Question

The first restriction endonuclease isolated was
(a) EcoRI
(b) Bam HI
(c) SalI
(d) Hind II

Answer 1

Restriction endonuclease serves as molecular scissors for cutting down the DNA into discrete reproduced fragments. They cut DNA at defined sites and are one of the most important groups of enzymes for the manipulation of DNA. The term was coined by Lederberg and Messelson in 1964. These are found in bacterial cells, where they function as a part of a protective mechanism called restriction-modification system.

Complete step by step answer:
Hind II is the first restriction endonuclease isolated. A restriction endonuclease is a group of enzymes that recognize specific nucleotide sequences in DNA often 4 or 6 base pairs long and cut both strands of DNA within recognition sites. Different endonucleases found in different bacteria recognize nucleotide sequences and therefore cut DNA at different cleavage sites. Restriction enzymes are classified into two classes. Class 1 consists of type II enzymes. Class II enzymes consist of type I and type II enzymes. HindII was the first restriction enzyme to be isolated. This enzyme was first isolated from Haemophilus influenzae Rd strain II. So, the enzyme was shorts labeled as HindII. Each enzyme is named by a three- letter code in italics. The first letter of the name is the name of the genus in which a given enzyme is discovered is written in capital letters The second and third letters are from the species name. This is followed by the strain name. If a particular strain has more than one restriction enzyme these will be identified by Roman numerals as |,||, |||, etc. A general name endonuclease R may be added. Example; Eco RI enzyme is derived from Escherichia coli carrying antibiotic resistance plasmid RI.
So, the correct answer is '(d) Hind II'

Additional Information:
- Enzymes such as EcoR1 and Pst 1 generate DNA fragments with sticky or cohesive ends, as the protruding sequence can be base pair with complementary sequences generated by the same enzyme.
- Thus by cutting two different DNA samples with the same enzyme and mixing the fragments together, recombinant DNA can be produced.
- this one of the most important applications of restriction Enzymes.

Note:
- Type II endonucleases are widely used for mapping and reconstructing DNA in vitro because they recognize specific sites and cleave just at these sites.
- These enzymes are found in bacteria and archaea and provide a defense mechanism against invading viruses.
- Inside a prokaryote, the restriction enzymes selectively cut up foreign DNA in a process called restriction digestion; meanwhile, host DNA is protected by a modification enzyme that modifies the prokaryotic DNA and blocks cleavage. Together, these two processes form the restriction- modification system.
- Werner Arber, Hamilton Smith, and Daniel Nathans received the 1978 Nobel Prize in Physiology or Medicine for developing the smaller names for the restriction enzymes.