Question

Restriction endonucleases

• A. are present in mammalian cells for degradation of DNA when the cell dies
• B. are used in genetic engineering for ligating two DNA molecules
• C. are used for in vitro DNA synthesis
• D. are synthesized by bacteria as part of their defense mechanism.

Answer 1

The Correct Option is D

To answer this question correctly, it's important to understand the role of restriction endonucleases and the context in which they operate.

Restriction endonucleases, also known as restriction enzymes, are enzymes that are synthesized by bacteria. They serve as a part of the bacterial defense mechanism against invading viral DNA.

Here is the reasoning for the correct answer:

1. Understanding Restriction Endonucleases:
   • These are enzymes that can cut DNA at specific sequences, known as restriction sites.
   • Primarily discovered in bacteria, restriction endonucleases protect the cell by lysing foreign DNA, such as that from bacteriophages (viruses that infect bacteria).
2. Correct Option Analysis:
   • The correct option states that they "are synthesized by bacteria as part of their defense mechanism."
   • This is true, as these enzymes help to identify and degrade the foreign DNA that enters the bacterial cell, protecting the bacteria from viral attacks.
3. Eliminating Other Options:
   • "Are present in mammalian cells for degradation of DNA when the cell dies" - Incorrect because restriction endonucleases are not characteristically found in mammalian cells for this purpose.
   • "Are used in genetic engineering for ligating two DNA molecules" - Incorrect as ligation refers to joining DNA fragments, which is done by DNA ligases, not restriction enzymes.
   • "Are used for in vitro DNA synthesis" - Incorrect since DNA polymerases are responsible for synthesizing DNA, not restriction enzymes.

Therefore, the correct answer is the option stating that restriction endonucleases "are synthesized by bacteria as part of their defense mechanism."