Lecture Notes: DNA Replication

Introduction

• DNA is crucial for cells, coding for traits.
• DNA replication is necessary during cell division to ensure daughter cells receive DNA.

Where and When of DNA Replication

• Eukaryotic Cells: Replication occurs in the nucleus during interphase before mitosis or meiosis.
• Prokaryotic Cells: Lack a nucleus but still undergo DNA replication, although the process differs.

Key Enzymes in DNA Replication

• Enzymes: End in "-ase" and catalyze reactions.
• Helicase: Unzips DNA strands by breaking hydrogen bonds.
• DNA Polymerase: Builds new DNA strands by replicating DNA molecules.
• Primase: Creates RNA primers to guide DNA polymerase.
• Ligase: Glues DNA fragments together.

DNA Replication Process Overview

• Origin of Replication: Starts with certain DNA sequences.
• Helicase: Unwinds DNA.
• SSB Proteins: Prevent re-attachment of DNA strands.
• Topoisomerase: Prevents DNA supercoiling.
• Primase: Lays RNA primers for DNA polymerase.
• DNA Polymerase:
  • Adds bases in the 5' to 3' direction.
  • Leading Strand: Continuous synthesis.
  • Lagging Strand: Discontinuous synthesis forming Okazaki fragments.
  • RNA primers replaced with DNA bases; ligase seals gaps.
• Result: Two identical DNA molecules (semi-conservative replication).

DNA Strands and Directionality

• DNA strands are anti-parallel: 5' to 3' and 3' to 5'.
• Sugar in DNA backbone has carbons numbered 1' to 5'.

Proofreading and Error Correction

• DNA Polymerase has proofreading abilities to minimize errors.
• Errors could lead to incorrect protein formation.

Importance and Applications

• Detailed understanding aids in medical treatments, targeting DNA replication in harmful cells.

Conclusion

• Encouragement to explore beyond basics and stay curious.