Question

Following are the steps involved in the process of PCR.
a. Annealing
b. Amplification (~1 billion times)
c. Denaturation
d. Treatment with Taq polymerase and deoxynucleotides
e. Extension
Choose the correct sequence of steps of PCR from the options given below :

• A. c → a → d → e → b
• B. a → b → e → d → c
• C. a → c → e → d → b
• D. d → b → e → c → a

Answer 1

The Correct Option is A

Polymerase Chain Reaction (PCR) is a widely used method in molecular biology to amplify segments of DNA. The process follows a specific sequence of steps, each of which is crucial for the successful amplification of the target DNA. Let's analyze the steps of PCR:

1. Denaturation: This is the first step in the PCR process. The DNA is heated to around 94°C to 98°C to separate the double-stranded DNA into single strands by breaking the hydrogen bonds between the bases.
2. Annealing: The temperature is lowered to approximately 50°C to 65°C, allowing primers to attach to the single-stranded DNA. Primers are short sequences of nucleotides that provide a starting point for DNA synthesis.
3. Treatment with Taq Polymerase and Deoxynucleotides: The DNA polymerase enzyme, specifically Taq polymerase, is added along with deoxynucleotide triphosphates (dNTPs). Taq polymerase is a thermostable enzyme that synthesizes new DNA strands by adding nucleotides.
4. Extension: The temperature is increased to around 72°C, which is the optimal working temperature for Taq polymerase. The enzyme extends the primers to form a new DNA strand by adding complementary nucleotides.
5. Amplification (~1 billion times): These steps are repeated for 25-35 cycles, exponentially increasing the amount of DNA. After repeated cycles, the target DNA sequence is amplified approximately one billion times.

Based on this description, the correct sequence of steps for the PCR process is:

1. Denaturation (c)
2. Annealing (a)
3. Treatment with Taq Polymerase and Deoxynucleotides (d)
4. Extension (e)
5. Amplification (~1 billion times) (b)

Thus, the correct option is c → a → d → e → b.

This sequence ensures that each DNA strand is duplicated during each cycle, resulting in the exponential growth of the target DNA segment.