Higher Biology - DNA Replication and PCR

Introduction

• Focus on DNA replication and the Polymerase Chain Reaction (PCR).
• Previous topics included DNA structure, bonds, and 3’ and 5’ ends.

DNA Replication

• Purpose: DNA replication ensures that each daughter cell receives an exact copy of the DNA during cell division.
• Stages:
  1. Original DNA Strand: Splitting occurs at weak hydrogen bonds between complementary base pairs.
  2. Replication Fork: DNA unwinds, and strands unzip to form two template strands.
  3. Leading vs. Lagging Strand:
     • Leading Strand: 3’ end, continuous replication.
     • Lagging Strand: 5’ end, replication occurs in fragments.

Key Components

• Primers: Short sequences of nucleotides required to start new DNA strands.
• DNA Polymerase: Enzyme adding complementary nucleotides to form new DNA strands.
• Ligase: Enzyme joining fragments of DNA on the lagging strand.
• ATP: Required energy source for DNA replication.

Polymerase Chain Reaction (PCR)

• Purpose: Amplify DNA in a lab setting for various tests and applications.
• Process:
  1. Denaturation: Heat DNA to 92-98°C to break hydrogen bonds.
  2. Annealing: Cool to 50-65°C to allow primers to bind.
  3. Extension: Heat to 70-80°C for DNA polymerase to synthesize new strands.
• Outcome: Each cycle doubles the DNA, leading to exponential amplification.

Applications

• Forensics: Amplify small DNA samples from crime scenes.
• Paternity Testing: Determine familial relationships.
• Medical Diagnostics: Detect genetic disorders from embryonic DNA.

Requirements for PCR

• Original DNA strand.
• Primers and nucleotides.
• pH buffer to maintain optimal conditions.
• Heat-tolerant DNA polymerase.
• Thermal cycler for temperature cycling.

Conclusion

• DNA replication and PCR are essential for cell division and laboratory DNA analysis.
• The process of DNA replication and PCR involves specific enzymes and conditions to ensure accuracy and efficiency.