Question

A restriction endonuclease enzyme binds to the DNA and cuts

• A. any one strand of the double helix
• B. each of the two strands at specific points in their base - sugar bonds
• C. each of the two strands at specific points in their base - phosphate bonds
• D. each of the two strands at specific points in their sugar- phosphate backbone

Answer 1

The correct option is D each of the two strands at specific points in their sugar- phosphate backbone

Restriction enzymes are the endonucleases that cleave the phosphodiester bonds present between the consecutive nucleotides within or near to specific DNA sequences known as recognition sequences. They make cuts in both the strands of the DNA. They are also called ‘molecular scissors’ or ‘biological scissors’ because they cut the DNA into multiple fragments.

For example, EcoR I is a restriction endonuclease enzyme. It recognises the base sequence 5’ GAATTC 3’ in the double stranded DNA and makes the cuts at both the strands between G and A.
The figure below shows that the restriction enzyme EcoR I cuts each of the two strands at a specific points in their sugar-phosphate backbone.