Restriction Endonuclease Discovery — NEET Biology
✅ Asked in NEET 2026Which of the following statements are not true regarding restriction endonucleases? A. They are called molecular scissors. B. They restrict bacteriophage growth in E. coli. C. They cut DNA only at the centre of palindromic sites. D. They remove nucleotides only from ends of DNA fragments. E. They recognise specific palindromic base-pair sequences.
Which of the following statements are not true regarding restriction endonucleases? A. They are called molecular scissors. B. They restrict bacteriophage growth in E. coli. C. They cut DNA only at the centre of palindromic sites. D. They remove nucleotides only from ends of DNA fragments. E. They recognise specific palindromic base-pair sequences.
Answer & NCERT explanation
Correct answer: D — C and D only
Restriction endonucleases cut DNA slightly off-centre within the palindrome (not exactly at the centre), and they are endonucleases that cut internally — they do not remove nucleotides from the ends. So C and D are wrong.
Read more NCERT concept on the PYQ
In the year 1963, the two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli were isolated. One of these added methyl groups to DNA, while the other cut DNA. The later was called restriction endonuclease.
Restriction endonucleases are enzymes that cut DNA at specific recognition sites, discovered in 1963 while studying how E. coli protects itself from bacteriophages. NTA tests whether students understand that these enzymes are the 'scissors' of genetic engineering—paired with methylase enzymes that protect host DNA. Students often confuse restriction endonucleases with methylases (which add methyl groups) or forget that they cut DNA at specific sequences, not randomly. Remember: restriction endonucleases recognize and cut DNA at palindromic sequences, producing sticky or blunt ends. This discovery was revolutionary because it made recombinant DNA technology possible—the foundation of genetic engineering tested frequently in NEET.
What does NCERT say about year 1963 two enzymes?
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Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.