All of the following are correct regarding the polymerase chain reaction (PCR) EXCEPT:

Question

Accepted Answer

B. PCR requires a single primer that binds to both strands of the target DNA. ## PCR Fundamentals

**Key Point:** PCR requires TWO primers (forward and reverse), not one. Each primer binds to a different strand of the target DNA and extends in opposite directions, creating the exponential amplification characteristic of PCR.

### Why Each Statement Is True (Except One)

| Feature | Correct Statement |
|---------|-------------------|
| **Taq Polymerase** | Thermostable enzyme derived from *Thermus aquaticus*; remains active at 94–95°C (denaturation) and 72°C (extension) |
| **Temperature Cycling** | Annealing (50–65°C) < Extension (72°C) < Denaturation (94–95°C) |
| **Primer Design** | **Two primers required** — one for each strand; bind to opposite ends of target region |
| **Amplification** | Exponential (2^n) because each new strand becomes a template; 30 cycles ≈ 10^9-fold amplification |

### The Trap: Single vs. Dual Primer

**High-Yield:** A single primer would only amplify one strand linearly (linear amplification, not exponential). PCR's power comes from the **complementary primer pair** creating a defined amplicon bounded by the two primer sites.

**Mnemonic:** **TAPS** = **T**aq, **A**nnealing < Extension, **P**rimer pair (×2), **S**trands (both amplified).

[cite:Molecular Cloning: A Laboratory Manual 4e, Ch 3]

Answer

A. Exponential amplification of target DNA occurs because each newly synthesized strand serves as a template in subsequent cycles

Answer

C. The annealing temperature is typically lower than the extension temperature in each cycle

Answer

D. Taq polymerase is thermostable and remains active at temperatures above 90°C

All of the following are correct regarding the polymerase chain reaction (PCR) EXCEPT:

Explanation

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