Question

a) Illustrate the recognition sequence of EcoRI and mention what such sequences are called.
b) How does restriction endonuclease act on a DNA molecule?

Answer 1

Hint: EcoRI is a restriction endonuclease. It is developed from E. coli. Restriction endonuclease is also known as restriction enzyme. It is a protein. The main function of restriction endonuclease is to cut DNA molecules at certain sites and it is used in recombinant DNA technology.

Complete answer:
a) The recognition sequence where EcoRI cleaves the DNA molecule is G/AATTC. Such sequences have a complementary sequence CTTAA/G which is known as a palindromic sequence. Palindromic sequence is observed when the base pairs of the complementary strands of DNA are the same in both directions.

An illustration showing the restriction site for the
Restriction enzyme EcoRI.

b) The restriction endonuclease locates the site where it is about to make a cleavage on the DNA molecule. Once the restriction enzyme recognizes the restriction site it starts the cleavage by the process of hydrolysis. Hydrolysis is the process in which water molecules are added. The restriction endonuclease hydrolyses the bonds of the nearby nucleotides. Thus, the complementary strands are cleaved at certain sites of the DNA. This is how restriction endonuclease acts on a DNA molecule.

Note:
EcoRI is abbreviated as: Eco indicates the micro-organism used in isolating the enzyme− Escherichia coli, R represents the strain of the bacteria−RY-\[13\], \[1\] shows that EcoRI was the first enzyme obtained from this strain. EcoRI recognizes the palindromic sequence G/AATTC on a DNA molecule.