WK8.18 Polymerase Chain Reaction PCR (Slides)

Learning Outcomes

  • LO1: Describe the steps involved in PCR.
  • LO2: List several applications of PCR.

Overview of PCR

  • Polymerase Chain Reaction (PCR): A technique used to amplify specific DNA sequences through repeated cycles.
  • Key Components of PCR:
    • DNA Template: A single-stranded DNA that serves as a template for synthesis.
    • Primers: Short segments of DNA that bind to the template and specify the region of DNA to be amplified.
    • DNA Polymerase: Enzyme that synthesizes new DNA strands.
    • Deoxynucleotide Triphosphates (dNTPs): Building blocks of DNA used in the synthesis of new DNA strands.

Key Steps in PCR

  1. Denaturation:

    • The double-stranded DNA template is heated (typically to around 100°C) to separate the strands.

  2. Annealing:

    • The temperature is lowered (around 60-70°C) to allow primers to bind (anneal) to the template DNA.

  3. Extension:

    • The temperature is adjusted (around 70°C) to enable DNA polymerase to synthesize the new DNA strand by adding dNTPs to the growing chain.

  4. Cycles:

    • The process typically consists of 30-40 cycles, leading to exponential amplification of the target DNA.
    • Each cycle doubles the amount of target DNA.

Applications of PCR

  • Medical Diagnostics: Detection of diseases, including viral infections like COVID-19.
  • Forensic Science: Used for DNA fingerprinting and paternity testing, matching DNA from crime scenes.
  • Genetic Research: Amplifying genes for cloning, sequencing, and mutation analysis.

Visualizing PCR Products

  • Gel Electrophoresis: Used to separate and visualize amplified DNA fragments.
    • Principle: DNA fragments are separated in a gel matrix based on size when an electric current is applied.
    • Staining: DNA can be stained with fluorescent dyes to visualize bands under UV light.

Genetic Variability and PCR

  • Simple Sequence Repeats (SSRs):
    • Repeated sequences in the genome that vary among individuals.
    • These variations are useful in genetic fingerprinting.
  • PCR to Amplify SSRs: Design primers that bind to sequence regions adjacent to the SSR to study genetic differences.

History and Impact of PCR

  • Developed by Kary Mullis: Introduced in the 1980s, PCR has revolutionized molecular biology and genetics.
    • Taq Polymerase: Enzyme from Thermus aquaticus that is stable at high temperatures, essential for PCR.

Conclusion

  • PCR is a powerful tool for amplifying specific DNA sequences, leading to numerous applications in research, healthcare, and forensic investigations.
  • It allows for the simple detection and analysis of DNA, impacting various fields such as genetics, medicine, and law enforcement.