Question

Which of the following statements are not true regarding restriction endonucleases?
A. They are called molecular scissors.
B. These are the enzymes responsible for restricting the growth of bacteriophages in {E. coli}.
C. They cut the DNA only at the centre of the palindromic sites.
D. They remove nucleotides only from the ends of DNA fragments.
E. They recognise specific palindromic base-pair sequences. Choose the answer from the options given below:

• A. A and E only
• B. D and E only
• C. A and B only
• D. C and D only

Hint:

\textbf{Exo} means \textbf{Exit/End} (removes from ends). \textbf{Endo} means \textbf{Inside} (cuts within the strand).

Answer 1

The Correct Option is D

Restriction endonucleases are a class of enzymes that function as part of the bacterial defense system.
• Statement C is Not True: Restriction enzymes do not usually cut exactly at the center of the palindromic sequence. Instead, they cut the two strands of DNA at specific points, often slightly away from the center of the palindrome, but between the same two bases on opposite strands, creating "sticky ends."
• Statement D is Not True: Removing nucleotides from the ends of DNA is the function of exonucleases. Endonucleases make cuts at specific positions within the DNA.
• Statements A, B, and E are True: They are indeed molecular scissors, part of the bacterial defense against phages, and they recognize specific palindromic sequences.