EcoR1 and HindIII are two different restriction enzymes. If the DNAs of differen

Question

            EcoR1 and HindIII are two different restriction enzymes. If the DNAs of different organisms are cut as described below, which DNAs could NOT join together and be permanently sealed?

a.         Human DNA cut with EcoR1/ chimp DNA cut with EcoR1

b.         Prokaryotic DNA cut with HindIII/ eukaryotic DNA cut with HindIII

c.         Mouse liver DNA cut with EcoR1/ mouse kidney DNA cut with EcoR1

d.         Mouse DNA cut with HindIII/ chimp DNA cut with HindIII

e.         Bacterial DNA cut with EcoR1/ mouse DNA cut with HindIII

Explanation / Answer

The answer is- e. Bacterial DNA cut with EcoR1/mouse DNA cut with HindIII

Restriction enzymes, are the bacterial enzymes which cut the double-stranded DNA into fragments based on specific nucleotides recognition and they are also known as the molecular scissors.

EcoR1 and HindIII are two such Restriction enzymes which recognise a particular sequence and make a cut at the site which is known as the Restriction site. EcoR1 is from bacteria Escherichia coli and HindIII from Haemophilus influnzae which forms sticky ends after the enzyme cut at restriction site. The sequence they recognise are palindromic sequences which are same if read it in any frame (5'-3' or 3'-5').

For e.g., NITIN

Recognition sequence for EcoR1 - GAATTC

And for HindIII - AAGCTT

When the DNA is cut using same restriction enzyme, on same or different organism. The sticky ends formed will be the same and a fragment of one can join to the sticky end of the other. Then these fragments of DNA when binds with the sticky ends, the final nick is joined using ligase (used for sealing).

This technique of Restriction enzymes is very helpful in biotechnology for forming recombinant DNA.

Lets look on the options one by one:

a. Human DNA and chimp DNA both were cut using same Restriction enzyme EcoR1 which will form same sticky ends and the DNAs can be joined.

b. Prokaryotic DNA and eukaryotic DNA cut using HindIII even though these are different DNA but when cut using same restriction enzyme. The recombinant DNA could be formed.

c. Mouse Liver DNA with mouse kidney DNA, the DNA fragments can be joined when the both DNA were cut using same Restriction enzyme (EcoR1).

d. Mouse DNA with chimp DNA using HindIII. The different organsims DNA fragments can be joined using same Restriction enzyme to cut both organism and then joining using ligase to permanently seal them.

e. Bacterial DNA cut with EcoR1 cannot be joined with mouse DNA cut from HindIII because both enzymes recognises different Restriction sites with different palindrome sequences that will produce different sticky ends so, there will be no binding at the sticky ends and DNAs could not be joined and sealed together.

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