Assuming 100% reaction efficiency, how many copies of dsDNA containing the amplicon will be
present in the polymerase chain reaction mixture after 25 cycles?
1. 2 power 25
2. 252
3. 25 × 2
4. 2525

 

How Many Copies of dsDNA Are Produced After 25 PCR Cycles?

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Introduction to PCR and DNA Amplification

Polymerase Chain Reaction (PCR) is a powerful molecular biology technique used to amplify specific DNA sequences. It allows the exponential replication of a target DNA segment through repeated cycles of denaturation, annealing, and extension. PCR is widely used in research, diagnostics, forensic science, and biotechnology due to its high sensitivity and specificity.

In this article, we will calculate how many copies of double-stranded DNA (dsDNA) containing the amplicon will be present after 25 PCR cycles, assuming 100% reaction efficiency.

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✅ Key Phrase: PCR Cycle Amplification Calculation

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✅ Question and Answer

Question:
Assuming 100% reaction efficiency, how many copies of dsDNA containing the amplicon will be present in the polymerase chain reaction (PCR) mixture after 25 cycles?

1. 2252^{25}225
2. 252
3. 25 × 2
4. 2525

Correct Answer: ✔️ Option 1 

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Understanding the Principle of PCR

PCR is based on the principle of exponential amplification of DNA. The process involves three main steps:

1. Denaturation

• The double-stranded DNA is heated to around 94–98°C to separate it into two single strands.

2. Annealing

• The temperature is lowered to 50–65°C to allow primers to bind to the single-stranded DNA template.

3. Extension

• DNA polymerase synthesizes new complementary DNA strands at 72°C by adding nucleotides to the primers.

✅ Exponential Amplification Formula:

The number of DNA copies produced after n cycles of PCR is given by the formula:

N=N0×2 Power n 

Where:

• N = Final number of DNA copies
• N₀ = Initial number of DNA copies (starting template)
• n = Number of cycles