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What are the three steps of polymerase chain reaction (PCR), and at what temperatures do these occur?

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Final answer:

The Polymerase Chain Reaction (PCR) consists of three main steps performed at specific temperatures: denaturation at 94°C to 96°C, annealing at 68°C, and extension at 72°C, which is enabled by the heat-stable enzyme Taq polymerase.

Step-by-step explanation:

The Polymerase Chain Reaction (PCR) is a technique used to amplify DNA sequences exponentially. It involves three primary steps: denaturation, annealing, and extension.

  • Denaturation: During this step, the double-stranded DNA is heated to high temperatures of 94°C to 96°C, causing the hydrogen bonds between the DNA strands to break and resulting in two single strands of DNA.
  • Annealing: The temperature is then lowered to 68°C to allow short DNA segments called primers to anneal, or attach, to their complementary sequences on the single-stranded DNA templates.
  • Extension: The temperature is raised to 72°C to enable the heat-stable enzyme Taq polymerase to add nucleotides to the primers, extending the DNA strand and creating new DNA fragments.

These steps are repeated for 20-30 cycles in a thermal cycler, which can precisely control the temperatures required for each step. After multiple cycles, a significant number of DNA copies, all with the targeted length, are obtained.

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