Question

First discovered restriction endonuclease that always cuts DNA molecule at a particular point by recognising a specific sequence of six base pairs is:

• A. EcoR I
• B. Adenosine deaminase
• C. Thermostable DNA polymerase
• D. Hind II

Answer 1

The correct option is D Hind II

Restriction endonucleases are enzymes that cleave the phosphodiester bonds present between consecutive nucleotides within or near to specific DNA sequences that they identify.

The first restriction endonuclease characterized was Hind II. It was isolated from the bacterium, Haemophilus influenzae. It recognises a specific sequence of six base pairs.

EcoR I is also REN and is isolated from the bacterium Escherichia coli.

Adenosine deaminase (ADA) is an enzyme crucial for the functioning of the immune system. It converts deoxyadenosine (formed when DNA is broken down), which is toxic to lymphocytes, to deoxyinosine, which is not toxic.

The DNA polymerase enzyme catalyzes the synthesis of DNA. Thermostable DNA polymerase is purified from Thermus aquaticus, a bacterium which can survive at very high temperatures. In addition to adding deoxynucleotides, it does not get denatured at high temperatures during the denaturation step of PCR.