Question

Do eukaryotic cells have restriction endonucleases? Justify your answer.

Answer 1

Hint: Restriction endonuclease or restriction enzymes are a protein which are produced by bacteria. They cleave the DNA at specific sites and are also known as ‘molecular scissors.’

Complete Answer:
- Restriction endonucleases are naturally occurring defence mechanisms of bacteria to digest any foreign DNA molecule. Restriction endonucleases recognize specific sequences. It is in the DNA mostly 4-6 bp.
- If cut into fragments by breaking the phosphodiester linkage. The linkage is between two successive nucleotides of DNA.
- Now if these restriction sites may be present in bacterial DNA itself, then from restriction digestion the DNA methylase enzymes carry out methylation of DNA to protect their own DNA in bacteria. Eukaryotic DNA is highly methylated so these enzymes are not found in eukaryotes.
- From various strains of bacteria all the restriction endonucleases have been isolated . Bacteria have this enzyme as a defence mechanism to restrict the growth of bacteriophages. Examples like, HindIII, EcoRII.

Hence eukaryotic cells do not have restriction endonucleases.

Note: The DNA is highly highly methylated by an enzyme named methyless . This phenomenon is called methylation. It protects the DNA from the activity of restriction of enzymes. So eukaryotic cells do not have restriction endonucleases.