A
Are used in genetic engineering for ligating two DNA molecules
B
Are used for in vitro DNA synthesis
C
Are synthesized by bacteria as part of their defense mechanism
D
Are present in mammalian cells for degradation of DNA when the cell dies
The answer is C.
Solution
Restriction endonucleases are enzymes that recognise specific palindromic base sequences in DNA and cut the DNA at or near those sites. They are produced by bacteria as a defence mechanism against bacteriophages. When phage DNA enters, the enzyme cuts it into pieces and so restricts the growth of the virus. The bacterium protects its own DNA by methylating its recognition sites with a methylase. Joining (ligating) DNA molecules is done by DNA ligase; in vitro DNA synthesis is done by DNA polymerase (e.g. in PCR). So restriction endonucleases are synthesised by bacteria as part of their defence mechanism.
ConceptNatural role of restriction enzymes
Restriction Enzymes in past papers
15 questions from this chapter have appeared across 12 exam years.
