their similarities and examples.

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Differences between Endonuclease and Exonuclease(With Table)

Basic Terms Endonuclease Exonuclease
Meaning This is an enzyme that cleaves the polynucleotide chain and separates the nucleotides This is an enzyme that cleaves the polynucleotide chain at the end and removes nucleotides one after the other.
Mechanism Action Cleave nuclei acid at the middle. Cleave the nuclei acid at the end.
Lag Phase Undergo a lag period before their activity Does not undergo lag period before activity
Final Result Result in oligonucleotides Result in single nucleotides.
Blunt Ends Form either sticky or blunt ends Form sticky ends only
Function Block entry of pathogens causing diseases Have no significant role
Examples Restriction enzymes, DNases, and S1 nuclease Spleen phosphodiesterase, polymerase III of 3’ to 5’, and Snake venom

What is Endonuclease?

Endonucleases are enzymes that play a crucial role in nucleic acid metabolism, specifically in the cleavage of phosphodiester bonds within the interior of DNA or RNA strands. Unlike exonucleases, which remove nucleotides from the ends of the nucleic acid chain, endonucleases act at specific recognition sequences, cutting the molecule at precise locations along its length.

These enzymes are essential for various cellular processes, including DNA repair, recombination, and the defense mechanisms of bacteria through restriction digestion. In DNA repair, endonucleases precisely cleave damaged or mismatched sequences, allowing for subsequent repair processes to take place. In recombination, endonucleases are involved in the exchange of genetic material between homologous DNA strands.

In bacteria, restriction endonucleases are particularly noteworthy. These enzymes recognize specific DNA sequences, known as recognition or restriction sites, and cleave the DNA at or near these sites. Restriction endonucleases play a pivotal role in the defense mechanisms of bacteria against invading viral DNA by cutting it at specific recognition sites.

The action of endonucleases generates fragments of DNA or RNA with free ends, which can then undergo further processing or participate in cellular processes. The specificity of endonucleases for particular sequences contributes to their diverse roles in maintaining genomic integrity and regulating genetic information within cells.

What is Exonuclease?

Exonucleases are enzymes involved in nucleic acid metabolism, specifically in the removal of nucleotides from the ends of DNA or RNA strands. Unlike endonucleases, which cleave phosphodiester bonds within the interior of the nucleic acid chain, exonucleases act sequentially by cleaving nucleotides one at a time from either the 3′ or 5′ end of the molecule.

Exonucleases play critical roles in various cellular processes, including DNA repair, DNA replication, and mRNA degradation. During DNA replication, exonucleases function in proofreading, removing incorrectly incorporated nucleotides to maintain the accuracy of the newly synthesized DNA strand. In DNA repair, these enzymes participate in the excision of damaged or mismatched nucleotides.

In mRNA degradation, exonucleases are involved in the controlled removal of nucleotides from the 3′ end of the mRNA molecule. This process is essential for regulating gene expression and ensuring the timely degradation of mRNA transcripts when they are no longer needed.

The sequential removal of nucleotides by exonucleases allows for a gradual shortening of the nucleic acid chain. This activity is crucial for maintaining the integrity and fidelity of genetic information within the cell. Exonucleases contribute to the dynamic and regulated processes that govern nucleic acid metabolism, ensuring the accuracy and functionality of DNA and RNA molecules in various cellular contexts.

Differences Between Endonuclease and Exonuclease

  1. Endonuclease tends to separate the nucleotide chain into two or more fragments while exonuclease separate nucleotide chain one by one.
  2. Endonuclease cleaves the polynucleotide chain at the middle while exonuclease cleaves the polynucleotide chain at the end.
  3. The endonuclease is sequence-specific while on other hand exonuclease is non-sequence specific.
  4. Endonuclease undergoes lag phase before activity while exonuclease does not undergo lag phase before activity.
  5. Exonuclease results in the formation of a nucleotide that lacks a phosphate group while endonuclease results in oligonucleotides which is a short form of nucleotide.

Similarities of Endonuclease and Exonuclease

  1. Both are types of nuclease enzyme which cleave nucleic acid
  2. Both act on DNA and RNA
  3. Both are involved in the repair of DNA in a cell

Frequently Asked Questions

  • Is DNA Polymerase an Exonuclease?

Yes. They are responsible for detecting base-pair mismatches and further performs in the removal of the incorrect nucleotide to be replaced by the correct one.

  • Is a Restriction Enzyme an Endonuclease or an Exonuclease?

Restriction enzymes are endonucleases from eubacteria and archaea that recognize a specific DNA sequence.

  • Do Humans Have Restriction Enzymes?

Yes. HsaI is a restriction enzyme from a human being. The same restriction enzyme from the embryos of humans of Homo Sapiens. 

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Summary

Endonucleases and exonucleases are enzymes involved in nucleic acid metabolism, particularly DNA and RNA, but they differ in their specific roles, mechanisms, and locations of action within the nucleic acid molecules.

Endonucleases are enzymes that cleave the phosphodiester bonds within the interior of a DNA or RNA strand. They act at specific recognition sequences, often cutting the nucleic acid molecule at precise locations. Endonucleases are essential for processes like DNA repair, recombination, and restriction digestion in bacteria. They create breaks in the middle of the nucleic acid chain, resulting in fragments with free ends.

Exonucleases, on the other hand, are enzymes that cleave nucleotides from the ends of a DNA or RNA strand. They work by removing nucleotides one at a time from either the 3′ (exonuclease) or 5′ (exonuclease) end of the nucleic acid molecule. Exonucleases play crucial roles in DNA repair, proofreading during DNA replication, and mRNA degradation. The removal of nucleotides from the ends is a sequential process, gradually shortening the nucleic acid chain.

The primary distinction between endonucleases and exonucleases lies in their cutting sites and mechanisms. Endonucleases cleave within the nucleic acid chain at specific recognition sequences, generating fragments with free ends. Exonucleases, on the other hand, remove nucleotides from the ends of the nucleic acid chain, either from the 3′ or 5′ end, in a sequential manner. Both types of enzymes are essential for maintaining the integrity and functionality of nucleic acids in various cellular processes.

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