DNA Replication Lecture Notes

Introduction to DNA

• DNA is the ultimate director for cells, coding for traits.
• DNA replication is essential during cell division to ensure daughter cells receive DNA.

Key Concepts of DNA Replication

Where and When

• Location of Replication:
  • Eukaryotic cells: occurs in the nucleus.
  • Prokaryotic cells: do not have a nucleus, but they also replicate DNA.
• Timing of Replication:
  • Occurs before cell division (mitosis or meiosis) during interphase.

Key Players in DNA Replication

Enzymes and Their Functions

• Helicase:
  • Unzipping enzyme that breaks hydrogen bonds between DNA bases.
• DNA Polymerase:
  • Builder enzyme that replicates DNA to build a new strand.
• Primase:
  • Initializes the replication by creating RNA primers for DNA polymerase to start working.
• Ligase:
  • Glues together DNA fragments.

Additional Proteins

• Single-Stranded Binding (SSB) Proteins:
  • Bind to separated DNA strands to keep them apart.
• Topoisomerase:
  • Prevents supercoiling of DNA during replication.

DNA Structure and Directionality

• DNA has two complementary strands that run antiparallel (5' to 3' and 3' to 5').
• Understanding the carbon numbering in the DNA sugar backbone is crucial (1' to 5').

Process of DNA Replication

1. Origin of Replication:
   • Identified by specific DNA sequences.
2. Unwinding DNA:
   • Helicase unwinds the DNA.
3. Primer Placement:
   • Primase places RNA primers on both strands.
4. Building New Strands:
   • DNA polymerase builds new strands in the 5' to 3' direction.
   • Leading Strand: Continuous replication toward the unwinding.
   • Lagging Strand: Discontinuous replication due to directionality, forming Okazaki fragments.
5. Sealing Gaps:
   • Ligase seals gaps between Okazaki fragments after replacing RNA primers with DNA bases.

Final Outcomes of Replication

• Results in two identical double helix DNA molecules.
• Process is semi-conservative; each new DNA contains one original strand and one new strand.

Proofreading and Error Correction

• DNA polymerase has proofreading ability to minimize errors in base pairing, preventing incorrect genes or proteins.

Applications of DNA Replication Knowledge

• Understanding DNA replication has led to medical treatments targeting harmful cells (e.g., cancer, bacterial infections).

Conclusion

• Further exploration of DNA replication mechanisms is encouraged for deeper understanding.
• Stay curious and continue learning!