DNA Replication Lecture Notes

Introduction

• DNA: Codes for traits and directs cell functions.
• Importance: Necessary for cell division to ensure daughter cells receive DNA.

Where & When DNA Replication Occurs

• Where:
  • Eukaryotic cells: In the nucleus.
  • Prokaryotic cells: No nucleus; different replication process.
• When:
  • Before cell division (mitosis or meiosis) during interphase.

Key Players in DNA Replication

• Enzymes: Speed up reactions; often end in "-ase."
  • Helicase: Unzipping enzyme that breaks hydrogen bonds between DNA strands.
  • DNA Polymerase: Builds new DNA strand by replicating DNA molecules.
  • Primase: Initializes the process by creating RNA primers.
  • Ligase: Glues DNA fragments together.

DNA Replication Process

1. Origin: Specific DNA sequence where replication starts.
2. Helicase: Unwinds the DNA strands.
3. SSB Proteins: Bind to keep strands separate.
4. Topoisomerase: Prevents DNA supercoiling.
5. Primase: Creates RNA primers for initiation.
6. DNA Polymerase: Builds new DNA strands.
   • Directionality: DNA strands are anti-parallel (5' to 3' and 3' to 5').
   • Leading Strand: Built continuously in the 5' to 3' direction.
   • Lagging Strand: Built in fragments (Okazaki fragments) due to directionality.
   • Primers replaced with DNA bases.
7. Ligase: Seals gaps between Okazaki fragments.

Result of Replication

• Produces two identical double helix DNA molecules.
• Semi-conservative: Each copy has one old strand and one new strand.

Error Checking

• DNA Polymerase: Proofreads to minimize errors.
• Errors can lead to incorrect gene coding and protein synthesis issues.

Further Exploration

• Detailed understanding aids in medical treatments, including cancer therapies.
• Encouragement to explore beyond basic understanding.

Closing

• Maintain curiosity for further learning opportunities.