A specific recognition sequence identified by endonuclease to make cuts at specific positions within the DNA is -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Palindromic nucleotide sequence
Option (1) Poly (A) sequence — Incorrect. The poly (A) tail is a string of adenylate residues added to the 3′ end of hnRNA during processing. It is not a cutting site.
Option (2) Palindromic nucleotide sequence — Correct. A restriction endonuclease looks along the DNA for its own palindrome, such as GAATTC for EcoRI, and cuts both strands at that site.
Option (3) Okazaki sequence — Incorrect. There is no such sequence. The book speaks of Okazaki fragments, the short pieces made on the lagging strand during replication and later joined by DNA ligase.
Option (4) Degenerate primer sequence — Incorrect. A primer is a short piece of DNA that starts copying in PCR or replication. It is not something a restriction enzyme recognises.
NCERT Extract:
Restriction Enzymes – “… Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA. … These are groups of letters that form the same words when read both forward and backward, e.g., “MALAYALAM”. As against a word-palindrome where the same word is read in both directions, the palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same.”