The polymerase chain reaction (PCR) is used by se quantity of DNA is very small, mixed, or contamin the how PCR works using a diagram to help illustra illustrate your point).

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**Understanding Polymerase Chain Reaction (PCR)**

Polymerase chain reaction (PCR) is a powerful technique used by scientists to amplify DNA sequences. It is especially useful when the quantity of DNA is very small, mixed, or contaminated with other organisms. Below is an explanation of how PCR works, illustrated through a series of steps.

### Steps of PCR:

#### 1. Denaturation:
   - The double-stranded DNA is heated to around 94-98°C. 
   - This high temperature causes the hydrogen bonds between the DNA strands to break, resulting in two single strands.

#### 2. Annealing:
   - The temperature is lowered to around 50-65°C.
   - Short DNA sequences called primers bind (or anneal) to the complementary sequences on the single-stranded DNA templates.

#### 3. Extension:
   - The temperature is raised to around 72°C.
   - Taq polymerase (a heat-stable enzyme) attaches to the primers and starts adding nucleotides to the 3’ end of each primer, synthesizing new DNA strands complementary to the original template strands.

### PCR Cycle Illustration:

Each PCR cycle involves three steps: Denaturation, Annealing, and Extension. These steps are repeated multiple times (typically 25-35 cycles), leading to exponential amplification of the target DNA sequence. Here is the detailed process for three cycles:

#### **Cycle 1:**
   - **Denaturation:** The DNA is heated to 94-98°C, separating it into single strands.
   - **Annealing:** The temperature is lowered to 50-65°C, allowing primers to bind to the single-stranded DNA.
   - **Extension:** The temperature is raised to 72°C, and Taq polymerase synthesizes new strands, resulting in two double-stranded DNA molecules from the original one.

#### **Cycle 2:**
   - **Denaturation:** The two double-stranded DNA molecules are heated again to separate into single strands.
   - **Annealing:** Primers bind to the new single-stranded templates.
   - **Extension:** Taq polymerase synthesizes new DNA, resulting in four double-stranded DNA molecules.

#### **Cycle 3:**
   - **Denaturation:** The four double-stranded DNA molecules are heated to separate into single strands.
   - **Annealing:** Primers bind to these new single-stranded templates.
   - **Extension:** Taq polymerase
Transcribed Image Text:**Understanding Polymerase Chain Reaction (PCR)** Polymerase chain reaction (PCR) is a powerful technique used by scientists to amplify DNA sequences. It is especially useful when the quantity of DNA is very small, mixed, or contaminated with other organisms. Below is an explanation of how PCR works, illustrated through a series of steps. ### Steps of PCR: #### 1. Denaturation: - The double-stranded DNA is heated to around 94-98°C. - This high temperature causes the hydrogen bonds between the DNA strands to break, resulting in two single strands. #### 2. Annealing: - The temperature is lowered to around 50-65°C. - Short DNA sequences called primers bind (or anneal) to the complementary sequences on the single-stranded DNA templates. #### 3. Extension: - The temperature is raised to around 72°C. - Taq polymerase (a heat-stable enzyme) attaches to the primers and starts adding nucleotides to the 3’ end of each primer, synthesizing new DNA strands complementary to the original template strands. ### PCR Cycle Illustration: Each PCR cycle involves three steps: Denaturation, Annealing, and Extension. These steps are repeated multiple times (typically 25-35 cycles), leading to exponential amplification of the target DNA sequence. Here is the detailed process for three cycles: #### **Cycle 1:** - **Denaturation:** The DNA is heated to 94-98°C, separating it into single strands. - **Annealing:** The temperature is lowered to 50-65°C, allowing primers to bind to the single-stranded DNA. - **Extension:** The temperature is raised to 72°C, and Taq polymerase synthesizes new strands, resulting in two double-stranded DNA molecules from the original one. #### **Cycle 2:** - **Denaturation:** The two double-stranded DNA molecules are heated again to separate into single strands. - **Annealing:** Primers bind to the new single-stranded templates. - **Extension:** Taq polymerase synthesizes new DNA, resulting in four double-stranded DNA molecules. #### **Cycle 3:** - **Denaturation:** The four double-stranded DNA molecules are heated to separate into single strands. - **Annealing:** Primers bind to these new single-stranded templates. - **Extension:** Taq polymerase
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