Question

Which one of the following is NOT true regarding restriction endonucleases?

They are ______.

Options

• used for cloning DNA in PCR

• synthesized by bacteria as defense mechanism to destroy viral DNA

• used in genetic engineering for ligation of DNA fragments

• used to recognize short nucleotide sequence and cleave the DNA within them

Answer 1

They are used in genetic engineering for ligation of DNA fragments.

Explanation:

Restriction endonucleases (restriction enzymes) recognize short specific DNA sequences and cleave them; they are bacterial defence enzymes and are used to cut DNA for cloning. The joining (ligation) of DNA fragments is performed by DNA ligase, and PCR uses a thermostable DNA polymerase rather than restriction enzymes.