Most common enzymatic tool in genetic engineering-
Correct Answer: Restriction endonuclease
Description: Ans. is 'd' i.e., Restriction endonuclease o At the heart of genetic engineering is the ability to cut DNA molecules at precisely defined sites, o This is usually done with purified bacterial enzyme, the restrication endonuclease.o Restriction endoncleases were called restriction enzymes because their presence in a given bacterium restricted the growth of foreign (non-bacterial) DNA, e g. bacteriophages, o Restriction endonuclease (also called restrition enzyme) cut DNA at specific DNA sequence within the molecule in a sequence specific manner. The site cleaved by restriction endonuclease is called its restriction siteo These enzymes recognize certain palindromic sequences in the DNA, ie. the short sequence (4-7 base pairs) which has got two fold rotational symmetry. In simple language, a short sequence (4-7 bp) of duplex DNA that is same when two strands are read in opposite direction is called palindrome.o Palindrome serves as the target for most restriction endonucleases. Each restriction enzyme (restriction endonuclease) recognizes specific nucleotide sequence, ie. each restriction enzyme has specific palindromic sequence to recognizeo Restriction endonucleases cleave (cut) both strands of DNA.o Some restriction enzymes cut both strand at same level, so as to leave no unpaired bases on either end. These ends are called blunt ends.o On the other hand, some restriction enzyme cut two strands in staggered manner, leaving two to four nucleotides of one strand unpaired at each end. Thses ends are referred to as cohesive ends (or sticky ends or staggered ends).o Sticky ends are particularly useful in constructing hybrid (or chimeric) DNA molecule. Restriction fragments of different DNAs can base pair with each other if they have sticky ends which are complementary. Therefore two unrelated DNA fragments can base pair with each other, if they were cleaved by the same restriction endonucleases (because each restriction endonuclease cuts same and specific palindromic sequence on diferent DNAs).
Category:
Biochemistry
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