Question

How would you explain the mechanism of action of restriction enzymes?

Answer 1

Hint: The restriction enzymes belong to the class of enzymes which are isolated from bacteria. They are known to cut DNA , molecule in a special fashion. These enzymes since isolated have been an important tool for recombinant DNA (rDNA) technology.

Complete answer:
The restriction enzymes can act on a specific sequence by recognizing a recognition sequence which is specific in its base sequence. the restriction enzyme produces a double-stranded cut. The recognition sequences can be classified based on the number of bases it has, the number of bases usually varies between 4 and 8 bases, and this determines this sequence will appear in genome e.g., a 4-base pair sequence would theoretically occur once every 44 or 256bp. This sequence is palindromic, which means that it reads the same either way. Theoretically, there are two types of palindromic sequences present in DNA.

1)The mirror-like palindrome which is similar to those which are found in a way where the sequence reads similar as forward and backwards. e.g. GTA ATG.
2)The inverted repeat palindrome still reads the same forward and backwards, but in complementary DNA strands (i.e., double-stranded DNA) as in GTATAC, the forward and backward sequences are found (GTATAC being complementary to CATATG). Inverted repeat palindromes are more frequent and biologically more important than mirror-like palindromes.

Note: 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 (a methyltransferase) that modifies the prokaryotic DNA and blocks cleavage. Together the constraint alteration mechanism is created by these two methods.