Question
Read the following and answer any four questions from 2(i) to 2(v) given below:

Restriction endonuclease was isolated for the first ti me by W. Arb er in 1962 in bacteria. Restriction endonucleases cut the DNA duplex at specific points therefore they are also called as molecular scissors or biological scissors. Three types of restriction endonucleases are Type I, Type II and Type III but only Type II restriction endonucleases are used in recombinant DNA technology. Restriction endonuclease EcoR I recognises the base sequence GAATTC in DNA duplex and cut strands between G and A.

  1. Only type II restriction enzymes are used in gene manipulation because
  1. ATP is not required for cleaving.
  2. It consists of three different subunits.
  3. It makes cleavage or cut in both the strands of DNA molecule.
  4. Both (a) and (c).
  1. Which of the following ions are used by restriction endonucleases for restriction?
  1. Mg2+ ions
  2. Mn2+ ions
  3. Na2+ ions
  4. K2+ ions
  1.  Restriction endonuclease was isolated for the first time in a:
  1. Plant cell.
  2. Animal cell.
  3. Prokaryotic cell.
  4. Genninal cell.
  1. Restriction endonucleases are also called as molecular or biological scissors because,
  1. They cleave base pairs of DNA only at their terminal ends.
  2. They cleave one or both the strands of DNA.
  3. They act only on single stranded DNA.
  4. None of these.
  1. Select the option that correctly states the working action of restriction endonuclease EcoR I on DNA sequence GAATTC
  1. $\ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  2. $ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  3. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \uparrow$

  4. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

Answer

  1. (d) Both (a) and (c).

Explanation:

Only type II restriction enzymes are used in gene manipulation for two reasons : (a) No ATP is required for the cleaving action. (b) It makes cleavage or cut in both the strands of DNA molecule. 

  1.  (a) Mg2+ ions

Explanation:

All the three types ofrestrictionendonucleases require Mg2. ions for restriction.

  1.  (c) Prokaryotic cell.

Explanation:

Restriction endonuclease was isolated for the first time by W. Arber in 1962 in bacteria. 

  1.  (b) They cleave one or both the strands of DNA.

Explanation:

In 1972, Paul Berg was able to introduce a gene of SV-40 virus into a bacterium with the help of lambda phage. 

  1.  (b) $ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

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