Restriction Enzymes & Recombinant DNA — NEET Biology
✅ Asked in NEET 2015The cutting of DNA at specific locations became possible with the discovery of: (AIPMT 2015)
The cutting of DNA at specific locations became possible with the discovery of: (AIPMT 2015)
Answer & NCERT explanation
Correct answer: D — Restriction enzymes
Restriction enzymes or restriction endonucleases are molecular scissors that cut DNA at specific recognition sequences. Their discovery revolutionized genetic engineering by allowing precise cutting of DNA at predetermined sites. Probes detect sequences, ligases join DNA, and selectable markers help identify transformed cells, but only restriction enzymes can cut DNA at specific locations.
Read more NCERT concept on the PYQ
Let us now focus on the first instance of the construction of an artificial recombinant DNA molecule. The construction of the first recombinant DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native plasmid (autonomously replicating circular extra-chromosomal DNA) of Salmonella typhimurium. Stanley Cohen and Herbert Boyer accomplished this in 1972 by isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance. The cutting of DNA at specific locations became possible with the discovery of the so-called
NTA tests whether students understand that restriction enzymes (restriction endonucleases) are the key tools that enabled cutting DNA at specific locations, making recombinant DNA construction possible. Students often confuse restriction enzymes with other enzymes like ligase or polymerase, or forget their specificity to recognize palindromic sequences. The critical point: restriction enzymes cut DNA at specific recognition sites (usually 4-6 bp palindromic sequences), producing sticky or blunt ends. Remember: Cohen and Boyer used restriction enzymes to isolate the antibiotic resistance gene in 1972—this breakthrough revolutionized genetic engineering. This concept remains fundamental to biotechnology and appears frequently in NEET because understanding enzyme specificity is essential for all recombinant DNA techniques.
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