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Functioning of Restriction Endonucleases - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET

Quick Facts

  • Functioning of Restriction Endonucleases is considered one of the most asked concept.

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Functioning of Restriction Endonucleases


  • Each restriction endonuclease recognizes a specific palindromic nucleotide sequence in the DNA.
  • Palindromes are groups of letters that form the same words when reading both forward and backward, e.g., “MALAYALAM”. 
  • The palindrome in DNA is a sequence of base pairs that reads the same on the two strands when the orientation of reading is kept the same.
  • Restriction enzymes cut the strand of DNA a little away from the center of the palindrome sites, but between the same two bases on the opposite strands. 
  • The enzyme makes two incisions, one through each of the sugar-phosphate backbones (i.e., each strand) of the double helix without damaging the nitrogenous bases.
  • Patterns of DNA Cutting by Restriction Enzymes:
    • 5′ overhangs: The enzyme cuts asymmetrically within the recognition site such that a short single-stranded segment extends from the 5′ ends. BamHI cuts in this manner.
    • 3′ overhangs:  There is an asymmetrical cutting within the recognition site, but the result is a single-stranded overhang from the two 3′ ends. Kpnl cuts in this manner.
    • Blunt ends: Enzymes that cut at precisely opposite sites in the two strands of DNA generate blunt ends without overhangs. Smal is an example of an enzyme that generates blunt ends.
  • The 5′ or 3′ overhangs generated by enzymes that cut asymmetrically are called sticky ends or cohesive ends because they will readily stick or anneal with their partner by base pairing.

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