DNA Replication Lecture Notes

Introduction

• DNA: Codes for traits, vital for cell function.
• DNA Replication: Process of making more DNA, essential before cell division.

Where and When DNA Replication Occurs

• Location:
  • Eukaryotic cells: Occurs in the nucleus.
  • Prokaryotic cells: Occurs despite the absence of a nucleus.
• Timing:
  • Occurs during interphase, before mitosis or meiosis.

Key Players in DNA Replication

• Enzymes: Crucial for speeding up reactions.
  • Helicase: Unzips DNA strands by breaking hydrogen bonds.
  • DNA Polymerase: Synthesizes new DNA strands.
  • Primase: Creates RNA primers for DNA polymerase.
  • Ligase: Glues DNA fragments together.

DNA Replication Process

• Initiation:

  • Starts at the origin, identified by specific DNA sequences.
  • Helicase unwinds DNA at the origin.
  • SSB Proteins prevent strands from reannealing.
  • Topoisomerase prevents supercoiling during unwinding.

• Primer and Synthesis:

  • Primase adds RNA primers for initiation.
  • DNA Polymerase builds new strands (5’ to 3’ direction).

DNA Strand Details

• Antiparallel Nature:

  • DNA strands run in opposite directions (5’ to 3’ and 3’ to 5’).
  • Important for replication directionality.

• Leading vs. Lagging Strand:

  • Leading Strand: Continuous replication.
  • Lagging Strand: Discontinuous replication with Okazaki fragments.
  • Okazaki Fragments: Short DNA segments on the lagging strand.
  • Ligase: Seals Okazaki fragments into a continuous strand.

Result of Replication

• Semi-Conservative Replication:
  • Each new DNA molecule contains one original and one new strand.

Error Checking and Implications

• Proofreading by DNA Polymerase:

  • Corrects mismatched bases, preventing errors in gene coding.

• Medical Applications:

  • Understanding replication aids in developing treatments against harmful cells (e.g., cancer, bacteria).

Conclusion

• DNA replication is a complex, highly regulated process.
• Encouragement to explore further details and applications.

Stay curious and explore more about DNA replication!