Question

Which of the following statement does not hold true for restriction enzymes?

• A. It is endonuclease
  
• B. It recognizes palindromic nucleotide sequences
  
• C. It is isolated from bacteriophages and bacteria
  
• D. Different restriction enzymes produce different kinds of sticky or blunt ends depending upon their recognition sequence
  

Answer 1

The correct option is C It is isolated from bacteriophages and bacteria


Restriction endonuclease recognizes specific nucleotide sequences in a DNA molecule, often a palindrome known as restriction site, which cleaves the DNA at a specific nucleotide at the restriction site. Restriction endonucleases are naturally present in the bacteria where they provide protection against invading bacteriophage DNA. Bacterial DNA is protected from restriction endonuclease, even though it contains recognition sites by the action of an enzyme which methylates the nucleotides at the recognition site.

Upon action, restriction enzymes produce fragments with two types of ends namely blunt end and sticky end.
Blunt ends

• No overhangs are produced
• The cleavage site lies exactly on the axis of symmetry

Sticky ends

• Overhangs are produced either at 5’ or 3’ end
• The cleavage site is away from the axis of symmetry