Question

Which of the following statements about restriction enzymes is incorrect?
A) They work on DNA extracted from all types of organisms.
B) They are used to glue short segments of DNA.
C) They come in many varieties, each with its DNA target sequence.
D) They are highly specific for their DNA target sequences.

Answer 1

Hint: Restriction enzymes cleave DNA sequences at random or specific recognition sites known as restriction sites. These enzymes are found in many different strains of bacteria where their biological role is to participate in cell defence. They restrict foreign DNA from entering the cell by destroying it.

Complete step-by-step answer:
Restriction enzymes are of two types restriction endonucleases and exonucleases. Exonucleases catalyze the terminal nucleotides and act on both RNA and DNA.
Endonucleases recognize specific base sequences within the nucleic acid molecule. Restriction endonuclease, first of all, inspects the length of the DNA sequence and performs its functions. So the first statement is true i.e., it works on DNA extracted from all types of organisms.
 Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at the specific points in their sugar-phosphate backbones. Restriction endonucleases recognize palindromic sequences in DNA. So the last statement is also correct i.e., they are highly specific for DNA target sequences.
Restriction endonucleases are used in genetic engineering to form recombinant molecules of DNA, which are composed of DNA from different sources so the statement third is also correct.
As we know that restriction enzymes help in cutting and nicking DNA
so this statement is incorrect that they are used to glue DNA fragments.

Therefore the correct answer is Option B.



Note: Restriction enzymes cut the strand of DNA a little away from the centre of the palindromic sites, but between the same two bases on the opposite strands. This leaves single-stranded ends these are overhanging stretches called sticky ends on each strand.