Extension

Definition

In the context of the Polymerase Chain Reaction (PCR), extension refers to the process of DNA synthesis where the DNA polymerase enzyme adds complementary nucleotides to the growing DNA strand, elongating the newly synthesized DNA molecule.

5 Must Know Facts For Your Next Test

1. The extension step in PCR is carried out at a specific temperature, typically around 72°C, which is the optimal temperature for the DNA polymerase enzyme to function efficiently.
2. During the extension step, the DNA polymerase enzyme reads the template strand and adds complementary nucleotides to the growing DNA strand, resulting in the synthesis of a new double-stranded DNA molecule.
3. The length of the extension step is determined by the length of the target DNA sequence, with longer sequences requiring a longer extension time to ensure complete synthesis.
4. The number of extension cycles in a PCR protocol is crucial, as it determines the final yield of the target DNA sequence, with more cycles leading to a higher amplification.
5. The efficiency of the extension step can be affected by various factors, such as the concentration and activity of the DNA polymerase enzyme, the presence of inhibitors, and the quality of the DNA template.

Review Questions

• Explain the role of the extension step in the Polymerase Chain Reaction (PCR) process.
  • The extension step in PCR is a crucial part of the DNA amplification process. During this step, the DNA polymerase enzyme reads the template strand and adds complementary nucleotides to the growing DNA strand, resulting in the synthesis of a new double-stranded DNA molecule. The length of the extension step is determined by the length of the target DNA sequence, and the number of extension cycles is crucial in determining the final yield of the target DNA sequence.
• Describe how the efficiency of the extension step can be affected in the Polymerase Chain Reaction (PCR) process.
  • The efficiency of the extension step in PCR can be affected by various factors, such as the concentration and activity of the DNA polymerase enzyme, the presence of inhibitors, and the quality of the DNA template. For example, a low concentration of the DNA polymerase enzyme or the presence of inhibitors can reduce the efficiency of the extension step, leading to a lower yield of the target DNA sequence. Additionally, the quality of the DNA template, such as the presence of contaminants or degradation, can also impact the efficiency of the extension step.
• Analyze the relationship between the extension step and the overall amplification of the target DNA sequence in the Polymerase Chain Reaction (PCR) process.
  • The extension step is directly linked to the overall amplification of the target DNA sequence in the PCR process. The number of extension cycles is a critical factor in determining the final yield of the target DNA sequence. More extension cycles lead to a higher amplification, as each cycle results in the synthesis of new double-stranded DNA molecules. However, the efficiency of the extension step can also affect the amplification, as factors such as the concentration and activity of the DNA polymerase enzyme, the presence of inhibitors, and the quality of the DNA template can influence the rate and accuracy of the DNA synthesis. Therefore, optimizing the extension step is crucial for achieving efficient and accurate amplification of the target DNA sequence in the PCR process.

Related terms

Denaturation:

The process of separating the double-stranded DNA molecule into single strands by applying heat, which disrupts the hydrogen bonds between the base pairs.

Annealing:

The step where short DNA sequences called primers bind to their complementary sequences on the single-stranded DNA template, providing a starting point for DNA synthesis.

Amplification:

The exponential increase in the number of copies of a specific DNA sequence during the PCR process.