Tools of Biotechnology: Restriction Endonucleases - Practice Questions & MCQ

• These are also known as molecular scissors, used for cutting DNA. 
• The cutting of DNA at specific locations became possible with the discovery of molecular scissors, i.e., restriction enzymes.
• Restriction endonuclease was isolated for the first time by W. Arber in 1962 in bacteria. 
• In 1970, Hamilton O. Smith, Thomas Kelly and Kent Wilcox isolated and characterized the first type II restriction enzyme, Hin d II, from the bacterium Haemophilus influenzae.
• Restriction enzymes belong to a larger class of enzymes called nucleases, which are of two types:
  • Exonucleases remove nucleotides from the ends of the DNA either (5′ or 3′) in one strand of the duplex.
  • Endonucleases make cuts at specific positions within DNA. Each restriction endonucleases function by ‘inspecting’ the length of a DNA sequence.

Naming of Restriction Enzymes:

• The convention for naming these enzymes proceeds in a way that:
  • The first letter of the name comes from the genes
  • The second two letters come from the species of a prokaryotic cell, from which they were isolated
  • Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria

Types of Restriction Endonucleases:

• Type I Restriction Endonucleases: These enzymes consist of three different subunits. They require ATP, Mg2+., and S-adenosyl methionine for restriction. These are not used in recombinant DNA technology.
• Type II Restriction Endonucleases: These are the simple endonucleases that require Mg2+ for their functioning. No ATP is needed for their cleaving action and they make cuts in both the strands of the DNA. These are the only types of restriction endonucleases that are used in recombinant DNA technology.
• Types III Restriction Endonucleases: These have intermediate properties between type I and type II.