Question

The basic scheme of the essential steps involved in the process of recombinant DNA technology is summarised below in the form of a flow diagram. Study the given flow diagram and answer the questions that follow: \begin{center} Step-1 \quad Plasmid DNA (cut using Restriction Enzyme EcoR I) \quad + \quad Foreign DNA (cut using Restriction Enzyme EcoR I)
$\downarrow$
DNA ligase
$\downarrow$
Step-2 \quad Recombinant DNA molecule
$\downarrow$
Step-3 \quad Transfer of recombinant DNA molecule to the host cell
$\downarrow$
Step-4 \quad Replication of recombinant DNA molecule in the host cell \end{center} (a) Name the specific enzyme that might have been used to make the multiple copies of foreign DNA before undergoing Step-1 of the process.
(b) How does the use of restriction enzyme EcoR I in Step-1 facilitate the action of DNA ligase to form the recombinant DNA molecule? Explain.
(c) Name the most commonly used host in the above process.

Hint:

PCR uses DNA polymerase to amplify DNA. EcoR I generates sticky ends, and DNA ligase seals the DNA strands. E. coli is the standard host in rDNA technology.

Answer 1

Step 1: (a) The enzyme used to make multiple copies of foreign DNA is DNA polymerase, specifically Taq polymerase during the PCR (Polymerase Chain Reaction) process.
Step 2: (b) EcoR I creates sticky ends (overhanging sequences) in both plasmid and foreign DNA.

• These sticky ends are complementary, allowing the foreign DNA to bind with the plasmid DNA.
• DNA ligase then joins the sugar-phosphate backbones, forming a stable recombinant DNA molecule.

Step 3: (c) The most commonly used host is Escherichia coli (E. coli).