DNA Replication

Introduction

• DNA is the ultimate director for cells, coding for traits.
• Key in cell division to ensure new cells receive a DNA copy.

Where and When DNA Replication Occurs

• Where:
  • In eukaryotic cells, occurs in the nucleus.
  • Prokaryotic cells perform DNA replication without a nucleus.
• When:
  • Occurs before cell division.
  • Specifically during interphase before mitosis or meiosis.

Key Players in DNA Replication

• Enzymes
  • Helicase: Unzips the DNA strands by breaking hydrogen bonds.
  • DNA Polymerase: Builds new DNA strands by replicating DNA molecules.
  • Primase: Makes RNA primers for DNA polymerase to start replication.
  • Ligase: Glues DNA fragments together, important for the lagging strand.

The Process of DNA Replication

• Starts at the "origin," identified by specific DNA sequences.
• Steps Involved:
  1. Helicase: Unwinds the DNA.
  2. SSB Proteins: Bind to keep strands separated.
  3. Topoisomerase: Prevents supercoiling during unwinding.
  4. Primase: Creates RNA primers on both strands.
  5. DNA Polymerase: Builds new DNA strands.
     • Works in a 5’ to 3’ direction.

DNA Structure

• DNA strands are complementary and anti-parallel.
• Directionality:
  • 5’ to 3’ or 3’ to 5’ based on carbon numbering in the sugar.

Leading vs. Lagging Strand

• Leading Strand:
  • Built continuously in 5’ to 3’ direction by DNA polymerase.
• Lagging Strand:
  • Built discontinuously in Okazaki fragments, requiring multiple primers.
  • Ligase: Seals gaps between Okazaki fragments.

Proofreading and Errors

• DNA Polymerase has proofreading abilities to minimize errors.
• Ensures correct gene coding and protein synthesis.

Importance and Applications

• Semi-conservative nature of DNA replication.
• Key understanding has led to medical treatments targeting harmful cells.
• Encouragement to explore further reading for more details.

Conclusion

• DNA replication is crucial for cell division and genetic fidelity.
• Further study can uncover more detailed processes and applications.
• Stay curious and continue exploring!