DNA Replication Lecture Notes

Introduction to DNA and its Importance

• DNA is the ultimate director for cells and codes for traits.
• Essential to replicate DNA during cell division to ensure new daughter cells receive a copy.

Where and When DNA Replication Occurs

• Eukaryotic Cells: DNA replication occurs in the nucleus.
• Prokaryotic Cells: Also perform DNA replication, though they lack a nucleus.
• Occurs before cell division during interphase, prior to mitosis or meiosis.

Key Players in DNA Replication

• Helicase: Unzips the DNA strands by breaking hydrogen bonds.
• DNA Polymerase: Builds new DNA strands by replicating DNA molecules.
• Primase: Creates RNA primers to indicate where DNA polymerase should start.
• Ligase: Glues DNA fragments together.

The Process of DNA Replication

1. Origin Identification: Begins at specific DNA sequences called origins.
2. Unwinding DNA:
   • Helicase unwinds DNA at the origin.
   • Single Stranded Binding (SSB) proteins keep strands separated.
   • Topoisomerase prevents supercoiling which needs to be controlled.
3. Primer Placement:
   • Primase adds RNA primers to both strands to guide DNA polymerase.
4. Building New Strands:
   • Leading Strand: Built continuously in the 5’ to 3’ direction.
   • Lagging Strand: Built in segments (Okazaki fragments) due to anti-parallel nature.
5. Completion:
   • RNA primers replaced with DNA bases.
   • Ligase seals Okazaki fragments.
   • Resulting in two identical double helix DNA molecules.

Important Concepts

• Semi-conservative Replication: Each new DNA contains one original and one new strand.
• Proofreading Ability of DNA Polymerase: Ensures high accuracy by correcting mismatched DNA bases, preventing errors in genes and proteins.

Applications and Further Exploration

• Detailed understanding aids in developing treatments against pathogenic bacteria and cancer cells.
• Encouragement to explore further materials for deeper understanding.

• Conclusion: DNA replication is a complex but well-ordered process essential for genetic continuity. Stay curious and keep exploring!

• Reminder: Further reading materials are suggested for expanded learning. Stay curious!