Question Video: Using Restriction Enzymes | Nagwa Question Video: Using Restriction Enzymes | Nagwa

Question Video: Using Restriction Enzymes Biology • Third Year of Secondary School

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Which of the following statements about restriction enzymes is true? [A] All restriction enzymes cut DNA, leaving sticky ends, which allows the joining of different fragments of DNA. [B] Restriction enzymes cut at specific nucleotide sequences that are also palindromes. [C] Restriction enzymes were discovered in antibiotic-resistant strains of viruses. [D] A fragment of DNA produced by the action of one restriction enzyme is always joined with a fragment of DNA produced by the action of a different restriction enzyme.

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Video Transcript

Which of the following statements about restriction enzymes is true? (A) All restriction enzymes cut DNA, leaving sticky ends, which allows the joining of different fragments of DNA. (B) Restriction enzymes cut at specific nucleotide sequences that are also palindromes. (C) Restriction enzymes were discovered in antibiotic-resistant strains of viruses. (D) A fragment of DNA produced by the action of one restriction enzyme is always joined with a fragment of DNA produced by the action of a different restriction enzyme.

Restriction enzymes are important in combining different sources of DNA to make recombinant DNA. They are useful because they act like molecular scissors to cut DNA. These enzymes were discovered in bacteria as a defense against viral infection. So, answer choice (C) is incorrect.

Restriction enzymes cut DNA at specific nucleotide sequences called recognition sequences. This particular sequence is recognized by the restriction enzyme Eco R one. Eco R one cuts DNA like this. This produces two fragments that each have an overhang of unpaired nucleotides. These are called sticky ends because they can pair together with their complementary nucleotides from a compatible sticky end.

By using the same restriction enzyme, DNA from any source can be combined. This is how genetic engineering can be used to insert genes into organisms. If different restriction enzymes are used, then different sticky ends will be produced that are not compatible, so in this case the DNA fragments can’t be joined. Therefore, answer choice (D) is incorrect.

Not all restriction enzymes make sticky ends. The restriction enzyme Eco R five cuts DNA like this at its recognition sequence. This produces blunt-end cuts, which aren’t as convenient in combining fragments like sticky ends are. Therefore, answer choice (A) is incorrect.

One important feature of recognition sequences is that they are palindromes, meaning they read the same forwards and backwards like the word “racecar.” On the top strand, the sequence reads GAT ATC. And on the bottom strand, in reverse, it also reads GAT ATC. Therefore, the correct answer choice is (B). Restriction enzymes cut at specific nucleotide sequences that are also palindromes.

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