Read the following passage carefully.
Restriction enzyme
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. This leaves single stranded portions at the ends. There are overhanging stretches called sticky ends on each strand. These are named so because they form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase. The word palindromes refer to group of letters that forms the same words when read both forward and backward. Restriction endonucleases are used in genetic engineering as molecular scissors.
Which one of the following option is correct about restriction enzyme?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → This is known as molecular scissors.
A restriction enzyme recognises a specific palindromic sequence in DNA and cuts the DNA at that place. Because it cuts DNA so precisely, it is called the molecular scissors of genetic engineering.
Option (1) It helps in binding of DNA. — Incorrect. Joining DNA pieces is the work of DNA ligase, not of a restriction enzyme.
Option (2) This is known as molecular scissors. — Correct. Restriction endonucleases are used as molecular scissors, as the passage says.
Option (3) It has ability to multiply copies of plasmid. — Incorrect. A plasmid is copied inside the host cell from its origin of replication (ori). The enzyme only cuts.
Option (4) It helps in transfer of piece of DNA. — Incorrect. Carrying a piece of DNA into a host is the job of a vector, such as a plasmid.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.