Question:medium
Identify the correct sequence of steps in each cycle of Polymerase Chain Reaction :
Identify the correct sequence of steps in each cycle of Polymerase Chain Reaction :
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Remember the order D-A-E: Denature (Heat), Anneal (Cool), Extend (Synthesize).
Updated On: May 28, 2026
- Annealing → Denaturation → Extension
- Extension → Annealing → Denaturation
- Denaturation → Extension → Annealing
- Denaturation → Annealing → Extension
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question
The goal is to determine the correct chronological order of the three biological steps that take place during a single cycle of the Polymerase Chain Reaction (PCR). PCR is used to amplify millions of copies of a specific DNA segment. Step 2: Key Formula or Approach
PCR logic follows a temperature-driven cycle. - High temp to split the DNA. - Lower temp to stick the primers. - Moderate temp to build the new DNA. The sequence is fixed because you cannot build DNA until the strands are open and the primers are attached. Step 3: Detailed Explanation
Step 1: Denaturation: The double-stranded DNA template is heated to a high temperature (around 94-96$^\circ$C). This heat breaks the hydrogen bonds between the bases, separating the two strands into single-stranded DNA.
Step 2: Annealing: The temperature is lowered to around 40-65$^\circ$C. This allows the two synthetic DNA primers to bind (anneal) to their complementary sequences on the single-stranded DNA templates.
Step 3: Extension: The temperature is raised slightly (usually to 72$^\circ$C), the optimal temperature for {Taq} polymerase. This enzyme adds nucleotides to the primers, extending the chain and completing the synthesis of the new DNA strand.
Step 4: Final Answer
The correct sequence is Denaturation, followed by Annealing, and concluding with Extension. Therefore, (D) is the correct option.
The goal is to determine the correct chronological order of the three biological steps that take place during a single cycle of the Polymerase Chain Reaction (PCR). PCR is used to amplify millions of copies of a specific DNA segment. Step 2: Key Formula or Approach
PCR logic follows a temperature-driven cycle. - High temp to split the DNA. - Lower temp to stick the primers. - Moderate temp to build the new DNA. The sequence is fixed because you cannot build DNA until the strands are open and the primers are attached. Step 3: Detailed Explanation
Step 1: Denaturation: The double-stranded DNA template is heated to a high temperature (around 94-96$^\circ$C). This heat breaks the hydrogen bonds between the bases, separating the two strands into single-stranded DNA.
Step 2: Annealing: The temperature is lowered to around 40-65$^\circ$C. This allows the two synthetic DNA primers to bind (anneal) to their complementary sequences on the single-stranded DNA templates.
Step 3: Extension: The temperature is raised slightly (usually to 72$^\circ$C), the optimal temperature for {Taq} polymerase. This enzyme adds nucleotides to the primers, extending the chain and completing the synthesis of the new DNA strand.
Step 4: Final Answer
The correct sequence is Denaturation, followed by Annealing, and concluding with Extension. Therefore, (D) is the correct option.
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