Which of the following statements is true of restriction enzymes?
(a)they are not naturally produced by bacteria, but are bioengineered by humans.
(b)they cleave dna only at sites of adjacent thymine bases.
(c)there are less than 10 restriction enzymes known.
(d)they cut at random sites within a genome. they protect bacterial cells from invasion by foreign dna.

They protect bacterial cells from invasion by foreign DNA.

Explanation:

These enzymes are endonucleases, that is, inside (hence the endo-inside prefix) of DNA molecules, cutting them into well-defined locations.

These are enzymes normally produced by bacteria and have the property of defending them from foreign DNA invasion usually from invading viruses. These enzymes always “poke” the DNA molecule at certain points, leading to the production of fragments containing sticky tips, which can bind to other tips of DNA molecules that have been cut with the same enzyme.

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