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Question: Restriction endonucleases A)Are present in mammalian cells for degradation of DNA when the cell di...

Restriction endonucleases
A)Are present in mammalian cells for degradation of DNA when the cell die.
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.

Explanation

Solution

An enzyme that cleaves DNA into fragments at or close unique recognition sites within molecules known as restriction sites is a restriction enzyme, constraint endonuclease, or restrictase. Restriction enzymes are one class of the broader endonuclease group of enzymes.

Complete answer:
Proteins formed by bacteria that cleave the DNA at unique locations along the molecule are restriction endonuclease or restriction enzymes or molecular scissors. In a bacterial enzyme, the restriction enzyme cleaves foreign DNA and thus kills infecting entities. Such enzymes may be separated from bacterial cells and used to affect DNA fragments, including those that contain chromosomes, in laboratories. This is why they are the main instruments of DNA recombinant technology.

Restriction enzymes with sticky ends are used for cloning.
(a) Simplicity of transition.
(b) Simple insertion of DNA segments from various sources into plasmids.
(c) Simple detection of antibiotic-resistance plasmids.
(d) Simple detection of plasmids containing inserts.
In bacteria and archaea, these enzymes are contained and provide a protective mechanism against invading viruses. Within a prokaryote, in a mechanism called restriction digestion, the restriction enzymes selectively break up foreign DNA; meanwhile, host DNA is shielded by a modification enzyme that modifies the prokaryotic DNA and blocks cleavage. Together, these two procedures form the method of restriction alteration.

Hence, the correct answer is option (D)

Note: Enzyme restriction, also referred to as endonuclease restriction, is a protein formed by bacteria that cleaves DNA at particular locations along the molecule. Restriction enzymes in the bacterial cell cleave foreign DNA, thereby preventing infecting cells.