PCR employs in vitro DNA replication. DNA replication in vivo-i.e., in a cell, normally requires helicase activity. However, during the PCR reaction, we do not need helicase. Why? Make sure you include which PCR step replaces helicases function.

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**PCR and the Role of Helicase in DNA Replication**

**Question:**
PCR employs *in vitro* DNA replication. DNA replication *in vivo*—i.e., in a cell, normally requires helicase activity. **However, during the PCR reaction, we do not need helicase. Why? Make sure you include which PCR step replaces helicase's function.**

**Explanation:**
In cellular DNA replication (*in vivo*), helicase is an essential enzyme that unwinds the DNA double helix, allowing each strand to be copied. This unwinding is crucial for the replication machinery to access the DNA template.

In contrast, during the Polymerase Chain Reaction (PCR), which is an *in vitro* method of DNA replication, the function of helicase is replaced by a step involving thermal cycling. The high temperature of the denaturation step (usually around 94-98°C) in PCR causes the DNA double helix to separate into single strands, effectively mimicking the unwinding activity of helicase without the need for the enzyme. This allows the DNA polymerase to access and replicate each strand.
Transcribed Image Text:**PCR and the Role of Helicase in DNA Replication** **Question:** PCR employs *in vitro* DNA replication. DNA replication *in vivo*—i.e., in a cell, normally requires helicase activity. **However, during the PCR reaction, we do not need helicase. Why? Make sure you include which PCR step replaces helicase's function.** **Explanation:** In cellular DNA replication (*in vivo*), helicase is an essential enzyme that unwinds the DNA double helix, allowing each strand to be copied. This unwinding is crucial for the replication machinery to access the DNA template. In contrast, during the Polymerase Chain Reaction (PCR), which is an *in vitro* method of DNA replication, the function of helicase is replaced by a step involving thermal cycling. The high temperature of the denaturation step (usually around 94-98°C) in PCR causes the DNA double helix to separate into single strands, effectively mimicking the unwinding activity of helicase without the need for the enzyme. This allows the DNA polymerase to access and replicate each strand.
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