Lecture on DNA Replication

Introduction to DNA

• DNA is the ultimate director for cells, coding for traits.
• Important for cell division to ensure new cells receive DNA.

DNA Replication

• Definition: Process of making more DNA.
• Where:
  • Eukaryotic cells: Occurs in the nucleus.
  • Prokaryotic cells: Occurs without a nucleus.
• When:
  • Before cell division (mitosis or meiosis) during interphase in eukaryotic cells.

Key Enzymes in DNA Replication

• Helicase:
  • Unzips the two strands of DNA by breaking hydrogen bonds.
• DNA Polymerase:
  • Builds a new strand by replicating DNA molecules.
  • Has proofreading ability to ensure accuracy.
• Primase:
  • Creates an RNA primer so DNA polymerase knows where to start.
• Ligase:
  • Glues DNA fragments together.

Steps of DNA Replication

• Origin of Replication:
  • Specific DNA sequences identify the starting point.
• Unwinding:
  • Helicase unwinds DNA, SSB proteins keep strands apart, Topoisomerase prevents supercoiling.
• Primer Placement and Synthesis:
  • Primase places RNA primers on both strands.
• Strand Synthesis:
  • DNA polymerase builds new strand in 5’ to 3’ direction.
  • Leading strand: Continuous synthesis.
  • Lagging strand: Discontinuous synthesis with Okazaki fragments.

Directionality of DNA

• DNA strands are anti-parallel (5' to 3' vs 3' to 5').
• DNA Polymerase adds new bases to the 3’ end.

Finalization of DNA Replication

• Okazaki Fragments:
  • Formed on the lagging strand and glued by ligase.
• Semi-conservative Replication:
  • Each new DNA molecule has one original and one new strand.

Error Correction

• DNA polymerase's proofreading ability minimizes errors.
• Errors can lead to incorrect proteins if not corrected.

Importance of DNA Replication Understanding

• Applications:
  • Medical treatments that target DNA replication in harmful cells.

Conclusion

• Further exploration is encouraged.
• Staying curious is important.

"End of lecture: Remember to explore beyond the basics and stay curious."