Question

Theoretical number of products formed after \(n\) cycles of PCR per template strand are

• A. \(2^{n}\)
• B. \(n^{10}\)
• C. \(n^{2}\)
• D. \(10^{n}\)

Hint:

Remember the PCR cycle sequence: \[ \boxed{\text{Denaturation} \rightarrow \text{Annealing} \rightarrow \text{Extension}} \] Each cycle ideally doubles the DNA amount. \[ \boxed{\text{DNA after }n\text{ cycles}=2^{n}} \] This exponential amplification is the basis of PCR technology.

Answer 1

The Correct Option is A

Concept: Polymerase Chain Reaction (PCR) is an in vitro technique used to amplify a specific DNA sequence. During every PCR cycle, the amount of DNA approximately doubles because each newly synthesized DNA strand serves as a template in the next cycle.
• PCR was developed by Kary Mullis.
• It consists of three major steps:
• Denaturation
• Annealing
• Extension
• Each cycle ideally doubles the DNA molecules.
• Therefore, DNA amplification follows an exponential pattern.

Step 1: Understand DNA amplification.
Suppose one DNA template molecule is present initially. After each PCR cycle: \[ \begin{aligned} 1^{st}\ \text{cycle} &\rightarrow 2 \\ 2^{nd}\ \text{cycle} &\rightarrow 4 \\ 3^{rd}\ \text{cycle} &\rightarrow 8 \\ 4^{th}\ \text{cycle} &\rightarrow 16 \end{aligned} \] Thus the DNA quantity doubles every cycle.

Step 2: Derive the general formula.
If amplification efficiency is assumed to be 100%, then after \(n\) cycles, \[ \boxed{\text{Number of DNA molecules}=2^{n}} \] For example, \[ 10\ \text{cycles}=2^{10}=1024\ \text{DNA molecules} \] \[ 30\ \text{cycles}=2^{30}\approx1.07\times10^{9}\ \text{copies} \] Hence PCR can generate millions to billions of DNA copies within a few hours.

Step 3: Choose the correct option.
Therefore, \[ \boxed{Option (A) 2^{n} is the correct answer. \]