DNA Replication Lecture Notes

Introduction to DNA

• DNA is the ultimate director for cells.
• Codes for traits and is crucial during cell division.

Topic Overview: DNA Replication

• Definition: The process of making more DNA.
• Where:
  • In eukaryotic cells, occurs in the nucleus.
  • Prokaryotic cells lack a nucleus but also replicate DNA.
• When:
  • Occurs before cell division (mitosis or meiosis) during interphase.

Key Players in DNA Replication

• Enzymes involved:
  • Helicase: Unzips the DNA strands by breaking hydrogen bonds.
  • DNA Polymerase: Builds new DNA strands by replicating DNA molecules.
  • Primase: Initializes replication by creating a primer (made of RNA) for DNA polymerase.
  • Ligase: Glues together DNA fragments.

Important Concepts

• Origin of Replication: Specific DNA sequences signal where replication begins.
• SSB Proteins: Single stranded binding proteins that keep the DNA strands apart.
• Topoisomerase: Prevents supercoiling of DNA during replication.

DNA Structure Basics

• DNA consists of two complementary strands that are anti-parallel.
• Directionality:
  • 5’ to 3’ and 3’ to 5’ strands.
  • Carbons in the sugar backbone of DNA are numbered for orientation.

Process of DNA Replication

• Leading Strand:
  • Synthesized continuously in the 5’ to 3’ direction.
• Lagging Strand:
  • Synthesized discontinuously, requiring multiple primers, leading to Okazaki fragments.
• Replacement of Primers: RNA primers are replaced with DNA bases.
• Sealing Fragments: Ligase seals the gaps between Okazaki fragments.

Result of DNA Replication

• Ends with two identical double helix DNA molecules.
• Described as semi-conservative: each new molecule has one original and one new strand.

Error Checking

• DNA polymerase has proofreading ability to minimize errors in base pairing.
• Importance of accuracy: Incorrect base pairing affects gene coding and protein production.

Conclusion

• Understanding of DNA replication leads to medical advancements, such as treatments for harmful cells.
• Further exploration is encouraged to gain detailed insights.
• Reminder to stay curious.