Endonuclease vs Exonuclease- Definition, 11 Differences, Examples


Endonucleases are a type of enzymes that can cut the phosphodiester bonds within a polynucleotide chain, such as DNA or RNA. These bonds link the nucleotides together and form the backbone of the chain. By breaking these bonds, endonucleases can split a long chain into smaller fragments.

The name endonuclease comes from the fact that these enzymes can cut the chain from the inside, rather than from the ends. This means that they can recognize and cleave specific sequences within the chain, rather than removing nucleotides one by one from the termini.

Endonucleases are classified into two main groups: restriction endonucleases and non-restriction endonucleases. Restriction endonucleases are highly specific and can only cut certain sequences that are usually four to eight nucleotides long. These sequences are called restriction sites and are often palindromic, meaning that they read the same in both directions. For example, the sequence GAATTC is a restriction site for the enzyme EcoRI, which cuts between G and A.

Non-restriction endonucleases are less specific and can cut a variety of sequences, depending on their structure and function. Some of these enzymes are involved in DNA repair, recombination, transcription, or apoptosis. For example, the enzyme T4 endonuclease V can recognize and cut DNA that has been damaged by ultraviolet light.

Endonucleases can also be categorized based on their mechanism of action. Some endonucleases cut both strands of a double-stranded DNA molecule at the same position, creating blunt ends. Others cut the strands at different positions, creating sticky ends or overhangs that can be used for ligation. Some endonucleases can also cut single-stranded DNA or RNA molecules.

Endonucleases play an important role in molecular biology and biotechnology, as they enable the manipulation and analysis of DNA and RNA molecules. For example, restriction endonucleases are widely used for cloning, mapping, sequencing, and modifying DNA. Non-restriction endonucleases are also useful for studying DNA damage and repair, gene expression, and cell death.