5 Differences between Endonuclease and Exonuclease(With Table)

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. 

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.

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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Comparison Table (Endonuclease Vs Exonuclease)

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?

Endonuclease enzyme is an enzyme that cleaves the bond of the DNA from within the molecule.

The good news is that the enzyme does not need a free 3’ or 5’ hydroxyl group mostly at the end of the polynucleotide chain.

However, the type of nuclease enzyme is known to attack the 3’ or 5’ hydroxyl linkages in the polynucleotide chain regardless of the location.

The enzyme is further subdivided into Deoxyribonuclease I and Deoxyribonuclease II. Deoxyribonuclease I is responsible for catalyzing 3’ linkages of DNA to result in oligonucleotides that tend to contain about four nucleotide residues.

On the other hand, Deoxyribonuclease II is responsible for causing the hydrolysis of 5’ linkages to yield a group of nucleotides.
Deoxyribonuclease I is isolated from a bovine pancreas while Deoxyribonuclease II from the spleen and thymus of certain types of bacteria.

What is Exonuclease?

Exonuclease enzyme is another type of nuclease enzyme that is known for cleaving the nucleotides at the end of DNA molecules.

The two strands of the DNA molecule are represented as 3’ and 5’ arms since they are complementary to each other.

The phosphodiester bridges of RNA and DNA are later attacked by two categories of the enzyme represented as “a” and “b”.

Enzyme “a” is responsible for hydrolyzing the ester linkage between 3’ carbon, and the phosphoric group. Enzyme “b” is responsible for hydrolyzing the ester linkage between 5’ carbon and phosphoric groups.

The venom of a rattlesnake and Russell’s viper are known to be a good example of the exonuclease of group “a”.

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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The main function of endonuclease and exonuclease is to separate mismatch nucleotides. Besides that, they play a significant role in DNA repair and stabilization.

The differences between endonuclease and exonuclease help to bring out the different functions they play. You should also note that they belong to the nuclease enzyme.

More Sources and References 

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