The question asks us to arrange the given steps of Polymerase Chain Reaction (PCR) in the correct sequence. PCR is a laboratory technique used to amplify specific DNA sequences.

Understanding the Steps of PCR

PCR involves a series of repeating cycles, each typically consisting of three main steps: denaturation, annealing, and extension. Let's look at the steps listed in the question:

• (A) Denaturation of ds DNA: Double-stranded (ds) DNA is heated to separate it into single strands.
• (B) Annealing: Primers (short DNA sequences) bind to the single-stranded DNA templates.
• (C) Amplification: This refers to the overall process of making many copies of the target DNA sequence over multiple cycles.
• (D) Extension of Primer: DNA polymerase synthesizes new DNA strands starting from the primers.
• (E) Use of DNA polymerase and deoxynucleotides: DNA polymerase is the enzyme that builds the new DNA strands, and deoxynucleotides (dNTPs - dATP, dCTP, dGTP, dTTP) are the building blocks used during extension. These are components needed for the extension step.

Analyzing the Standard PCR Cycle Sequence

In a typical PCR cycle, the sequence of events is:

1. Denaturation: High temperature (\(94-98^{\circ}\text{C}\)) separates the DNA strands.
2. Annealing: Temperature is lowered (\(50-65^{\circ}\text{C}\)) to allow primers to bind to the template DNA.
3. Extension: Temperature is raised (\(72^{\circ}\text{C}\), optimal for Taq polymerase) for the DNA polymerase to synthesize new strands complementary to the template.

This cycle (Denaturation, Annealing, Extension) is repeated 20-40 times, leading to exponential amplification (step C).

Examining the Provided Sequence

The question provides the following sequence of steps (A) through (E). We need to find the option that arranges them correctly. Based on the provided answer, the correct sequence is given as (B), (E), (A), (C), (D). Let's look at this sequence:

1. (B) Annealing
2. (E) Use of DNA polymerase and deoxynucleotides
3. (A) Denaturation of ds DNA
4. (C) Amplification
5. (D) Extension of Primer

Let's interpret this sequence based on the labels provided in the question.

• Starting with (B) Annealing suggests primers are binding. In a standard cycle, this happens after denaturation.
• Next is (E) Use of DNA polymerase and deoxynucleotides. These are the necessary components for synthesizing DNA.
• Following is (A) Denaturation of ds DNA, which is the first step in separating the DNA strands.
• Then comes (C) Amplification, which is the overall process outcome over multiple cycles.
• Finally, (D) Extension of Primer, where new DNA strands are built.

While the standard PCR cycle is Denaturation → Annealing → Extension, the sequence provided by option (b) is (B), (E), (A), (C), (D). Following the instruction to provide the solution based on the given correct answer, we present this sequence as described by the step labels.

Arranging the steps according to the sequence (B), (E), (A), (C), (D) as indicated by the option means we consider this specific order for the listed items.

Revision Table: Key PCR Concepts

Additional Information: Components of a PCR Reaction

A typical PCR reaction mixture contains several key components:

• DNA Template: The DNA containing the target sequence to be amplified.
• Primers: Short, synthetic DNA sequences complementary to the regions flanking the target sequence. Two primers are needed, one for each strand.
• DNA Polymerase: A heat-stable enzyme, such as Taq polymerase, that synthesizes new DNA.
• Deoxynucleotides (dNTPs): The four DNA building blocks (dATP, dCTP, dGTP, dTTP).
• Buffer Solution: Provides a stable chemical environment for the enzyme activity, usually containing salts like \( \text{MgCl}_2 \).
• Ions: Magnesium ions (\( \text{Mg}^{2+} \)) are essential cofactors for DNA polymerase activity.

These components are mixed in a tube and placed in a thermocycler, which controls the precise temperature changes required for denaturation, annealing, and extension in cycles.