DNA Replication Lecture Notes

Introduction

• DNA structure and function overview.
• Focus on DNA processes, starting with replication.

DNA Replication Overview

• Purpose: Duplicate DNA for cell division.
• Timing: Occurs during S phase (synthesis phase) of interphase.
• Process:
  • Separate strands of the double helix.
  • Add new nucleotides to create two new molecules.
  • Result: Two identical daughter molecules.

Visualizing the Process

• Imagine the processes as they happen.
• Use videos for better conceptualization.

Key Terms and Concepts

• Origin of Replication: Starting point of replication.
• Replication Bubble: Area where DNA starts to unwind.
• Replication Fork: V-shaped region where strands separate.

Enzymes Involved in DNA Replication

Topoisomerase

• Unwinds the DNA helix.

Helicase

• Separates DNA strands by breaking hydrogen bonds.

Single-Strand Binding Proteins (SSBPs)

• Prevent re-annealing of strands.

Polymerases

• General Function: Add nucleotides to new strands.
• Types:
  • DNA Polymerase III: Main enzyme for adding new DNA nucleotides.
  • Primase: Lays down RNA primer to start DNA synthesis.
  • DNA Polymerase I: Replaces RNA primers with DNA nucleotides.

Directionality and Strand Synthesis

• DNA strands are anti-parallel.
• Leading Strand: Synthesized continuously in the same direction as replication fork.
• Lagging Strand: Synthesized in Okazaki fragments, opposite direction of fork.
• Okazaki Fragments: Short DNA segments on the lagging strand.

DNA Ligase

• Function: Joins Okazaki fragments and seals gaps in the DNA backbone.

Semi-Conservative Replication

• Each daughter DNA molecule has one old and one new strand.

Mutation and Proofreading

• Mutation: Rare errors in DNA replication.
• Proofreading: DNA polymerases can correct errors.
• Significance of Mutations:
  • Not all are harmful.
  • Can be neutral or advantageous.
  • Drive evolution via beneficial phenotypic changes.

Study Tips

• Ensure understanding of enzyme functions and strand directionality.
• Use diagrams and videos to reinforce understanding.
• Review the anti-parallel nature of DNA strands for clarity.

Conclusion

• DNA replication is a fundamental process with intricate mechanisms.
• Understanding these processes is crucial for further study in genetics.