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Difference between Exonuclease and Endonuclease

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Restriction enzymes: A discovery

The restriction enzyme originated from the research of phage λ, a virus that infects bacteria, and the phenomenon of host-managed restriction and modification of bacteriophage. The restriction enzymes studied through Arber and Meselson were type I restriction enzymes, which cleave DNA randomly far away from the recognition area or sites. In 1970, Hamilton O. Smith, Thomas Kelly, and Kent Wilcox insulated and characterized the primary kind II restriction enzyme, HindII, from the bacterium Haemophilus influenzae. Restriction enzymes of this kind are more beneficial for laboratory work as they cleave DNA on the area in their recognition series and are the most usually used as a molecular biology tool.

What are Restriction Enzymes?

Restriction enzymes also known as molecular scissors, are essential tools of in biotechnology. Their discovery has enabled the recognition and replacement of specific segment of DNA sequence in order to produce recombinant DNA. They are pretty cool, and there are at least 3,000 of them. Each of these enzymes cuts a selected or a specific DNA sequence and does not discriminate in which the DNA comes from — microorganism, fungi, mouse, or human. Based on the position at which these enzymes cut the sequence they recognize, they are classified as endonucleases and exonucleases.

What is Exonuclease?

Exonucleases are enzymes that work through cleaving nucleotides separately from the end of a polynucleotide chain. Exonuclease function involves a hydrolyzing response that breaks phosphodiester bonds at both the 3′ and the 5′ end occurs. Its near relative is the endonuclease, which cleaves phosphodiester bonds within the middle (endo) of a polynucleotide chain. Eukaryotes and prokaryotes have 3 kinds of exonucleases involved within the normal turnover of mRNA: 5′ to 3′ exonuclease (Xrn1), that is a dependent decapping protein; 3′ to 5′ exonuclease, an independent protein; and poly (A)-specific 3′ to 5′ exonuclease.

Examples of Restriction Exonuclease

Snake venom, Exonuclease I, and Xrn1 are the examples of exonuclease enzymes.

What is Endonuclease?

Endonucleases are enzymes that cleave the phosphodiester bond inside a polynucleotide chain. Some, including deoxyribonuclease I, cut DNA pretty nonspecifically, at the same time as many; commonly known as restriction endonucleases, cleave only at very specific nucleotide sequences. Endonucleases vary from exonucleases, which cleave the ends of recognition sequences rather than the middle (endo) portion. Some enzymes called "exo-endonucleases", however, aren't limited to both nuclease functions, showing characteristics which are both endo- and exo-like. Evidence shows that endonuclease activity experiences a lag as compared to exonuclease activity.

Example of restriction endonuclease

BamHI, EcoRV, EcoRI, HindIII, and HaeIII are examples of endonuclease enzymes.

Recombinant DNA Technology

Recombinant DNA technology contains changing genetic material outside an organism to attain improved and preferred traits in dwelling organisms or as their products. This technology includes the insertion of DNA fragments from a lot of sources, having a suitable gene series through a suitable vector. Manipulation in an organism's genome is accomplished both through the introduction of 1 or numerous new genes and regulatory factors or through lowering or blocking the expression of endogenous genes via recombining genes and factors.

Enzymatic cleavage is carried out to attain specific DNA fragments through the usage of restriction endo-nucleases for specific target series DNA sites accompanied by DNA ligase activity to enroll in the fragments to restore the preferred gene in the vector. The vector is then brought into a host organism that is grown to provide more than one copy of the integrated DNA fragment in culture, and finally, clones containing a relevant DNA fragment are selected and harvested.

Endonuclease vs Exonuclease

Restriction Endonuclease

Restriction Exonuclease

They are the enzymes that recognize DNA sequences, scan the series and cleave or cut the fragment around or within that sequence.

Exonuclease function by cleaving the polynucleotide sequence either from the 5’ end or the 3’ end, one at a time.

Found only in prokaryotes.

Found in both eukaryotes and prokaryotes.

After the cleavage, the product will be oligonucleotide chains.

In exonuclease, the product obtained after the activity is monomers of nucleotides.

Cuts DNA at specific recognition sites.

It cuts DNA at random sites.

A restriction endonuclease activity forms both the blunt ends and sticky ends.

It always forms sticky ends.

The Types of endonuclease are I, II, III, IV and V.

Types of exonuclease are 5’ to 3’ exonuclease, 3’ to 5’ exonuclease and poly (A) specific 3’ to 5’ exonuclease.

Endonuclease shows a lag period during their activity.

Exonuclease does not show any lag period.

This enzyme plays a role in blocking cells from pathogens.

It does not have any role in blocking pathogens.

Examples: EcoRI, BamHI, Hind III

Examples: Snake venom, exonuclease 1, XRN 1.

Interesting Facts

  • Restriction enzymes are helpful to bacteria.

  • They are non-discriminating and specific cutters.

  • Restriction enzymes have methyltransferases which methylate DNA.

  • The main in endonucleases vs exonucleases

Important Questions

1. What are the similarities between exonuclease and endonuclease?

Ans: Exonuclease and endonuclease both help in DNA repair within the cell. They act on both RNA and DNA.

2. Define restriction enzymes.

Restriction enzyme is a protein isolated from microorganisms that cleave DNA sequences at sequence-specific areas, generating DNA fragments with a recognised series at every end.

Key features of endonuclease and exonuclease

  • Restriction enzyme is a protein insulated from microorganisms that cleave DNA sequences at sequence-specific areas, generating DNA fragments with a recognised series at every end.

  • The use of restriction enzymes is essential to laboratory methods, along with recombinant DNA generation and genetic engineering.

  • Exonuclease enzymes work by cleaving nucleotides separately from the end of a polynucleotide chain.

  • Endonucleases are enzymes that cleave the phosphodiester bond inside a polynucleotide chain.

  • These enzymes are involved in recognising and cleaving up foreign DNA getting into the cell; their more possible function is shielding the microorganism from phage infection. The asset which is applicable to us is that those enzymes recognize specific DNA sequences.

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FAQs on Difference between Exonuclease and Endonuclease

1. Which type of restriction enzyme is most useful in genetic engineering and why?

There are 2 types of restriction enzymes, exonucleases and endonucleases. Endonucleases again have their types; one makes a blunt end that cuts within the gene, and the other makes sticky ends. So for the reason of getting rid of a segment of DNA from one organism and ligating it into another, the endonucleases, which make sticky ends come in handy. It is due to the fact you can't ligate segments of DNA except if they've sticky ends.

2. What does the Roman number after the name of any restriction enzyme indicate?

Roman number does not indicate the order of discovery. It shows the order of isolation of the limited enzyme from the specific strain of a microorganism. Since Hind-II was observed earlier than Hind-I, that is why the first discovered restriction enzyme is Hind-II. But Hind-I becomes first isolated from that strain of microorganism from which Hind-II becomes isolated later. That's why there is II within the first found endonuclease enzyme.

3. Why are endonucleases called restriction enzymes?

Restriction enzymes had been named for their cap potential to restrict the variety of strains of bacteriophage that may infect a bacterium.