Question

Mention the difference in the mode of action of exonuclease and endonuclease.

Answer 1

Hint: Exonuclease- It is an enzyme which removes the nucleotides from the end of the polynucleotide molecule.
Endonuclease- It is an enzyme that cleaves the phosphodiester bond within the polynucleotide chain.
The mode of action of endonuclease is to separate the nucleotide chain into two or more fragments whereas exonuclease separates the nucleotides at a time from a polynucleotide chain.

Complete answer:

Exonuclease	Endonuclease
Requires a free 3’ Or 5’ end for their reactions.	Do not require free 3’ and 5’ ends for their reactions.
Exonuclease cleaves the phosphodiester bond from ends.	Endonuclease cleaves the phosphodiester bond present internally in the polynucleotide chains.
Exonucleases are usually nonspecific.	Endonuclease is usually sequence specific.
Exonuclease after its hydrolytic reaction releases individual nucleotides.	Endonuclease after its hydrolytic reaction releases oligonucleotide chains.
The removal of bonds is from the end of the chain.	The removal of bond is from in-between the chain.
Example: Exonuclease 1, Exonuclease 2.	Example: Deoxyribonuclease 1, S1 Nuclease.

Note: Nucleases are a class of enzymes which hydrolysis the nucleic acids such as DNA and RNA. They hydrolyse the phosphodiester backbone which connects individual nucleotides in a polynucleotide chain. Both endonuclease and exonuclease are nuclease enzymes that can act on nucleic acids and can hydrolyse DNA and RNA. Polynucleotide chain is a sequence of nucleotides joined together generally containing one polynucleotide chain while DNA may consist of one chain (single stranded DNA) or two chains (double stranded DNA). The two chains of DNA show opposite polarities.