Which is not a step of PCR ?
**Core Concept**
Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify specific DNA sequences. It involves multiple cycles of denaturation, annealing, and extension to produce millions of copies of the target DNA sequence. Understanding the steps involved in PCR is crucial for its accurate interpretation and application in various fields.
**Why the Correct Answer is Right**
The correct answer to this question will be the step that is not a part of the standard PCR protocol. PCR typically involves the following steps:
* Denaturation: The double-stranded DNA is heated to separate the two strands, making them available for amplification.
* Annealing: The temperature is lowered to allow the primers to bind to the target DNA sequence.
* Extension: The temperature is raised to allow the DNA polymerase to synthesize new DNA strands, extending the primers.
* Hybridization: The newly synthesized DNA strands are then used as templates for the next cycle of amplification.
**Why Each Wrong Option is Incorrect**
**Option A:** Denaturation is a fundamental step in PCR, as it allows the double-stranded DNA to be separated into single strands, making them available for amplification. This option is incorrect because it is a crucial step in the PCR protocol.
**Option B:** Hybridization is a part of the PCR protocol, where the newly synthesized DNA strands are used as templates for the next cycle of amplification. This option is incorrect because it is an essential step in the PCR process.
**Option C:** Extension is the step where the DNA polymerase synthesizes new DNA strands, extending the primers. This option is incorrect because it is a key component of the PCR protocol.
**Clinical Pearl / High-Yield Fact**
One of the most common pitfalls in PCR is contamination with external DNA, which can lead to false-positive results. To minimize this risk, it is essential to use proper laboratory protocols, including the use of sterile equipment and negative controls.
**Correct Answer: D.**