Question

Which of the following correctly depicts the endonuclease activity of EcoR I?

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

Restriction enzymes are a type of endonucleases that cleave phosphodiester bonds between consecutive nucleotides within or near to specific DNA sequences. These are known as recognition sequences that are usually palindromic in nature. Palindromic sequences are DNA sequences that are read the same way forward or backward when the polarity is kept the same in both the strands.

EcoR I is a restriction endonuclease enzyme. It has been isolated from the bacteria Escherichia coli RY13. It recognises the base sequence 5’ GAATTC 3’ in the double stranded DNA and makes the cuts between G and A in both the strands. It results in the formation of single stranded overhangs known as sticky ends.
The recognition site on which it acts is shown below:
The figure below depicts that it makes the cuts between G and A and produces sticky ends.


In option a, the same sequence is found but the cut is being done between T and A.
In option b and c, their sequences do not match with the recognition sites for EcoR I.
Therefore, option d is the correct choice.