Lecture Notes: DNA Replication

Introduction to DNA Replication

• DNA is the director for cellular functions and codes traits.
• Replication is crucial for cell division, ensuring daughter cells receive a DNA copy.

Where and When DNA Replication Occurs

• Where:
  • Eukaryotic cells: Occurs in the nucleus.
  • Prokaryotic cells: Lack a nucleus but still undergo replication.
• When:
  • Occurs before cell division (mitosis or meiosis) during interphase.

Key Players in DNA Replication

• Enzymes: Speed up reactions, build up or break down substances they act upon.
• Helicase: Unzips DNA strands by breaking hydrogen bonds.
• DNA Polymerase: Builds new DNA strands by replicating DNA molecules.
• Primase: Initializes replication by creating RNA primers for DNA polymerase.
• Ligase: Glues DNA fragments together.

The Process of DNA Replication

• Origin: Replication starts at specific DNA sequences known as the origin.
• Unwinding:
  • Helicase unwinds DNA, while SSB proteins prevent re-attachment of strands.
  • Topoisomerase prevents DNA supercoiling.
• Primer Placement: Primase lays down RNA primers.
• Strand Directionality:
  • DNA strands are anti-parallel (5' to 3' and 3' to 5').
  • DNA polymerase adds new bases to the 3' end, building in the 5' to 3' direction.

Leading and Lagging Strands

• Leading Strand: Built continuously in the 5' to 3' direction.
• Lagging Strand:
  • Built in segments called Okazaki fragments due to directional constraints.
  • Primers are frequently placed; ligase seals gaps between fragments.

Result of Replication

• Semi-Conservative Replication:
  • Each new DNA molecule consists of one original and one new strand.
• Proofreading by DNA Polymerase:
  • Minimizes errors to ensure correct gene coding.

Importance of Understanding DNA Replication

• Essential for developing treatments that target replication in harmful cells.

Conclusion

• DNA replication is a detailed process with much more to explore beyond the basics.
• Encouragement to stay curious and explore further into the topic.