Question

Write about various types of restriction enzymes.

Answer 1

Restriction enzymes or restriction endonuclease are the proteins that are produced by the bacteria that cleaves or divides the DNA at a specific site along the molecule. Restriction enzymes cleave foreign DNA in the bacterial cell and eliminate the infecting organism. These enzymes can be isolated from the bacterial cells to be used in the labs for the manipulation of DNA fragments.

Complete answer:
Molecular biologists Werner Arber, Hamilton Smith, and Daniel Nathans discovered and characterized the restriction enzymes in the late 1960s and early 1970s.
Restriction enzymes are those enzymes that cleave the DNA at a particular site along the molecule.

Various types of restriction endonucleases are:
- Type I Enzymes
- Type II Enzymes
- Type III Enzymes
- Type IV Enzymes

- Type I Enzymes: These enzymes are multi-subunit complexes and combination of restriction and modification enzymes that cleave DNA at random far from there recognition sequence.
- Type II Enzymes: These enzymes cleave DNA at specific positions close to two or within their recognition sequence. These enzymes are the only type that is used in the laboratory for daily DNA analysis and gene cloning. For example, Hhal, HindIII, and Notl.
- Type III Enzymes: These enzymes are similar to the type I enzymes.
- Type IV Enzymes: These are the enzymes that cleave the methylated DNA only and have weaker sequence specificity.

Hence, the correct answer is option (B).

Additional information:
Restriction enzymes are used by the bacterium to fight against a bacterial virus called bacteriophages or phages. The names of the restriction enzymes come from the genus, species, and the strain of the bacteria from which it is produced. For example, the EcoRI enzyme produced by E. coli strain RY13.

An enzyme simply is a substance that catalyzes and regulate the rate of a chemical reaction and itself remains unaltered in the process.
It is believed that restriction enzymes originated from the ancient protein and evolved to recognize a particular sequence through gene amplification and genetic recombination.

Note: Restriction enzymes are the enzymes that cut the DNA at the specific site along the molecule. Restriction enzymes recognize the specific and short sequence of nucleotide bases, these regions are called recognition sequences or recognition sites and are distributed randomly throughout the DNA. Restriction enzymes are categorized into four types on the basis of difference in the cleavage site, structure, cofactors, and specificity. Type I enzymes and type II enzymes are similar activities. Restriction enzymes protect foreign genetic material.