Which of the following is not required in the preparation of a recombinant DNA molecule?

Concept:

• Recombinant DNA technology is the technique of introducing a desirable gene into the target organism. It alters the genetic composition of the organism.
• A DNA fragment with the desired sequence of the gene from varying sources is introduced via a vector.
• A recombinant DNA molecule is produced by joining together two or more DNA segments. These DNA segments can be from two different organisms.
• The transformed cells in recombinant DNA technology are identified with the help of selectable marker genes like antibiotic resistance genes.

Explanation:

• Option 1: Restriction endonuclease - INCORRECT​
  • Restriction enzymes or restriction endonucleases are the enzymes that cut the phosphodiester bonds in the backbone of the DNA at specific sites.
  • This produces DNA fragments with a known sequence.
  • They cut the DNA molecule at a specific site within a specific palindromic sequence.
  • Restriction endonucleases are used in the preparation of a recombinant DNA molecule to cleave the desired fragment of DNA.
• Option 2: DNA ligase - INCORRECT
  • DNA ligases catalyze the formation of phosphodiester bonds.
  • It is used in repairing single-strand breaks in a DNA molecule.
  • In the preparation of a recombinant DNA molecule, DNA ligase is used to join together DNA fragments.
• Option 3: DNA fragments - INCORRECT
  • In recombinant DNA technology, DNA fragments are produced by cutting DNA by restriction endonucleases.
  • These DNA fragments comprise the desired gene.
  • The DNA fragment is then inserted in the host cell for multiplication.
• Option 4: E. coli - CORRECT
  • E. coli is not required in the preparation of recombinant DNA molecule.
  • E. coli is widely used host organism in recombinant DNA technology.
  • However, it has no practical use in the making of the recombinant DNA molecule.
  • Once this molecule is prepared it is transferred in a host organism like E. coli for the multiplication of the desired gene.
  • Therefore, the E. coli is required after the formation of the recombinant DNA.

So the correct answer is option 4.