A 200 µl of polymerase chain reaction has 100 template DNA molecules and the reaction was performed for 10 cycles.
Q.54 How many molecules of amplicons will be generated?
PCR Amplicons Calculation: 100 Templates 10 Cycles Yield 1.024 × 10⁵ Molecules
PCR amplification theoretically doubles the number of target DNA molecules each cycle, so starting with 100 template DNA molecules after 10 cycles yields 100 × 2¹⁰ amplicons. Since 2¹⁰ = 1024, the total is 102,400 molecules, or 1.024 × 10⁵, matching option (B).
🔬 PCR Calculation Breakdown
The formula for amplicons in PCR is N = N₀ × 2ⁿ, where N₀ is initial templates (100) and n is cycles (10).
Calculate 2¹⁰ step-by-step:
- 2¹ = 2
- 2² = 4
- 2³ = 8
- 2⁴ = 16
- 2⁵ = 32
- 2⁶ = 64
- 2⁷ = 128
- 2⁸ = 256
- 2⁹ = 512
- 2¹⁰ = 1024
Thus, 100 × 1024 = 102,400 = 1.024 × 10⁵ (ignores inefficiencies like incomplete extension).
✅ Option Analysis
| Option | Value | Calculation Error | Status |
|---|---|---|---|
| (A) 1.024 × 10⁴ | 10,240 | 100 × 2⁸ (8 cycles) | ❌ Incorrect |
| (B) 1.024 × 10⁵ | 102,400 | 100 × 2¹⁰ (exact) | ✅ CORRECT |
| (C) 2.048 × 10⁴ | 20,480 | 200 × 2⁸ (wrong N₀) | ❌ Incorrect |
| (D) 2.048 × 10⁵ | 204,800 | 100 × 2¹¹ (11 cycles) | ❌ Incorrect |
📈 Step-by-Step 10-Cycle Doubling
N = 100 × 2¹⁰
- Cycle 0: 100 molecules
- Cycle 1: 200
- Cycle 2: 400
- Cycle 3: 800
- Cycle 4: 1,600
- Cycle 5: 3,200
- Cycle 6: 6,400
- Cycle 7: 12,800
- Cycle 8: 25,600
- Cycle 9: 51,200
- Cycle 10: 102,400
🧪 Practical PCR Considerations
- Efficiency: <100% reduces yield; 10 cycles stay near ideal (~90-100%)
- Plateau Phase: Actual yields drop after 25-35 cycles due to reagent limits
- Validation: Use qPCR for precise biotech work
- Exam Relevance: Matches GATE biotechnology exam pattern
