Problem 5 What are the different steps inv... [FREE SOLUTION]

Chapter 6: Problem 5

What are the different steps involved in one cycle of a PCR reaction?

Short Answer

Expert verified

PCR cycle consists of Denaturation, Annealing, and Extension.

Step by step solution

Denaturation

This is the first stage of the PCR cycle where the double-stranded DNA is heated to around 94-98掳C. This high temperature causes the hydrogen bonds between the two strands to break, resulting in the separation of the DNA into two single strands. This denaturation is crucial because it provides single-stranded templates for the subsequent step.

Annealing

After denaturation, the reaction temperature is lowered to around 50-65掳C. This cooling allows DNA primers to bind (anneal) to complementary sequences on the single-stranded DNA templates. Primers are short DNA sequences that initiate DNA synthesis from a nucleotide substrate.

Extension (or Elongation)

In this stage, the temperature is raised to around 72掳C. At this temperature, Taq polymerase (a DNA polymerase enzyme commonly used in PCR) synthesizes a new DNA strand by adding nucleotide bases to the annealed primer, effectively creating a new complementary DNA strand.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Denaturation

Denaturation is the first step in the polymerase chain reaction (PCR) cycle. During this critical stage, the double-stranded DNA is subjected to high temperatures, typically between 94-98掳C. The purpose of this step is to break the hydrogen bonds that hold the two strands of DNA together.

This separation is essential as it yields two single-stranded DNA templates for replication.
Without denaturation, the subsequent steps of PCR could not proceed, as the enzyme machinery requires single-stranded DNA to initiate synthesis.

The denaturation forms the foundation for allowing primers, small complementary sequences, to bind during the next stage of PCR.

Annealing

Following denaturation, the PCR cycle proceeds to the annealing phase. In this step, the reaction temperature is delicately reduced to approximately 50-65掳C. This cooling mechanism is crucial as it enables primers to attach or "anneal" to their complementary sequences on the separated single-stranded DNA.

Primers are short chains of nucleotide sequences that act like bookmarks, directing the Taq polymerase where to begin DNA synthesis.
The precision of the annealing temperature is critical: too high, and the primers won't bind; too low, and non-specific binding may occur.

This step ensures that the DNA polymerase has a specific start point for synthesizing new DNA strands in the following phase.

Extension

Extension, also known as elongation, is the final critical step in a PCR cycle. Here, the reaction mixture is heated to around 72掳C, the optimal working temperature for Taq polymerase. This enzyme is tasked with synthesizing a new strand of DNA by adding nucleotide bases to the primer-bound sites.

Taq polymerase is a thermostable enzyme isolated from the bacterium *Thermus aquaticus*, which thrives in hot environments, making it ideal for PCR.
During this stage, the enzyme "reads" the template strand and matches each nucleotide with its complementary base, producing an exact copy of the original DNA strand.

The completion of this step generates new double-stranded DNA molecules, effectively doubling the DNA content and enabling exponential amplification with each consecutive PCR cycle.

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91影视

What are the different steps involved in one cycle of a PCR reaction?

Short Answer

Step by step solution

Denaturation

Annealing

Extension (or Elongation)

Key Concepts

Denaturation

Annealing

Extension

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