Enzyme ‘Taq polymerase’ used in PCR, has been isolated from bacteria

A) Agrobacterium tumefaciens

B) Thermus aquaticus

C) Streptomyces albus

D) Escherichia coli

Polymerase Chain Reaction (PCR) is a widely used biological technique in molecular biology to make multiple copies of a specific DNA fragment. The core principle behind PCR is enzymatic replication of DNA, which involves amplifying a short segment of DNA using primer-mediated enzymes. The enzyme primarily responsible for this process is DNA polymerase.

Components Required for PCR:

• DNA Template: The DNA sequence to be amplified.
• DNA Polymerase: Typically, Taq polymerase is used, which is heat-resistant and obtained from the bacterium Thermus aquaticus.
• Oligonucleotide Primers: Short DNA segments that are complementary to the 3' ends of the sense and antisense strands.
• Deoxyribonucleotide Triphosphates (dNTPs): These provide the energy required for the reaction.
• Buffer System: Ensures the stability and activity of the polymerase enzyme.

Steps Involved in PCR:

PCR involves three main steps:

1. Denaturation:
   • The reaction mixture is heated to 94°C for 1-2 minutes.
   • This heating breaks the hydrogen bonds between the two strands of DNA, resulting in single-stranded DNA templates for amplification.
2. Annealing:
   • The temperature is lowered to 54-60°C for 20-40 seconds.
   • The primers bind to their complementary DNA sequences at the 3' ends of both the sense and antisense strands.
3. Elongation:
   • The temperature is raised to 72-80°C, and Taq polymerase enzyme extends the DNA strands in the 5' to 3' direction.
   • Taq polymerase is stable at high temperatures and adds the complementary nucleotides to form a new strand, creating a double-stranded DNA molecule.

After repeating these steps multiple times, a large number of DNA copies are produced in a short period.

Conclusion: PCR is a powerful and efficient method for amplifying specific DNA sequences, making it an invaluable tool in molecular biology.

So, the correct answer is option (B).