DNA Replication Lecture Notes

Introduction to DNA

• DNA is the ultimate director for cells and codes for traits.
• Important for cell division to ensure new daughter cells receive DNA.

Overview of DNA Replication

• Definition: The process of making more DNA.
• Location:
  • Eukaryotic Cells: Occurs in the nucleus.
  • Prokaryotic Cells: Lack a nucleus but still undergo DNA replication.
• Timing: Happens before cell division (mitosis or meiosis) during interphase.

Key Players in DNA Replication

• Enzymes: Most key players are enzymes, which speed up reactions.
  • Helicase: Unzips the DNA by breaking hydrogen bonds between bases.
  • DNA Polymerase: Builder enzyme that replicates DNA molecules.
  • Primase: Initializes replication by creating RNA primers for DNA polymerase to start.
  • Ligase: Glues DNA fragments together.

DNA Replication Process

1. Origin of Replication: Identified by specific DNA sequences.
2. Unwinding DNA:
   • Helicase unwinds the DNA strands.
   • SSB Proteins: Bind to DNA strands to keep them separated.
   • Topoisomerase: Prevents supercoiling of DNA during unwinding.
3. Primer Synthesis:
   • Primase synthesizes RNA primers needed for DNA polymerase.
4. DNA Building Direction:
   • DNA strands are anti-parallel (5' to 3' and 3' to 5').
   • DNA polymerase can only build in the 5' to 3' direction.
   • Leading Strand: Continuous synthesis in the 5' to 3' direction.
   • Lagging Strand: Discontinuous synthesis, forms Okazaki fragments due to multiple priming.
5. Sealing Fragments:
   • Ligase seals gaps between Okazaki fragments after RNA primers are replaced with DNA bases.

Final Result of Replication

• Two identical double helix DNA molecules produced from one original molecule.
• Semi-Conservative: Each new DNA molecule contains one old and one new strand.

Importance of Accuracy

• DNA polymerase has proofreading ability to prevent errors in base pairing, ensuring correct gene coding.

Applications of Understanding DNA Replication

• Insights into DNA replication have led to medical treatments targeting harmful cells.

Conclusion

• Explore further beyond the basics for a deeper understanding.
• Stay curious!